Medical Zoology PDF Past Paper - Premed Semester 1

Medical Zoology Premed – Semester 1 The Protista Eukaryotic Evolution 3.5 billion years ago there was very little oxygen in the atmosphere As prokaryotes developed, they started metabolising and increasing atmospheric oxygen concentrations....

Medical Zoology Premed – Semester 1 The Protista Eukaryotic Evolution 3.5 billion years ago there was very little oxygen in the atmosphere As prokaryotes developed, they started metabolising and increasing atmospheric oxygen concentrations. This allowed single celled eukaryotes to develop The ancestor of modern-day eukaryotic cells engulfed a heterotrophic aerobic prokaryote by phagocytosis o This made the cell more efficient o It was passed down through the generations and has become the mitochondrion o It allowed eukaryotic cells to use oxygen Taxonomy Living things are divided into three domains, bacteria, archea and eukarya. Kingdom Protista is no longer recognised o The word protist refers to eukarya that are neither plants, animals or fungi Diplomonads Lack plastids and their mitochondria are highly reduced Lack DNA, the electron transport chain and enzymes of the citric acid cycle Most are found in anaerobic environments Structure o Two equal sized nuclei o Multiple flagella Example: Giardia o Common intestinal parasite o Causes diarrhea, dehydration and intestinal pain o Coats the intestinal wall, feeding on mucous secretions. This affects absorption of fatty acids o Infection occurs by ingesting cysts through contaminated food or water o Life cycle: Cyst, trophozoite (active feeding stage), replication, cyst (All in the body) o Trophozoites and cysts are passed in stool but only cysts are infective – the trophozoites do not survive in the environment Parabasalid Aoife Donohue 2018  Lack plastids and their mitochondria are highly reduced Lack DNA, the electron transport chain and enzymes of the citric acid cycle Most are found in anaerobic environments Structure o Undulating membrane used in locomotion o Multiple flagella o Have a parabasal fibre – a fibrous root of a flagella o Endosymbionts of animals Example: Trichomonas vaginalis o Inhabits the reproductive and urinary tract of men and women o Causes infection when acidity of the vagina is disturbed o Usually asymptomatic in males Kinetoplastids Structure o The flagella contain a spiral or crystalline rod of unknown function o Have a single, large mitochondrion with an organised mass of DNA called a kinetoplast o Can be free-living consumers in water or parasites of animals, plants and other protists Example: Trypanosoma o Parasites of vertebrate blood o Cause trypanosomiasis o In Africa, T.spp. is carried by tsetse flies and causes sleeping sickness o Sleeping sickness is spread when a tsetse fly injects the human after feeding on its blood. The parasite reproduces in the bloodstream. It is then ingested by the fly when it eats the blood and is passed on. o A vascular and lymphatic infection is followed by an invasion of the central nervous system that gives rise to ‘sleeping’ symptoms, followed by death o In South America, T.cruzi. is carried by reduviid bugs and causes Chaga’s disease o The reduviid bugs bite the soft skin around the mouth and eyes and defecates. The parasite in the faeces is rubbed into the eye or bite. It enters the system. Example: Species of Leishmania o Cause a variety of ailments collectively called leishmaniasis o Oriental sores are characterised by skin boils. Apicomplexans Aoife Donohue 2018  The phylum Apicomplexa is placed in the clade Alveolata – characterised by membrane-bound sacs just under the plasma membrane All apicomplexans are parasites of animals o An example is plasmodium which causes malaria Rhizopodia Also known as the amoebozoans Can be found in any moist or aquatic habitat Many species are ectocommensals (live on the surface), some are endosymbiotic Example: Entamoeba histolytica o Causes amoebic dysentery o Spread by faecal contamination of food and water and is most common where sanitation is poor o Amoebae invade the intestine but may spread to the liver, lungs and other tissues o Infection is caused by the ingestion of cysts in contaminated food or water. o Cysts develop into the pathogenic trophozoite forms in the body o Highly evolved – it has incorporated bacterial DNA to help it survive o Most of its genome is dedicated to producing surface coat proteins to avoid detection by the immune system Platyhelminthes Definition of an Animal Animals are multicellular, heterotrophic eukaryotes with tissues that develop from embryonic layers o The zygote divides multiple times to become a blastula (a small, hollow ball of cells) o The Blastocoel is the hollow space inside the blastula o An invagination in the blastula wall forms a second layer of cells inside the blastula. This is known as gastrulation. The blastula is now a gastrula o Animal phylogeny was based on morphological and developmental comparisons o Now, animal phylogeny is based mainly on molecular data Symmetry Aoife Donohue 2018  Animals can be radially symmetrical or bilaterally symmetrical o Radial symmetry is a body plan in which the organism can be divided into similar halves by passing a plane at any angle along a central axis o Bilateral symmetry is a basic body plan in which the left and right sides of the organism can be divided into approximate mirror images of each other along the midline Tissues The germ layers of tissue that form through gastrulation go on to form different tissues in the mature animal. o The ectoderm forms outer surface and sometimes CNS o The endoderm forms lining of digestive tube and organs derived from it, such as liver and lungs in vertebrates o The mesoderm forms the muscles and most other organs between the digestive tract and outer surface Diploblastic animals have tissues derived from the endoderm and ectoderm Triploblastic animals have tissues derived from the endoderm, ectoderm and mesoderm Body Cavities Coelomate animals have a body cavity or coelom that separates the digestive tract from the outer wall. It is derived from mesoderm Pseudocoelomate animals have a cavity formed from the blastocoel, called the pseudocoelom Acoelomate animals lack a cavity altogether Protostome and Deuterostome Development Protostomes are organisms in which the mouth develops from the blastopore o In the eight-cell stage, their cells are arranged in a spiral and are determinate o Their coelom develops from solid masses of mesoderm Deuterostomes are organisms in which the anus develops from the blastopore o In the eight-cell stage, their cells are radial and indeterminate o Their coelom develops from evaginations in the gut Phylum Platyhelminthes Parasitic or free-living unsegmented worms Triploblastic, acoelomate, bilaterally symmetrical, flattened dorsoventrally Complex, but have an incomplete gut with a single opening. Tapeworms have no gut system Have a central nervous system Class tremotoda are flukes and class cestoda are tapeworms Aoife Donohue 2018  Parasitic flukes and tapeworms have characteristic modifications o No cephalisation. Have a head piece with hooks and suckers to attach to the host o Lack a complex nervous and gastrovascular system as they live in a stable environment and receive digested food o Have a hard outer shell called a tegument to protect them from the host’s digestive juices Tapeworms (cestodes) have specially adapted to live in the human gut. o The tegument of tapeworms is folded to increase surface area for gaseous exchange and the uptake of nutrients o the ‘microtriches’ (little barbs) interdigitate with the microvilli of the intestinal wall to allow it to remain in the gut. Use secondary hosts which are infected with larvae to transport from host to host Fasciola Hepatica – The Liver Fluke Occurs worldwide. Affects humans in areas where sheep and cattle are raised. Can also be picked up eating raw watercress. Life cycle: o Eggs passed in faeces. Develop on contact with water. Infect water snails. o Free swimming adults encyst on plants to be consumed o In the body, they move from the duodenum into the liver. Schistosomiasis Caused by Schistosoma – a group of trematodes Prevalent in sub-Saharan Africa. Life cycle: o Very similar as liver flukes, except, the enter the body through the skin. o Migrate into portal blood in liver and mature into adults. Cheap drug, praziquantel, can cure it. Beef and Pork tapeworms – Taenia saginata and Taenia solium Life cycle: o Eggs passed in faeces o Cows and pigs become infected by eating contaminated plants. o Eggs hatch penetrate the muscle and develop into cysts. o Humans are infected by eating raw or undercooked meat. o Adults live in the small intestine Nematodes Aoife Donohue 2018 Phylum Nemotoda Triploblastic, pseudocoelomate, bilaterally symmetrical, unsegmented Have a round cross section, covered by layered cuticle which is shed during growth