Primate Evolution PDF

2: the adaptive traditions of the primates Geological epochs MYA Pleistocene 2 Pliocene 5 Miocene 24 Oligocene 37 Eocene 58 Paleocene 65...

2: the adaptive traditions of the primates Geological epochs MYA Pleistocene 2 Pliocene 5 Miocene 24 Oligocene 37 Eocene 58 Paleocene 65 - The earliest primates were “squirrel-like” in shape - From the original form, the primates multiplied in number to reach today about 200 species What happened 65 million years ago? Three scenarios 1. Aboreal theory: theory stipulating that primates are what they are because they adapted to a physical environment called “tree living.” 2. Visual predation theory: primates developed adaptions that permitted them to catch insects on tree branches/ it is about a course of foods 3. Angiosperm radiation theory: primates adapted to feeding on all kinds of small objects in the same arboreal habitat (flowers, fruits, gum and nectars) primates: different evolutionary grades - Although life forms change over geological times, it is nonetheless possible to gather a rough picture of the evolutionary past forms by looking at currently living forms - thus, living primates still display all the major levels of organization they went through during the last 60 million years Definition: “evolutionary grade”; a group of animals with similar levels of organization Three grades in primate evolution 1. Prosimians: retained many features of the common primate ancestor 2. Monkeys 3. Apes were most transformed when compared to the common primate ancestor Primitive condition: a species that looks very much like its ancient ancestors because it has evolved very little Derived condition: a species that is quite different from its ancient ancestors because it went through a lot of transformation Survey: the prosimians - 70 species alive (over 200 extinct) - Two main species - Lemurs and lorises Key concepts: adaptive radiation Definition: “Adaptive radiation”: the multiplication of the number of species in a short geological period. Two main causes: - When an adaptive zone is left empty, the extinction of dinosaurs 65 MYA opens the door to mammals. - When a new evolutionary trick is found: the invasion of lands by “walking” and “air-breathing” animals 360 MYA. Key concepts: speciation - The concept of “adaptive radiation” is a descriptive one: it does not explain how species actually split. Definition: Speciation or slitting of species: the evolutionary process that produces new species from the previous one. Missing concepts: biological species concepts Define: “biological species concepts” - Species are groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups.  Anagenesis: transformation without splitting Cladogenesis: transformation by splitting Adaptive radiation versus speciation - A speciation can occur without an adaptive radiation - because the splitting of one species into two species does not involve enough diversification of forms to be called “adaptive radiation.” - The reverse, however, is not true. Adaptive radiation cannot occur without speciation for - by definition an adaptive ratio is a cascade for speciation occurring in a short periods. Prosimians versus anthropoids 1. Larger body size 2. Larger brain size 3. More rounded skull 4. Eyes completely in front of the skull 5. Complete back wall to eye orbit 6. Only two incisors on each side in both jaws 7. More complex social systems 8. More parental care Monkeys - 140 species (70 extinct) - Two main groups: new worlds and old world monkeys New World monkeys: - Distribution: central and south America\ - Three premolars (old-world monkeys and apes have two premolars) - Prehensible (grasping) tail Species: - Howling monkeys - Tamarins - Woolly monkeys - Black spider monkeys Old world monkeys: - Distribution: a big part of Africa and South Africa - Dental formula 2:1:2:3 - 2 incisors - 1 canine - 2 premolars - 3 molars Species - vervet monkeys - Macaques - Cercopithecus Old-world and new-world monkeys have this body type. Hypothesis 1: common ancestry Hypothesis 2: evolutionary convergence Similar adaptive (selective forces) - owing tropical arboreal environments both in the old worlds - led to anatomical or structural evolution in somewhat different but parallel directions. Hypothesis 3: adaptive versatility - Given the very versatile and efficient biological organization of the monkey “architecture,” this type would have been under a relatively weak action from natural selection. - Therefore, there would have been little reason to go through profound modification. - Sometimes, life forms hit upon the right body