Lecture 2: Intro to Evolution - A Darwinian View of Life

Lecture 2 Intro to Evolution: A Darwinian View of Life Chapter 22; Ch 23 pages 537-38. It is not the strongest of the species that survives, nor the most intelligent...

Lecture 2 Intro to Evolution: A Darwinian View of Life Chapter 22; Ch 23 pages 537-38. It is not the strongest of the species that survives, nor the most intelligent that survives. It is the one that is most ADAPTABLE to change. - C. Darwin https://www.youtube.com/watch?v=6yEX_OI0xbQ  Darwin: On the Origin of Species 1) Today’s organisms descended November 24, 1859 from ancestral species that were different from modern species. Evolution explains life’s unity and diversity 2) Natural selection is the MECHANISM for this evolutionary change. Natural selection results in adaptive evolution – The basic idea of natural selection is that a population can change over time – Descent with modification  Scale of Nature & Classification of Species The Greek philosopher Aristotle – Viewed species as fixed and unchanging – He concluded life-forms could be arranged on a ladder scale of increasing complexity “scala naturae” (scale of nature) – Each life form, perfect and permeant had its allotted rung on this ladder – Aristotle’s ideas were generally consistent with the old testament account of creation. Holds that species were individually designed by God and immutable (do not change). Carolus Linnaeus – a founder of taxonomy, grouping similar species into increasingly greater categories – Did not attribute resemblances among species to evolutionary kinship, but rather to the pattern of their creation The Method & Process of Science The idea of evolution was around before Darwin…. Lamarck & Evolution - Jean Baptiste de Lamarck: Proposed a theory that organisms evolved over time (evolution!) - By comparing living species with fossils, he found several lines of decent, from older, to younger fossils Jean-Baptiste to living species. Lamarck 1744-1829 - He explained this “change” over time using two principles: 1: Use and disuse 2: Inheritance of acquired traits Lamarck's idea: evolution would drive organisms toward greater complexity and perfection over time Although ultimately incorrect, he did recognize that environment can influence organisms and give rise to evolution.  The scientist is not a person who gives the right answers, he is one who asks the right questions. - Claude Levi-Strauss Studies that helped to lay the groundwork for Darwin’s ideas: The Study of Fossils o Fossils are remains or traces of organisms from the past o Fossils within layers of sedimentary rock show that a succession of organisms have populated Earth throughout time. o Sedimentary rock → determine sequence of events (old = bottom, upper = younger) French scientist G. Cuvier (studied fossils) noted that the older the strata, the more dissimilar the fossils from modern life. He also noted that from one layer to the next, some new species appeared while others disappeared. Inferring that extinctions must have been a common occurrence in the history of life! BUT he opposed the idea of evolution, instead he advocated catastrophism; speculating that boundaries between strata were due to local floods or droughts that destroyed the species present. This idea fit in well with religious teachings. Influence on Darwin’s Thinking: Essay on the Principle of Population by Thomas Malthus Darwin's thinking was also influenced by a publication by Malthus Malthus, in his book Essay on Population (1798) noted that populations grew faster (geometrically) than their food supply (arithmetically). This disproportion between these two powers of increase led Malthus to infer that reproduction must eventually be checked He argued that famine, war, and disease will limit population growth, especially among the poor. An important message from Malthus's work was that only a fraction of any population Malthusian catastrophe will survive and reproduce. Influence on Darwin’s Thinking: Artificial Selection - Humans have modified a variety of domesticated plants and animals over many generations by selecting individuals with the desired traits as breeding stock. - breeders and farmers developed many varieties of domesticated animals/plants in just a few generations Over 14,000 years humans have 'designed' some 400 breeds of domestic dog  Artificial Selection If artificial selection can achieve so much change in a relatively short period of time, Darwin reasoned, then natural selection should be capable of considerable modification of species over thousands of generations. Influence on Darwin’s Thinking: Video textbook resources Hutton & Lyell: Geological data Hutton and Lyell (geologists) suggested that profound change can take place through the cumulative effect of slow but continuous processes (i.e. valleys formed by rivers wearing away at rocks) and that these mechanisms are still operating today and are constant So…. 1) If geologic changes result from SLOW, CONTINUOUS PROCESSES rather than sudden events, then the Earth must be far older than the 6,000 years estimated by biblical inference. (Earth not young & static – which was the tradition view at the time) 2) Slow and subtle processes persisting for long periods of time can also act on living organisms, producing substantial change over a long period of time. These new ideas exerted a strong influence on Darwin’s thinking Review: Darwin’s background information (science) + observations that lead him to develop his hypothesis, predictions... theory of natural selection  Darwinian Evolution Darwin’s voyage was the basis for his theory of evolution Voyage on H.M.S. Beagle (1831): 5-year exploration of South America and the South Pacific Darwin observed various adaptations of plants and animals that inhabited the many diverse environments He saw that Plants and animals in the temperate regions of South America more closely resembled the species of the tropical regions of South America than the corresponding species of the temperate regions of Europe. Being a scientist he was curious about this and wanted to find an explanation….  