Have a complete gut Muscles all run longitudinally Free living in most aquatic habitats, soil, moist plant tissues, body fluids and tissues of animals Examples of Diseases caused by Nematodes Ascaris lumbricoides is the largest nematode found in humans o Adults live in lumen of small intestine. o Eggs are passed with faeces and are infective after several weeks. o The larvae hatch in the intestine and burrow through to the circulatory system and are carried to the lungs. o They reside in the lungs for 2 weeks then penetrate through to the bronchial passage and ascend to the throat where they are swallowed and develop to adults in the small intestine. Trichinellosis is caused by Trichinella spiralis. Causes swellings and fever. o Humans get infected by eating undercooked infected pork that has juveniles encysted in its muscle. o In the intestine they mature and reproduce. o Females embed themselves in the gut wall and release more juveniles. o These travel into the muscle tissue where they encyst. Enterobius vermicularis, or the human pinworm, causes worms in children. o Eggs are released in the faeces and ingested. o Hatch in the small intestines and lay eggs on the perianal skin. o The females move on the perianal skin causing itching and reinfection. Filariasis A group of diseases caused by filarial worms Elephantiasis (Bancroftian) o Transmitted by peri-domestic mosquitos o Caused by different parasites in sub-Saharan Africa and the far east o Live in the lymphatic system and cause debilitation and oedema (fluid build up) which causes extreme swelling of the lower limbs and genitals o Mosquito pick up the parasites during a blood meal. They grow in the mosquitos and then are transferred back to humans where they mature River Blindness (onchocerciasis) o Transmitted by black flies which live near flowing water o Juvenile parasites invade the eye and die, causing blindness Aoife Donohue 2018  o Onchocerea have a similar lifecycle to Wuchereria bancrofti which causes elephantiasis o The parasites do not cause the disease, it is the bacteria inside them. The bacteria elicit an inflammatory immune response which causes blindness Arthropoda Structure of Arthropoda Triploblastic, coelomate, bilaterally symmetrical Body divided into discrete segments, groups of segments specialised as tagmata (head, thorax etc) Hard, rigid exoskeleton (constructed from chitin), shed periodically (ecdysis) to allow growth Complete gut Insect nuisance and phobia Insects live in close proximity to humans o Some species are numerous and live in close proximity to humans eg. Ants and silverfish o Some species live in dirt and are a sign of bad hygiene eg. Cockroaches o Some species bite and sting eg. Bees and wasps Entomophobia is an unwarranted phobic reaction to harmless insects Arachnophobia is an unwarranted phobic reaction to harmless spiders Venoms Insects sting to inflict pain in defence of the nest Stinger is a modified ovipositor (organ for laying eggs) o Worker bees and wasps are sterile females o Honey-bee stingers are barbed and cannot be retracted and reused o Wasp and ant stings are unbarbed and can be reused The venoms are usually polypeptides (enzymes or horomones) o Wasp venom causes vasodilation and relaxation of smooth muscle o Non-formicine ants inject a complex mixture of alkaloids o Formicine ants spray formic acid onto a bite as they have no stinging apparatus Often sting en masse to deter large animals Blister and itch (urtica) inducing insects to not inject toxins through a sting o Eg. Hairy caterpillars who release toxins on contact when their hairs are broken Allergens Exposure to arthropod allergens (low molecular weight proteins) can cause excessive immunological reactions Aoife Donohue 2018  o Most common allergy is to the faeces of house dust mites o Venomous and urticating insects cause the greatest danger when sensitized (previously exposed and allergy-sensitive) individuals are bitten again Insects which Cause disease Pediculosis – ‘vagabond’s disease’ is caused by lice o The body louse, pubic louse or head louse o Pediculosis is an infestation of the hairy parts of the body or clothing with the eggs, larvae or adults of lice o The crawling stages of this insect feed on human blood, which can result in severe itching o Body lice travel to the skin to feed and return back to the clothing Scabies – caused by the scabies mite o Transmission of mites between humans is by physical contact. o Male and female scabies mites mate on the skin, and the female borrows into the skin and causes problems o Her excretory and secretory products result in an intense itching followed in many instances by a rash and secondary infections Insects as vectors for disease Massive area of scientific research. Can transmit protists, viruses and nematodes Transfer of disease from the vector to the host may be mechanical or biological Mechanical transfer can occur when a vector acquires a parasite and then lands on human food. o The causative agent is transferred, it does not increase in the vector o There are usually other possible methods of transferring the parasite eg. Bad hygiene Biological transfer occurs due to a specific association between insect vector, pathogen and host. Transfer never occurs without all three components o The disease agent replicates in the vector host, and there is a high degree of specificity between vector and disease agent o Controlling the disease involves attempts to reduce vector numbers, interrupting contact between vector and host, and attacking the pathogen whilst in the host Disease Cycles Some pathogens complete life cycle solely within the insect vector and host – human malaria is an example of a disease with a single cycle o Single cycle diseases are rare in humans because they require long-term coevolution and Homo sapiens is of relatively recent origin in evolutionary terms Aoife Donohue 2018  o A single cycle disease requires a human rather than any alternative vertebrate for completion of the disease-causing organism’s life cycle Many insect-borne diseases that affect humans include a (non-human) vertebrate host o The non-human cycle is primary, and the sporadic inclusion of humans, in a secondary cycle, is not essential to maintain the disease o Animal hosts act as disease reservoirs and the disease is transferred to humans when they come into contact with the hosts eg. In banana plantations. The Pathogens Can be bacteria, protists, nematodes or viruses (known as arboviruses) Replication in both vector and host is required Complicated life cycles have evolved, particularly among the protists and nematodes Presence of the parasite in the vector appears not to harm the host insect Transmission occurs only at the right developmental stage of the parasite, following replication Transfer of parasites from vector to host or vice versa occurs during a blood meal, or through deposition of infected faeces close to the wound site Feeding and transmission is aided by anticoagulant salivary gland products Arboviruses are viruses that multiply in an invertebrate and vertebrate host o They have the ability to replicate in arthopods Diseases spread by Arthropods Epidemic Typhus is spread by rickettsias prowazekii o Transferred by lice o The bacteria multiply in the host, come out in its faeces and kill it. o Humans become infected by scratching infective faeces into the skin Plague is caused by Y. pseudotuberculosis o Flea vectors live in peri-domestic rats o As the rats die, the bacteria is transferred to humans o Possibility of an outbreak depends on sanitation and the previous year’s climate Mosquitos Species of mosquito There are many species of mosquito (Diptera, Nematocera, Culicidae) They are slender flies with small heads and long mouth parts. They have long, narrow wings. There are two important subfamilies of mosquito o Anophelinea rest with their heads down and the body inclined at 45 degrees. These transport malaria o Culicinae rest with their bodies held horizontally. These transport yellow fever Aoife Donohue 2018 Mosquito Life Cycle Only females feed on blood for protein to help them develop their eggs They lay their eggs on the surface of the water o Culex eggs are laid in floating rafts o Anopheles eggs are laid singly on the water’s surface The larvae and pulpae breath air through a tube. Mosquitos lay their eggs on standing water. An easy way to reduce the number of mosquitos present, is to reduce the amount of standing water The Feeding Mechanism The Labium ends in two labels to protect it The stylet is made up of the cutting equipment During feeding the labrum, mandibles and maxillae drive through the skin of the host Flexible labium remains bowed outside host Saliva, which may contain anticoagulants, is injected through the hypopharynx Blood flows freely or is pumped up the food canal formed by the labrum and mandibles During feeding: o All six legs are on the victim’s