type, requiring little changes over time. - Scorpions have not changed much in 250 million years. - Apes: small adaptive radiation on the fall. - 14 species alive today - 1 human - 2 chimpanzee - 1 gorilla - 1 orangutan - 9 gibbon - This is reflected in their limited geographical distribution Confronting the reality of extinction Prosimians 70 alive 200 extinct Monkeys 140 alive 72 extinct Apes 14 alive 65 extinct Diversified ape radiation: the gibbons - Distribution: Southeast Asia - No sexual size dimorphism between males and females - Monogamous families - Single birth every four or five years - Mode of locomotion: brachiation Orangutans - Distribution: island of Borneo ans sumatra - Extremely sexually dimorphic species: females (60kg), males about twice the weight Cranial feature 1. A relatively high, rounded braincase 2. Poorly developed brow ridges 3. A deep face with samm orbits set close together 4. A uniquely prognathic snout with a large convex premaxilla 5. The mandible has a high ascending ramus Two key muscles: masseter muscle and temporal muscles Gorillas - Distribution: Central Africa - Largest living primate: females (70-90kg) and males (200kg) - dimorphism reflected in cranial anatomy - Caine size - Sagittal and nuchal crests - One-male group: +/- 9-20 females offspring - Most terrestrial of all the primates - Knuckle walking Chimpanzees - Distribution: in Africa from Senegal, Tanzania - Occupy a variety of habitats, from rain forest to dry savanna areas with very few trees - locomotion: Kunkle walking - Complex behaviour: - Hunting patterns (males) - Tools: leaves as sponges, twigs as probes, stones to smash nuts - Fusion-fusion societies - Males are gregarious; females are more isolated around their offspring A diversified ape radiation: Humans Distribution: nearly worldwide Body proportions: very long legs, upright pidedal gait Opposable thumbs Naked apes Cranial anatomy: ○ Large rounded cranium with a large brain ( 3 times that of other apes) ○ Small canines ○ Gracile mandible with a very unusual protruding chin Diet omnivorous; anything goes 1. Prosimian like grade: palecone/ early eocene Environmental context: densely forested areas in the context of warm and humid tropical climates Geographical distribution: North America, Europe, south Asia and Africa Behaviour: acrobatic locomotion (leaping ability) anatomy: limb proportions: long legs relative to short arms 2. Primitive anthropoid (monkey/apes) grade: early Oligocene  Enviromental context: dense forest areas in the context of warm and humid tropical climates but somewhat seasonal Geographical distribution: South America, Africa, and South Asia behaviour: development of adaptions for spending more time walking on top of branches anatomy: limb proportions: fairly short, similar- length forelimbs and hindlimbs.  3. Ape-like grade Miocene (25- 5 MYA) Environmental context: trend towards cooler, drier, more seasonal continental climates (spread of woodlands and savannas at the expense of forest) Geographical distribution: Europe, Africa (east Africa), and South Asia Behaviour: erectness of the upper body, suspensory locomotion (hanging) Anatomy: limb proportions: short hindlimbs and long forelimbs anatomy: from small to large body size (3.5 to 50kg) Ancestors of living apes: Gibbons: possibly pliopithecus dated at 15-11 MYA (small size; short snout; large orbits) Gorilla: no clue Chimpanzees: no clue Orangs: good candidate in sivapithecus at 10 -8 MYA Human: plenty of potential candidates Tooth morphology: clues about behaviours Three complexes: 1. Frontal teeth (incisors): the first stage of eating by breaking into the food 2. Canines: 3. Back teeth (molars/premolars): the second stage of eating by crushing food Teeth morphology Insect eaters: molars and premolars teeth with sharp cusps and very well-developed shearing crests useful for breaking up insects skeletons which can be hard. Common among prosimians Gum eaters: specialized incisor teeth forwardly projecting (dental comb) for digging holes in bark. It's not rare among prosimians. Left eaters: small incisors (leaves require incisive preparation) and molar teeth with well-developed shearing crests but somewhat rounded cusps useful for breaking up through fibrous leaves. Common among monkeys/apes Fruit eaters: relatively large incisors for ingesting fruits (the bite in the fruit) and simple molar teeth with low cusps for crushing and pulping soft fruits. Common among monkeys/apes How about canines? Although canines play a part in processing food, these are not strongly. Canine morphology: Polygany Males living in a polygamous