skin. The labella touches the skin and the maxillary palps are raised o The labium is folded back and the skin is punctured o Half the length of the stylet is inserted into the body o After feeding, she straightens her front legs, leans back and moves the labium from side to side so that the stylet fall back into place Malaria The protist which causes malaria is plasmodium which is an apicomplexan The vectors are mosquitos of the genus anopheles The disease follows a characteristic course o The prepatent period is directly following the infective bite o Patent period shows the first signs of the disease is blood cells o The incubation period is 9 -21 days after infection (depending on the species) o Clinical symptoms – cycles of fever followed by severe sweating and a characteristically enlarged spleen. The four main species of malaria are falciparum, vivax, malariae and ovale. o Falciparum is the biggest malaria killer through cerebral malaria or renal failure. Fever recurrence is at 48-hour intervals. It is confined to very warm areas of the world Aoife Donohue 2018  o Vivax is less serious and rarely kills. The fever recurs every 48 hours. The disease may persist for up to 8 years with relapses several months apart. More widespread than falciparum o Malariae is widespread but rare, and death can result through chronic renal failure. Recurrence of fever is every 72 h, and it is very persistent, with relapses occurring 50 years after the initial infection o Ovale is rare with a very long incubation period and relapses at 3 month intervals. The life cycle of falciparum o Sporozoites are injected into the bloodstream o They move into the liver and develop to merozoites o Merozoites infect red blood cells and replicate o Gametocytes are produced in the red blood cells. o These are taken up by another mosquito and develop in its gut to form a zygote o This develops into a sporozoite filled cyst on the outside of the gut which releases sporozoites into the saliva Malaria Epidemiology Endemic malaria occurs at a relatively constant incidence over successive years Epidemic malaria occurs when the number of cases in an endemic area rises, or it occurs in a new area Stable malaria occurs when there is little seasonal or annual variation in disease incidence – transmitted by strongly anthropophilic (human-loving) Anopheles vectors in warmer areas of the world, usually transmitting P. falciparum Unstable malaria is associated with sporadic epidemics – transmitted by short-lived zoophilic (animal-loving) mosquito vectors that may occur in massive numbers, usually transmitting P. vivax Factors which affect disease transmission Vector distribution – there are only a handful of mosquito species worldwide that can transmit malaria Vector abundance – The temperature and availability of water must allow the vectors to develop Vector survival rate – The mosquitos have a very short life expectancy and there is a period between feeding on an infected host and the sporozoites becoming available for transmission in which the mosquito is not infective. If it dies during this period, malaria is not transmitted. Older mosquitos constitute the majority of the infective population The anthropophilic nature of the vector – as the mosquito must feed on humans twice for malaria to be transmitted, the likelihood of a mosquito to feed on humans is important for disease transmission. Feeding interval – some mosquitos feed on humans more frequently than others Aoife Donohue 2018  Vector competence – not all mosquitos who feed on humans will become vectors for malaria. There is a lot of variation, even within species. Controlling Malaria Used to rely on insecticides and drugs, but now the mosquitos are becoming immune to the insecticides and the malaria is becoming immune to the drugs. Mechanical control measures are still effective o Oiling water surfaces o Mosquito nets Arboviruses Arboviruses are zoonotic - maintained in complex life cycles involving a nonhuman primary vertebrate host and a primary arthropod vector, remaining undetected until humans come into contact with the virus o Humans and animals are dead-end hosts as we do not transmit the disease The virus family Flaviviridae causes diseases such as yellow fever and encephalitis Yellow Fever o Occurs in tropical areas of Africa and the Americas o Has a massive impact in urban epidemics o Originate from yellow fever-infected individuals moving from a rural to an urban environment Encephalitis (West Nile Virus) o Diseases which cause inflammation of the brain o West Nile virus is now endemic in the United States Human Evolutionary Biology Evolution Evolution is descent with modification o Results in organisms better adapted to their current environment o The change in genetic composition of a population from one generation to the next Requirements for natural selection to occur o Variation in trait o Variation in reproductive success o Relationship between trait and reproductive success o State of the trait is heritable Natural selection does not create new traits, but edits or selects for traits already present in the population. The local environment determines which traits will be selected for or selected against in any specific population Aoife Donohue 2018  An example of evolution is MRSA Staphylococcus aureus commonly found on people S. aureus became resistant to penicillin in 1945, two years after it was first widely used S. aureus became resistant to methicillin in 1961, two years after it was first widely used Methicillin inhibits a protein used in bacterial cell walls so MRSA bacteria use a different cell wall protein When exposed to methicillin MRSA strains are more likely to survive and reproduce than non-resistant S. aureus strains MRSA strains are now resistant to many antibiotics MRSA can evolve quickly because of its large population size, huge genetic variation, horizontal gene flow and short generation time Natural Selection There are three modes of selection: o Directional selection favours individuals at one end of the phenotypic range o Disruptive selection favours individuals at both extremes of the phenotypic range o Stabilizing selection favours intermediate variants and acts against extreme phenotypes Studying Biological Traits Proximate analysis studies the immediate causes of a trait ie. DNA transcription, genetics etc. Ultimate analysis studies the evolutionary forces over time that caused the trait to develop Morning Sickness as a Biological Trait Morning sickness causes nausea and vomiting during pregnancy Proximate causes – Women produce more saliva during the first trimester which can be bitter tasting and cause vomiting An increase in progesterone levels may relax the muscles of the GI tract and cause reflux An increase in sensitivity to odours stimulates normal nausea triggers An increase in bilirubin due to increased liver enzymes Thalidomide was used to cure morning sickness but caused children to be born with deformed limbs Ultimate causes – The maternal and embryo protection hypothesis There are secondary plant chemicals in the human diet. Aromas and strong flavours in Aoife Donohue 2018  chemicals to deter herbivory. Small doses are fine but large doses can be allergens, mutagens or abortifacients. The mother is immunosuppressed during pregnancy. She has increases susceptibility to bacteria, fungi, parasites and viruses in foods. Toxoplasma gondii is acquired from handling or eating undercooked meat. It rarely affects people unless they are immunosuppressed. In pregnancy, it is linked to neurological birth defects, spontaneous abortion and neonatal diseases To test the hypothesis, we can make predictions and test their truth. Prediction 1: Nausea and vomiting in pregnancy should peak when the embryo is most susceptible to disruption and the immune-vulnerability of the mother and embryo are at their greatest. This is shown to be true as morning sickness is worst on the first trimester when the baby is in embryogenesis and the mother is most vulnerable. Prediction 2: Foods that pregnant women find aversive should potentially contain plant toxins or pathogenic microorganisms, but foods that are craved should not. This is true. Women tend to have aversions to meat, vegetables, tea and coffee. They tend to crave foods that are very unlikely to contain secondary plant compounds. Prediction 3: Aversions to foods that potentially contain harmful substances should peak in the first trimester, when embryonic organogenesis is most sensitive to disruption. This is shown to be true Prediction 4: Nausea and vomiting of pregnancy should be associated with positive pregnancy outcomes. This is shown to be true as women who have miscarriages tend to be less likely to have NVP. Prediction 5: Expression of nausea and vomiting of pregnancy should depend on diet and should occur least often among women who are seldom exposed to foods that historically contained dangerous substances This is shown to be true as women who would have historically eaten plants, meat and rice are more likely to have NVP, whereas women who would have historically eaten corn do not. Conclusion: “Morning sickness” during pregnancy in women encountering potentially harmful foods may provide a selective advantage in terms of successful reproduction. Differential survival (natural selection) selects for women who experience “morning sickness” Aoife Donohue 2018  “Morning sickness” maintained as a human trait Some traits in humans display all characteristics necessary for selection Variation, differential reproduction, evolution Age at first reproduction depends in cultural, socio-economic and nutritional factors Natural selection can happen in three ways o Directional selection favours individuals at one end of the phenotypic range o Disruptive selection favours individuals at both extremes of the phenotypic range o Stabilizing selection favours intermediate variants and acts against extreme phenotypes What Selection Shapes Selection Maximises Reproduction Natural selection is the gradual natural process by which biological traits become either more or less common in population as a function of the effect of inherited traits on the differential reproductive success of organisms interacting with their environment o Selection maximises fitness – the ability to reproduce, not health or longevity o Human fitness is determined by survival to puberty and the end of reproductive life. o There is little selective pressure for health in middle or old age Example: the BRCA1/2 mutation o Predisposes women to breast and ovarian cancer o Not selected for because she has already passed it on to her offspring before she realises she has the mutation or not. o Carriers were more likely to have more children than non-carriers o After reproductive age, the carriers have lower survival rates than the general population Example: Sickle cell anaemia o Caused by a single base swap in the code for the beta strand of haemoglobin o Infected people tend to die young o Carriers were more likely to survive malaria because when the parasite entered the cell, it sickled quickly and allowed the body to remove it. o Offered advantage to the human population Symptoms – disease process or defence mechanism? Many disease symptoms considered a nuisance and medicated but may represent host evolved defences eg. Fever, coughing, diarrhoea etc. An example of this is fever. There are two possible interpretations of fever. Aoife Donohue 2018  o Fever may represent manipulation of the host by the pathogen. Perhaps viruses or bacteria release chemicals that cause the host to elevate its temperature to increase the pathogen’s reproductive rate o Fever may be an adaptive defence against the pathogen. Pathogen reproduction may be impeded, or immune response enhanced Case study: behavioural fever in the desert iguana o Desert iguanas are ectotherms and regulate their temperature by moving to warmer or cooler locations o When injected with dead bacteria they chose body temperatures 2o C higher than normal o Lizards were infected with live bacteria, then prevented from thermoregulating o Most lizards kept at temperatures mimicking behavioural fever survived o Most kept at lower temperatures died o In a study on its effects, all control lizards infected with bacteria developed behavioural fever and survived, but several given the medication (sodium salicylate) failed to develop fever and died o Behavioural fever in reptiles, amphibians, fishes, invertebrates broadly support the idea that fever is an adaptive response to infection In humans, it is not known definitively yet, it depends on the type of infection Neurosyphilis: o Julius Wagner-Jauregg noted that some syphilis patients improved after getting malaria and that syphilis was rare in areas where malaria was common o He intentionally infected thousands of syphilis patients with malaria o The fever from malaria caused them to go into remission from syphilis Chickenpox (varicella zoster virus) o Timothy Doran and colleagues studied 68 children with chickenpox o Experimental group took acetaminophen, control took placebo, double blind o Time to total scabbing 5.6 days versus 6.7 days (placebo:drug) o Itching less on day 4 when a placebo was taken Common cold (rhinovirus type 2) o Neil Graham and colleagues intentionally infected 56 adults, then treated some with over-the-counter medications o Placebo group suffered less stuffiness and made more antibodies o Studies show taking meds increases virus shedding phase o This could cause a 5% increase in annual influenza incidence Fever is very likely a very old adaptation o It is crazy to suggest it is always a bad idea to suppress fever o Fever may adaptive against some pathogens and not others o Fever carries costs even when beneficial o Very high fever is dangerous and fever after stroke is dangerous Aoife Donohue 2018 The Limits of Natural Selection What Makes us Human? There are many differences between ape and monkey characteristics. Apes: o Are usually larger and heavier than monkeys o Only live in Africa and Asia (monkeys also live in South America) o Have no tail o Are more upright body posture than monkeys – often able to walk on 2 legs o Have a broad chest o Rely on vision rather than smell (can distinguish colours) o Have shorter noses than some monkeys o Have a large brain to body size ratio compared with other animals o Can use tools/language and have complex social lives Primitive vs derived characteristics o Primitive characteristics are character traits that are inherited from the common ancestor of a group and has not changed much since. o Derived characteristics are unique to each species Primitive human characteristics o Fingernails/nail beds - Other mammals have claws o Clavicle/Shoulder Joint. This is an arboreal adaptation of apes and humans only o Hands/Thumbs - 5 digits, opposable thumbs o Dental Pattern - I 2/2, C 1/1, PM 2/2, M 3/3 o Large Brain which is associated with complex behaviour o Two Nipples/Single Offspring – Most mammals have litters o Vision – Front-facing eyes that facilitate 3-D vision, Trichromatic vision, dichromatic in other mammals o Short Snout – Reliance on smell reduced, switch to vision o Ears – large, basically round, highly cartilaginous structures emerging from the sides of their head o Extended Juvenile Period – Often lasting several years o Tool Use – Many primate species use tools, especially the apes o Culture and behaviours that are passed culturally o Vocal Communication/Deception – Many primates have elaborate vocalizations and can use deceptive calls o Resource defence deceptive alarm calls Unique (derived) human characteristics o Bipedality o Reduced Canines – This evolved in unison with bipedality. Chimps use their canines for aggression and display, our need for this was reduced Aoife Donohue 2018  o Extreme Tool Use/Hand Dexterity - More precise nervous control of individual fingers and grip o Culture Dominance – We organise into bigger groups than any other primate and have considerable variation in behaviours o Social Organization Beyond Close Kin – Chimps form groups of about 15-50 individuals o Paternal Parental Investment - Men invest more in child rearing than in other primates. o Extended Pair Bonds over mating - Attachment & exclusivity different from other primates o Abstract Symbol Interpretation/Body Decoration Human Characteristics and Constraints – Bipedalism Origins of Bipedality in Hominins o Chimpanzees and gorillas are our closest cousins o Earliest hominins presumed to be like living apes o Australopithecus seen as transitional between ape-like ancestor & early Homonids o Ardipithecus comes before Australopithecus o Living African apes not totally primitive, evolved in own direction o Ardipithecus group were already starting to be bipedal (not fully) Ardipithecus ramidus could walk upright o Limb proportions more like monkeys than apes - Feet functioned only partly like those of apes o Mobile lower back and probably had six lumbar vertebrae – there are three to four seen in the stiff backs of African apes o Unpredictably unique hand – Thumb musculature robust, unlike that of an ape, midcarpal joint allowed wrist to bend backward a great degree enhancing its ability to move along tree branches on its palm’s. Changes seen in apes to stiffen hands for suspension & vertical climbing not present o Locomotion did not resemble that of any living ape Ecological Evidence for Bipedality o Bipedality arose in woodland o The record of bipedalism is most graphically preserved in the fossilized footprints at Laetoli, Tanzania o 3.6-million-year-old tracks left by 2 individuals were uncovered in volcanic ash by Mary Leakey (1978-79) o Footprints were left by 2 australopithecines in damp volcanic ash Why did bipedalism become the primary adaptation of hominids? o