group: large canines Females living in a polygamous group: small canines Monogamy Males living in a monogamous group: medium-sized canines Understanding humans evolution: additive and complementary sources of information 1. Evolutionary biology(concepts): divergence, speciation, biological species concepts, 2. geology (the study of the past): established of the geological periods: paleocene, Eocene, Oligocene 3. Biogeography (the study of the geographical distribution of life forms) 4. paleoenvironment(the study of ancient climates) 5. Ethology ( the study of behaviours among the living forms) 6. Anatomy (the study if morphology in living and extinct forms ) 7. Socioecology (the study of variations in social organizations) Humankind's closest living relations: On the basis of morphology, it is clear that humans are more closely related to the great apes, but with humans being more distant within the groups. ○ Orang ○ Gorilla ○ Chimpanzee School of Phonetics: Phylogenetic analysis based on overall similarities and differences Principle: species sharing a greater number of similarities are assumed to be more closely related than species sharing a smaller number of similarities Evolution playing tricks on us: 1. Two species may look alike because they share a common ancestor 2. Two species may look alike because they have developed similar adaptations - This is called “evolutionary convergence” or “convergent evolution.” 3. Two species may not look alike, although they do share a recent common ancestor - This is called “evolutionary divergence” or “divergent evolution.” Question: is there a better method than taking into account overall similarities/differences in phylogenetic analysis Question: can we disentangle the mixed singles - Similarities owing common ancestry - Similarities owing to similar adaptions Two competing schools: Schools of phenetics (or pheneticists) Phylogenetic analysis based on overall similarities/differences All the features are treated equally. A quantitive approach: comparison without discrimination of as many traits as possible Based on overall similarities/differences Schools of cladistics (or cladists)  Phylogenetic analysis making a discrimination by distinguishing between “primitive” and “derived” features Some features are excluded from the analysis. Species D and E are more closely related not because they share more traits in common ( as argued in phonetics); but because the characteristics they share (four cusps) are indicative of splitting sequence, allowing us to deduce the existence of more recent common ancestors to the exclusion of other species. In a qualitative approach, traits are selected or weights, looking for more revealing features. Based on a distinction between “primitive” versus “derived” features Part II Humankind’s closest relatives Complementary: scientific disciplines often provide coherent and consistent information. Contradictory: scientific disciplines sometimes offer incoherent information. - In this case here, “morphology” versus “molecules.” Ramapithecus: 5 key features 1. The canine teeth were short, in contrast to the long canines of apes. 2. The snout is reduced (short face), and so are all the anterior teeth (premolars, canines, incisors). In apes, the snout projects forward, and the anterior teeth are large. 3. The enamel cap on molars is thick, as in humans, while chimpanzees and gorillas have thin enamel. 4. The cheek teeth - the molars- were very likely those in modern humans. The surface did not protrude as it does in apes. 5. The dental arch- as reconstructed- was parabolic as in humans and u-shaped as in apes. Rampithecus: form morphology to behaviour Influenced by charles darwin descent of man (1871), the discovery of ramapithecus assumed the following: ○ Bipedality ○ Freed hand ○ Reduced canines ○ Manufacture of tools ○ A big brain - They discover they are the same thing The traditional view: morphology After the fall of Ramapithecus, no more fossils could be used to support the traditional view. ○ Although the facts based on living on the morphology remained Then came the rise of a new scientific discipline: molecular biology ○ An alternative view was proposed Problem: Morphological changes of the phenotype are not perfectly reflected in the genetic changes if the genotype. ○ In other words, living organisms are so complex that there is a mismatch between what we see of them (morphology/behaviour) and the genes they carry genotype/phenotype: why After all, it seemed logical to assume that when you see changes in the morphology/behavior of an organism, it must be because the gen of the organism are changing too, no? Only genes of organisms are being transmitted in the time dimension (generations) yet natural selection chooses them by working through visible features (morphology, behaviour)...NO. Classical genetics: three sources of variations 1. Sexual reproduction: males and females contribute 50% of the genetic information 2. Recombination: each time a male or female contributes a sex cell for reproduction (sperm or ovule), the genetic information is not always identical. 