Carrying behaviour Aoife Donohue 2018  o Reduction of overall heat stress - heat loss through convection by exposing body to air currents. Only humans use sweat glands that produce moisture to cool body o Fulfil the locomotor needs of scavengers, migratory scavengers following ungulate herds, endurance hunters & game stalkers o Allows for better vision in open environments & defensive action against predators by freeing hands to throw objects Efficient Bipedality was not seen until Australopithecus afarensis o Pelvis and leg bones of Australopithecus do not resemble a chimp in any functional way. o Totally humanlike in functional morphology by about 4 million years ago The Valgus angle o Angle of femur to head of tibia is the valgus angle o Valgus angle allows for the feet to be under the centre of gravity o Ape knees have no valgus angle Homo naledi was the first efficient walker o Walked upright o Tiny brain similar to a chimpanzee's o H. naledi may sit between Homo habilis and Homo erectus o Homo erectus was the first efficient runner Survival advantages of bipedalism o Associated with the move from forest to open savannah & more dispersed food resources o More efficient at movement than quadrupeds in this habitat o Improved thermoregulatory efficiency, can forage in heat of day o Improved ability to see and therefore avoid predators o Improved ability to carry food, tools and infants The cost of bipedalism o Backache – our spine is evolved to support hanging weight, not standing weight o Unsupported intestines: hernias. Vertebrate intestines cradled by abdominal muscles. In standing position, intestines hang down onto pelvis. Can pass through cavities in body wall which causes inguinal hernias o Increased pressure on circulatory system. No horizontal element to blood flow as the heart is elevated. Standing reduced cardiac output by 20%. Causes pressure on venous valves in legs and causes varicose veins. Pressure in veins of rectum and anus cause Haemorrhoids o Obstetric dilemma - Narrow pelvis optimal for bipedal walking. Head/body size of infants increasing over time. Baby rotates during birth. Allows head and shoulders to fit through birth canal. Delivered underdeveloped. Humans – 25% of brain developed whereas in chimps – 45-50%. Causes longer developmental time, increased parental care vs other primates Aoife Donohue 2018 Why were Humans more Successful than Chimpanzees? DNA that can be directly compared - 99 % identical DNA insertions & deletions taken into account – 96% identical Cobalamin synthetase is a bacterial enzyme that makes vitamin B12. o Common ancestor to apes incorporated a copy of a cobalamin synthetase gene o Humans are unusual have several copies of cobalamin synthetase-like genes, including one on chromosome 2 o Vitamin B12 is important for brain development and deficiency results in severe neurological defects in human children Decreased birth interval in humans o In mammals weaning generally coincides with first molar (M1) eruption o Infant capable of independent feeding, self-foraging, eat adults type diet o In chimpanzees M1 erupts at 3.1 yrs., chimps delay weaning for a further 2 yrs. Infant learns to acquire and process food, Birth interval delayed relative to M1 eruption o In humans, the M1 erupts at 6 yrs, weaning occurs at 30-36 months o Short birth interval compared to chimps o Trade off early weaning for increased reproduction frequency o Human 3 yr old can’t self-forage or process adult type diet. Digestive system constrained by small stomach and short intestines until ~ 7 yrs of age o Constraints on human infants and children as there is increased energy demanding brain development relative to chimp o This causes co-operative childcare in human societies o Weaned child has special dietary requirements, they need “baby foods” – easily digestible nutrient dense foods o Responsibility of feeding generally spread in humans o In Chimpanzees, 100% of infant care down to mother. There is competition for resources o Females antagonistic to other and their infants o If mother dies, infants rarely survives The Life History Theory Infancy and juvenile stages are common to both humans and chimps but childhood and adolescence are uniquely human. Childhood is needed for increased growth period for brain o Increased quality of body o Size and quality of brain Juvenile to adolescence: o Self-feeding capability (digestive system able for adult foods), o Slowed growth in preparation for sexual maturation o Juvenile period ends with puberty. Aoife Donohue 2018  Adolescence o Growth spurt in height and weight, o Completion of permanent tooth eruption, o Secondary sexual features develop, o Sociosexual maturation (interest in and practice of adult social, economic and sexual activities), o Ends with cessation of bone growth, M3 eruption. Adolescence has been selected for throughout evolutionary history o Childhood evolved to increase maternal reproductive rate o Adolescents help with infants reduces dependence on mother o Increased sibling survival offsets delayed reproduction o Also allows sociosexual maturation Sexual development in Chimpanzees o Oestrous cycle o Sexual swelling advertising fertility o Males most interested during fertile period o Swelling/menarche at 11 yrs, ovulation follows ~2 yrs later. Sexual development in Humans o Menstrual cycle – hidden fertility, cycle not closely correlated with ovulation o Males sexually interested throughout cycle o Menarche at 12 yrs, o Ovulation irregular o Fertility reduced during adolescence. Reproduction during adolescence; o Risks of teenage pregnancy- low birth-weight infant, premature birth, high blood pressure in mother, foetal death and birth complications. o Sexual maturity is linked to pelvic growth- bipedalism selects for bowl-shaped pelvis, bi-iliac width of 24cm needed before menarche occurs, critical birth factor (pelvic size) not reached until 17-18 yrs, first birth typically 19 for humans. o Adolescence in males: Start producing sperm at 13.4 yrs, few males reproduce during adolescence, just starting growth spurt, look more immature than they are, male-male competition. Evolutionary Trade Offs The Vitamin C Pathway Vitamin C (Ascorbic Acid) has many important functions in the body o Essential for formation and maintenance of collagen. Collagen required for growth, health, & repair of bones, tendons, cartilage Aoife Donohue 2018  o Antioxidant, minimizing effects of oxidative stress o Important role in brain function o Involved in synthesis of norepinephrine, a neurotransmitter o Essential role in the synthesis of carnitine which helps convert fat to energy o Enhances absorption of heme iron and is an important element of haemoglobin Scurvy is caused by a deficiency of vitamin C o Early symptoms include malaise and lethargy o Other symptoms include shortness of breath, bone pain, skin changes and emotional changes o Late stage scurvy can cause jaundice, generalised edema, neuropathy, fever, convulsions and eventual death Synthesis pathway present in majority of vertebrates and invertebrates o It is produced in kidneys o Synthesis organ switched twice during evolution o From kidney to liver, once in birds and once in mammals o This was because of a more active/stressful lifestyle o It was required to maintain biochemical homeostasis The evolutionary implications of the loss of the vitamin C pathway: o We must have a vitamin C rich diet o The GLO gene, which codes for the pathway, is under neutral selection. The loss did not result in reduced fitness o With a vitamin C rich diet, there is no selection pressure to regain synthesis o Scurvy only occurs because of changes to the human diet Adapting to High Altitude At such high altitudes, lack of oxygen puts stress on the human body o Hypoxia or a reduced amount of available oxygen in the atmosphere (due to barometric pressure) or to insufficient amounts of oxygen in the body o This condition results from reduced barometric pressure, therefore, there is not less oxygen at high altitudes it is less concentrated o Hypoxia exerts the greatest amount of stress on human physiological systems, especially the heart, lungs and brain There are two types of responses to life at high altitude, genetic / developmental or adult acclimatisation o Adult acclimatisation occurs upon exposure to high altitude in people born at a low elevation o May be short term modifications, but begin within hours of the altitude change o Increase in respiration rate, heart rate and production of red blood cells There are some features that are common to all developmental adaptations Aoife Donohue 2018  o High-altitude natives whose adaptations are acquired during growth and development i.e. they are born at high altitudes o Have a higher lung capacity and are more efficient than migrants at diffusing oxygen from blood to body tissues o Do not rely as heavily on increased red blood cell formation as do newcomers There are two main groups of people who have adapted to life at high altitudes: the natives of the Andean Altiplano and the Tibetan Plateau o The people of the Andean Altiplano have taken the haematological route, they have higher haemoglobin concentrations in the blood but breath at the same rate as those at sea level o The people of the Tibetan plateau have taken the respiratory route, they breath faster that those at sea level and produce more nitric oxide to increase blood flow There are reproductive implications of living at high altitude o Native high-altitude women (genetic adaptation) have heavier babies than acclimatized women o Placenta more vascularised at altitude – higher density of blood vessels (both native and migrants) o Uterine blood flow velocity higher in women of Tibetan descent o Andean women have greater uterine artery enlargement during pregnancy Lactose Intolerance Ancestral human diet, following split from chimps subsistence similar to primates at first o Meat became an increasing component due to scavenging/hunting o Plant resources such as roots/tubers became digestible with development of cooking o Food procurement became gender specific – men hunting, women gathering Change from hunter/gatherer to food production during the Neolithic Revolution o Cereals and cattle quickly replaced the previous diet o Milk only digestible by infants – Gene for lactase enzyme turned off in adulthood – May have assisted in early weaning o Adults became lactose intolerant – causes diarrhoea, Nausea/vomiting, Abdominal cramps, Bloating, Gas o Adults learned to ferment milk and make cheese 8000 years ago in what is now Turkey mutations near lactase gene resulted in lactose tolerance in adults (lactase gene not turned off) Tolerance found in Africa and Eastern Europe o Europe –alternative food source in times of famine o Africa –alternative to contaminated water o Lactose tolerant adults more likely to survive therefore, tolerance increased in population Skin Colour Aoife Donohue 2018  Ancestral condition –pale skin covered by thick fur o Bipedalism improved thermoregulatory efficiency o Less exposed surface area - loss of hair was associated with evolution of sweat gland cooling system o Eccrine glands in the skin produce sweat o Evaporation of sweat cools blood flowing in capillaries under the skin o Evaporation more efficient in the absence of hair, causing hair loss Human skin more resistant to water/abrasion than primates o Epidermal thickness increased o Permanent UV protective pigmentation evolved The Biological determinants of skin: o Haemoglobin has a reddish hue when oxygenated – this produces a pink tint in fair skin o Deoxygenated haemoglobin has a blue tint - Produces the bluish tint to lightly pigmented skin that is characteristic of oxygen deprivation and suffocation o Melanin granules and melanocytes cause the skin to be light or dark. o Eumelanin causes black/brown skin while pheomelanin causes light skin o Melanin is produced by melanocytes in the form of melanosomes. These sit over the nucleus of skin cells to protect them from UV radiation. The greater exposure someone has to UV, the darker their skin o Sunburn is not associated with a change in fitness, so it was not the evolutionary pressure that selected for pale skin Dark skin evolved as folate protection o Folate: water soluble B vitamin acquired from diet o Involved in: o Regulation of gene expression, involved in “silencing” genes - May be involved in risk of developing cancer o Amino acid metabolism - Folate-dependent co-factors break down amino acids o Deficiency results in increased homocysteine in bloodstream. This causes Increased risk of cardiovascular disease o Nervous system development during pregnancy - Deficiency increases risk of anencephaly and spina bifida o Spermatogenesis - Involved in the production of healthy sperm o The selective pressure for dark skin was folate’s importance in nervous system development and spermatogenesis Light skin evolved for vitamin D production o Vitamin D is produced from precursor molecules in the skin that absorb light energy UVB (liver & kidney involved also) o It is important in maintaining normal calcium and phosphorus levels in the blood and in the formation and maintenance of strong bones Aoife Donohue 2018  o Potential to produce vitamin D varies globally. It is supplemented in food in many countries – milk, bread etc Evolution Consequences of living in a sterile world When urban living reduced contact of humans with microbes and worms, it increased our risk for chronic inflammatory disorders We are evolved to come into contact with certain organisms – our immune system is designed to come into contact with disease The old friends hypothesis states that we are dependant on exposure to microbes and other organisms during critical phases of development T lymphocytes play a role in immunity Regulatory T cells recognise our own cells, bring an end to inflammatory response and stop autoimmune diseases o These cells only become effective if stimulated by exposure to certain organisms with low levels of pathogenicity Evidence for the Hypothesis Allergic reactions less likely if you: o Had older siblings, especially brothers o Rarely washed your hands or face as a child o Lived in a home with bacteria‐laden dust o Were brought up on a farm with animals o Had a dog o Had a childhood infection that was transmitted by faecal to oral contamination Exposure to immune challenges at a young age reduces risk of have overeactive responses later in life Organisms relevant to this hypothesis are those that coevolved with humans and other mammals Organisms that must be tolerated Aoife Donohue 2018  o There is no point mounting a new response if it is harmless and if we will just get re- infected Example: Helminth (worm infections) Host-parasite interactions o Parasite needs the host to survive at least long enough to ensure transmission o Parasite needs to survive in host long enough to reproduce Naive body reacts with a strong inflammatory response o Inflammatory responses are damaging o Selection shaped hosts to downregulate this response Host and parasite co-evolved o When parasites removed, relationship disrupted o Immune system responds pathologically Multiple Sclerosis is an inflammatory disease in which the insulating covers of nerve cells in the brain and spinal cord are damaged disrupting the ability of parts of the nervous system to communicate o Patients with MS who are infected with worms either improved or did not get worse in clinical trials. o The host did not have a severe inflammatory reaction to the parasite, thus the inflammatory reaction as part of MS was reduced. Co-evolution Co-evolution occurs when two or more species exert selective pressures on each other and evolve in response to one another. Because each species is evolving in response to the other, one important feature of coevolution is that the selective environment is constantly changing Selective pressure will be strongest when there is a close ecological relationship o Co-evolution can occur between predator and prey, parasite and host, mutualists or competitors o Co-adaptation is the process by which two or more species, genes or phenotypic traits undergo adaptation as a pair or group Co-evolution often occurs between hosts and pathogens. o Resistance is the ability of the host to combat the parasite o Virulence is the ability of the parasite to harm the host There are three possible outcomes when a population is infected by a new agent: o 1. The host’s immune system overwhelms the agent o 2. The agent overwhelms and kills the host without being transmitted o 3. The agent replicates within the host and is transmitted to a new host. The hosts may die or recover Aoife Donohue 2018  New infections may produce a high death rate, but over the course of time the host and agent adapt to one another and the disease normally becomes less virulent o if the host is susceptible, selection favours virulence o This causes selection for resistance in the host, leading to selection for less virulence in the parasite (virulence is costly), leading to selection for less resistance in the host (resistance is costly) Adaptation Adaption arises from the processes of natural selection. Hosts that are genetically more resistant survive in greater numbers to transmit their genes to the next generation Natural selection favours agents that develop mechanisms for successful transmission to a new host. One possibility is to become less virulent so that the host will survive longer. These processes can be best observed in species that reproduce quickly. Myxomatosis in Australian rabbits provides a good example. Populations can be divided into three categories with respect to diseases that confer immunity: o Susceptibles o Infectives o Immunes If a disease is very infectious, a high percentage of the population become infected