3. Mutation: a plain biochemical defect in the copying process of sex cells Tight link: genotype/phenotype On the basis of the view of evolution just presented, evolution was not so long ago simply seen as a two-stage process. 1. Production and redistribution of variation through mutation, recombination and sexual reproduction 2. Natural selection acts on this variation to adapt species to changing conditions.  After a few generations (two, three, four), it was expected that genetic variations would be expressed at the phenotypic level. The big surprise: “ neutral theory of evolution.” A lot of genetic changes (mutations) are occurring at the level of the genotype without finding their way to the higher level of phenotype. By not finding their way at the phenotype level - by not being expressed - such genotypic changes are simply invisible to natural selection. ○ These are called natural mutations. Neutral theory of evolution Lower biological levels are somewhat buffered from the direct impact of natural selection: ○ Why? Because some changes are functionally equivalent at these lower levels, creating no impact on the expression of traits at the higher levels. Various levels of evolution: The relative impact of natural selection on each of them If natural selection cannot play a part in choosing some biological features in the lower levels, it is to be expedited that biological variability will be greater at such lower levels Thus, it explains the confrontation between “morphology” and “molecules”: two sources of information. Confrontation Traditional anthropology Molecular anthropology - Studying the phenotype - Studying the genotype - Morphology - Genes - Behaviour - DNA - Fossils - Proteins - Amino acids Molecular anthropology: molecules Phylogenetic proximity: gorillas and chips are more closely related to humans, with organs being more distant comparing the molecules. ○ Humans versus gorilla/chimps: 1-2% difference ○ Humans versus orang 4% difference difference ○ Humans versus baboons: 8% difference  Timeframe: human and the African great apes (gorilla + chimps) shared a last common ancestor some 5 MYA Molecular clock: the logic Once a species had split into two separate species, neutral mutations would accumulate independently and at a steady rate in the gene pools of the two new species, as postulated by the neutral theory of evolution. Differently stated: because some mutations are invisible to natural selection by not being expressed at the phenotypic level, it is possible to use them as a way to count the time that has elapsed since the moment two species separated from common ancestry. Allan Wilson and Vincent Sarich (1967) explanation: 1. They knew that the genetic distance between humans and the African great apes is about one-sixth that of the distance between humans and old-world monkeys. 2. They know that old-world monkeys departed from the group which gave raise to the African great apes and humans some 30 million years ago - This date was provided by the fossil record and was arrived at the standard dating methods - Its logical to assume that humans, chimpanzees and gorillas departed from thei common ancestor 5 million years ago, if the genetic change in all those primate species reminded constant - If it took 30 MY to accumulate the genetic difference between humans and old world monkeys, how long it took to accumulate ⅙ of the difference? Answer 5 MYA - Today, we know that the figure is somewhere between 5 to 8 MYA Molecular clock: the logic Once a species had spilt into to separate species, neutal mutation would accumulate independently and at a steady rate in the gene pools of the twp new species as postulated by the neutral theory of evolution Differently stated: because some mutation are invisible to natural selection by not being expressed at the phenotypic level, it is possible to use them as a way to count the time that has elapsed since that moment two species separated from a common ancestor human/African great apes Two lines of evidence Negative evidence: lack of fossil evidence. Since the fall of rampithecus no fossil evidence can