and either die or survive as immunes. o A high percentage of surviving adults will be immune so children will make up the majority of susceptibles. o Highly infectious diseases therefore tend to become a disease of childhood and may become milder. The population size of the hosts has an effect on the pathogen o Diseases in small populations cannot find sufficient hosts and burn themselves out. o In larger populations the disease may be able to find a continuous supply of new hosts and become endemic – i.e. continuously present. o If the disease is highly infectious but generates immunity, the fresh hosts are provided by non-immune children. o In smaller populations after a disease burns itself out, the nonimmune population gradually builds up and may become infected from outside to produce an epidemic. o An epidemic on an inter-continental scale is called a pandemic Host –pathogen coevolution in human tuberculosis Tuberculosis (TB) o Common, potentially lethal infectious disease o Caused by strains of mycobacteria Mycobacterium tuberculosis Aoife Donohue 2018  o Tuberculosis typically attacks the lungs, but can also affect other parts of the body o Spread through the air when people who have an active TB infection cough or sneeze o Most infections are asymptomatic and latent o One in ten latent infections progresses to active disease o Untreated, kills more than 50% of those infected TB is a disease long-associated with humans. Many pathogenic viruses, bacteria and protozoa evade host immunity by varying their antigenic genes. Ensuing host immune responses contribute to tissue destruction and the formation of cavities in the host lung, which ultimately enhances transmission Coevolutionary history of TB with humans o Most evolutionary history occurred during hunter–gatherer times o Human population densities were low o Characteristic latency period of TB, followed by reactivation and active disease several decades later o Might have evolved to allow TB access new cohorts of susceptible hosts o Avoid a burn-out situation whereby all susceptible hosts would be decimated by an overly virulent pathogen o High host densities similar to the ones encountered in the crowded cities of eighteenth and nineteenth century Europe, might have selected for less ‘prudent’ forms of TB, as access to susceptible hosts was no more a limiting factor o ‘Modern’ TB is more virulent and associated with a shorter latency period compared with ‘ancient’ TB TB has become a threat again o Unique characteristics give it enormous potential for developing resistance to even the strongest antibiotics o TB combines one of the slowest division rates among bacteria with a hardy cell wall defence system Mating Patterns Notes Sexual Selection Darwin’s theory of sexual selection states that sexual selection “depends on the advantage which certain individuals have over other individuals of the same sex and species in exclusive relation to reproduction” Sexual selection can operate through two mechanisms: o Intersexual selection: competition between members of the opposite sex (females choose attractive males, Male sexual proprietariness ) Aoife Donohue 2018  o Intrasexual selection: competition between members of the same sex (Males competing with each other for access to females) Intersexual selection is obvious in the Wodaabe clan in Chad o Tall and athletic: Ostrich plumes and pompoms emphasise height o Narrow face: Decorated with red ochre o Wide eyes: Black eyeliner made from charred egret bones o Facial symmetry: Enhanced with black, yellow and white patterns o Aquiline nose: White clay arrow stripe to look more streamlined o Long braids and cowrie shells: Symbolise fertility and wealth o White and regular teeth: Bared and emphasised with black lipstick o Good dancer: Beaded necklaces and bodices jangle against chest in time to the beat Selective male choice o Satin bower birds collect blue objects to impress the females o This is also obvious in humans, eg. Presenting flowers Intrasexual selection o Deer - Stags fighting during the rutting season. The creation and maintenance of 'dominance hierarchies' o Humans. The tendency of young men to engage in risk taking and intermale aggression. Female obsession with fashion and looks Parental investment and sexual selection Parental investment - Sex that invests greater resources in offspring will evolve to be the choosier sex in selecting a mate o Sex that invests fewer resources in offspring will evolve to be more competitive with its own sex for access to the high-investing sex o Females – manufacture eggs, incubate foetus, post-partum care, loss of mating opportunity o Males limited by the number of successful matings – manufacture sperm, parental care Female Choice models Direct benefits o Females have a predisposition to choose males that provide them with tangible resources eg. food, shelter, assistance with parental care etc Good genes o Females choose mates with “good genes o Genes which code for favourable traits o Indirect benefits model o Offspring inherit these “good genes” They look for certain criteria: Aoife Donohue 2018  o Physical Features: size and strength which confer dominance and so preferential access to resources o Behavioural Features: may indicate willingness to invest or good parenting skills Females will compete with other females for the right to choose the most desirable (alpha) males o Compete in traits/qualities males find attractive o Gain little from multiple matings and seek quality not quantity Male Reproductive Strategy Males are far less choosy as they as they little to lose and everything to gain if they can have as many mating opportunities as possible o Males are not tied to rearing offspring and so seek quantity o While they would prefer a superior female, they are less choosy o If presented with a sexual opportunity they will take it o Males compete vigorously with other males for access to fertile females o Male reproductive success is however very variable, a small number of males will achieve many matings, while many males may never mate Mating Systems Polyandry – numerous males and one female Monogamy – one male and one female Polygynandry – numerous male and numerous females Polygyny – one male and numerous females Degree of male-male competition in a species generally related to degree of sexual dimorphism o Men have larger stature, more robust facial features, Greater muscularity, strength and speed Evidence for monogamy o Highly altricial - Prolonged childhoods, reliance on family throughout life spans o Designed for romantic pair bonds - Dedicated neurochemistry of attachment associated with monogamy Evidence for promiscuity o Psychological and physiological adaptations to sperm competition o Women’s adaptive timing of extrapair copulations o Men’s specialised expression of sexual jealousy o Human penis designed as a sperm displacement device o Sex with multiple partners often viewed as desirable among men o Ejaculate variations is determined by how long the partners have been apart o More blocker sperm is produced if the partners have been apart Aoife Donohue 2018  o Coronal ridge evolved to displace semen from the female reproductive tract, deposited by other males Evidence for polygyny o Sexually differentiated life history not seen in monogamous primates o Men are more physically aggressive, Men die earlier/younger, Men mature later than women in all cultures Humans equipped with specialised mate choice adaptations for both long term mating (marriage and long-term fidelity) and short term mating (promiscuity and infidelity) Flexible mating design would have provided important reproductive benefits to humans in out ancestral past, allowing individuals to functionally respond to a wide range of familial, cultural and ecological contexts Men and women seek different qualities in their long-term partners o Women - More emphasis on men’s status, resources, ambition and maturity. Clues relevant to ability for long term provisioning/parental care o Men - More emphasis on signals of fertility and reproductive value. Women’s youth and physical appearance Short term mating o From a parental investment perspective, women benefit little from short-term sex with multiple partners. More likely to engage in short term mating with high quality male o Men are more interested in having a variety of partners. Consenting to sex sooner with a new partner. Seeking short term mating opportunities than females The Operational Sex Ratio determines the reproductive behaviour o There are typically more males available for reproduction at any one time o Lower sex ratio (more women than men) - Short term orientated mating strategies. short term mating strategies. Increase in divorce rates & reduction in female ‘sexual coyness’ o High sex ratio (more men than women) – More competition between men for available women. Increasing monogamy - Lower divorce rates & increased paternal parental investment Other elements of Mate Choice Inbreeding avoidance o Inbreeding depression: reduced fitness of inbred individuals that results from the expression of deleterious traits o More closely related individuals are, the more homozygous the offspring, higher risk of recessive deleterious mutations being expressed o First cousin marriages common in some cultures – 5% increased probability of child not reaching 10th year of life. If siblings, risk increased by 20-25% Aoife Donohue 2018  The Westermarck effect allows us to avoid inbreeding - Men and women raised together are usually not sexually attracted to each other, regardless of whether they are genetically related or not Evidence o Children raised communally in an Israelian kibbutz almost never marry o Females in particular less tolerant of sexual advances by males they grew up with o Has an olfactory basis o The MHC (Major Histocompatibility Complex) is a large chromosomal region containing genes that play a role in immunological self/non-self recognition o Female rodents learn the MHC identity of their relatives during development via pheromones, and prefer to mate with males who carry dissimilar genes o MHC can be used as a signal of possible relatedness o MHC assessed through body odour o Prefer the body odour of MHC-dissimilar individuals o Couples were less likely to share MHC-haplotypes than chance; in couples who had similar MHC genes they had more fertility problems (unconscious avoidance of inbreeding?) o People seem to select perfumes and deodorants that enhance their own body odours to reveal their immunogenetics Imprinting and Mate choices o Sexual imprinting in humans o Children shape a mental template of their opposite-sex parents and search for a partner who resembles their opposite sex parent between the ages of two and eight years o Depends on the emotional warmth in the relationship with the father Sexual imprinting in humans results in a preference for intra-cultural (same culture) marriages o Can lead to increased disease risks if a recessive gene is endemic to a culture o Cystic fibrosis in European cultures o Thalassemia in Mediterranean cultures o Tay – Saches disease in Jewish cultures o Hereditary hemochromatosis among Celtic cultures Genetics Genetics is the scientific study of heredity and hereditary variation Genes are coded information passed to offspring in hereditary units. Genes usual contain the genetic code for proteins Karyotype is a method of organising the chromosomes of a cell in relation to number, size and type. Homologous chromosomes are chromosomes that make up a pair, with similar length, centromere position, and staining. They possess genes for the same traits Aoife Donohue 2018  Sex chromosomes are chromosome that determine the sex of an organism. Autosomes are all other chromosomes DNA is conserved throughout all organisms o It is the hereditary material for almost all life o Chargaff’s rule states that %A=%T in a cell and %G=%C in a cell Comparative Genomics Mutations in the genetic code Point mutations are changes in one base pair of a gene. If the mutations are in gametes, they can be passed on to offspring Wild-type genes are the most common alleles in the population Types of point mutations o Silent substitutions have no effect on the overall protein produced o Missense mutations cause the mRNA to code for a different amino acid o Nonsense mutations cause the stop codon to be coded for prematurely o Deletions can cause a change in reading frames causing a change in the amino acid sequence o An insertion has the same effect as a deletion o An insertion or deletion of three nucleotides can cause an amino acid to be added or missing from the final protein Comparative Genomics Comparative genomics enables us to understand how our own genome functions and how we evolved Some genes are conserved throughout evolution. Mutations in evolutionary conserved areas will not be tolerated. The Human Genome Project The aims of the human genome project was to: Map and sequence the human genome o Build genetic and physical maps spanning the human genome. o Determine the sequence of the estimated 3 billion letters of human o DNA, to 99.99% accuracy. o Chart variations in DNA spelling among human beings. o Map all the human genes. o Begin to label the functions of genes and other parts of the genome. Map and sequence the genomes of model organisms o The bacterium E. coli o The yeast S. cerevisiae Aoife Donohue 2018  o The roundworm C. elegans o The fruitfly D. melanogaster o The mouse M. musculus Collect and distribute data o Distribute genomic information and the tools for using it to the research community. o Release all sequence data that spans more than 2000 base pairs within 24 hours. o Create and run databases. o Develop software for large-scale DNA analysis. o Develop tools for comparing and interpreting genome information. o Share information with the wider public. They made physical and genetic maps using shot gun sequencing o Shotgun sequencing is quicker than using physical and genetic mapping o Shotgun sequencing works by sequencing small isolated regions of DNA and then putting them together by finding out what overlaps The first draft of the human genome project was released in 2001 and it was completed in 2003 o It estimated the number of genes and the percentage of genes which code for proteins Annotating the genome o Find the coding regions ie start codon AUG followed by a stop codon later? o RNA splice sites o Compare the DNA code to mRNA o Compare the genome structure between different animals The Tree of Life Longevity By studying other organisms, we can uncover the molecular mechanisms that enable mammals achieve extraordinary longevity We can cure ageing by reducing the build up of damage in cells Telomeres contribute to aging by getting shorter as we age o Every time a cell replicates divides, the telomeres get shorter o Eventually they become so short they signal that the cell needs to be removed because the DNA cannot replicate anymore o Bats can maintain telomeres length without expressing telomerase (telomerase lengthens telomeres but causes cancer) o The genes ATM, SETX and MYC might allow then to lengthen telomeres – alternative telomere lengthening As we age, we become inflamed Aoife Donohue 2018  o Could powered flight, extraordinary immunity and extended lifespans be caused by the immune system? o Because flight is so metabolically costly, the broken bits of mitochondria cause an inflammatory immune response. The bats can dampen this immune response. o This might allow them to live longer as they have less age-related inflammation. Phylogenetic Trees Depicts the past evolutionary relationships between two species Cladograms show branching order, but branch lengths are meaningless Phylograms show branching order and branch lengths are drawn in relation to time We can examine how we are related to other organisms by reading a phylogenetic tree We are a member of class Mammalia o Subclass Prototheria: includes platypuses. They lay eggs but still produce milk o Subclass Theria: includes infraclass Metatheria (marsupials) and infraclass Eutheria (placental mammals - us) o We are in the order Primates Traditionally researchers would compare morphological characters: shape of teeth, length of bones, structure of skull and use these characteristics to create a phylogenetic tree o This is not accurate because of convergent evolution o Humans were considered to be closely related to tree shrews, flying lemurs, bats o We were placed in the Super Ordinal Group Archonta Two famous research papers that compared the DNA ‘spelling’ from genes sequenced from divergent mammals to create a phylogenetic tree o This rewrote the phylogenetic tree o Animals that had an A at the same point in a gene were considered to be more closely related to each other than animals that had different nucleotides at the same point o We are now in the order euarchonta Morphology was not able to reconstruct the tree o The change in morphology was so rapid around the time of the death of the dinosaurs that there is not fossil evidence to support the changes Because the tree is now based on phylogenetic data, we can date divergences in the tree o This was not possible with morphology as it relied on fossilised evidence When did the diversification of mammals occur? o Before the death of the dinosaurs o There was a massive change in genetics, but not necessarily in morphology We can try to discover the cure for diseases by researching other organisms who are immune to the diseases o Cheetahs are so genetically identical that they do not reject skin grafts from other cheetahs Aoife Donohue 2018  o They rejected skin grafts from domestic cats, showing that their immune systems do work o As the population gets smaller, we lose genetic diversity. o They have very poor immune systems Aoife Donohue 2018