Collected lots of DATA! Galapagos Islands Darwin was fascinated by the unusual organisms found He hypothesized that the islands had been colonized by plants and animals from the mainland that had subsequently diversified on the different islands. Observed many examples of ADAPTATIONS! inherited characteristics of organisms that enhance their survival and reproduction in a specific environment. For example, clear differences in the beaks among the 13 species of finches that Darwin collected in the Galapagos are adaptations to the specific foods available on their home islands. Proposed that new species arise from an ancestral form by the gradual accumulation of adaptations to different environments  On the Origin of Species... 1840s, Darwin wrote a long essay on the origin of species and natural selection, but he was reluctant to publish and continued to compile evidence (data) to support his theory. 1858, Alfred Russel Wallace (1823–1913), a young naturalist working in the East Indies, sent Darwin a manuscript containing a theory of natural selection essentially identical to Darwin’s. Darwin quickly finished On The Origin of Species and published it the next year. While both Darwin and Wallace developed similar ideas independently, the theory of evolution by natural selection is attributed to Darwin because he developed his ideas earlier and supported the theory much more extensively. How Evolution by Natural Selection Works in 4 parts: 1) Overproduction of offspring 1. Species can produce more offspring than environment can support – For any species, population sizes would increase exponentially spores However, populations tend to be stable in size  2) Availability of Resources / Competition ENVIRONMENTAL RESOURCES ARE LIMITED Production of more individuals than the environment can support leads to a struggle for existence among individuals of a population, with only a fraction of their offspring surviving Organisms compete for limited resources: Food, Water, Light, Space…. Or killed by predators, disease, unfavorable environmental conditions  3) Variation in Population Genetic diversity enables species to adapt to environmental change. Members of a population vary in their characteristics – No two individuals are exactly alike These differences and similarities are because of many small differences between individuals’ genes. GENE: A section of DNA that codes for a trait. All organisms have DNA, and everyone's DNA is organised into genes. These contain the instructions to build our bodies. Differences in DNA affect what individuals look like. Ex. blue eyes to green, or a butterfly’s wings from black to white The combined differences in the DNA of all individuals in a species make up the genetic diversity Genetic diversity causes individuals to have different characteristics, For NS to wok, VARIATIONS that are selected for must be ARE HERITABLE  4) Differential Reproductive Success / Selection -> Adaptation Unequal ability of individuals to survive and reproduce Individuals with beneficial adaptations are more likely to survive to pass on their genes (Survival of the Fittest) Fitness or “Darwinian Fitness”: Ultimately boils down to an individual’s reproductive success. The more surviving offspring an individual produces, the higher its fitness will be. Individuals whose inherited traits give them a high probability of surviving and reproducing are likely to leave more offspring than other individuals Leads to a gradual change in a population, with favorable characteristics accumulating over generations (leads to adaptation) How Natural Selection Works: ❖ Individuals within a population must differ for at least one given trait (variation in populations) If every individual in the population is the same (clones) or identical for that trait, natural selection cannot work and therefore the population cannot evolve. ❖ The variation must be heritable (coded by and passed on to progeny through DNA). Some of us differ due to environment: we dye our hair, work out, loose a limb due to injury, get plastic surgery. Only traits that are heritable (coded by your genes) can be the target of natural selection. How Natural Selection Works: ❖ In any given environment, some individuals within the population will have traits that give them a little advantage. These traits allow them to live longer and more importantly have more offspring. Generation 1 The individuals who’s traits allow them to live longer and have more offspring are said to be “fitter” than Generation 2 those who do not. Fitter individuals have traits that make them better adapted to the current environment and they pass Generation 3 on these traits to their offspring. Natural selection acts on individuals. Populations evolve. Individuals do not.  Mechanism of Natural Selection: Darwin called the mechanism of evolutionary adaptation natural selection because the natural environment selects for the propagation of certain traits among naturally occurring variant traits in the population Evolution has two linked processes: “Environment 1) Random selects” The generation product of natural variability selection is the increasing 2) Selection of ADAPTATION of “suitable” organisms to their characteristics environment. “descent with modification”  Important points about Evolution through Natural Selection. Natural selection occurs through interactions between individual organisms and their environment, but individuals do not evolve. – A population is the smallest group that can evolve. Evolutionary change is measured as changes in relative proportions of heritable traits in a population over successive generations. Natural selection can act only on heritable traits, traits that are passed from organisms to their offspring. – NS requires genetic variability Environmental factors vary from place to place and from time to time. A trait that is favorable in one environment may be useless or even detrimental in another environment There is no “progress” between species; Nothing in the theory comparing species. Evolution is about differential reproductive success within species Evolution is not about progress towards to a single, ultimate goal. Higher / lower – not what Darwin said Terms like “higher” and “lower” stem from the idea of a great chain of being (or scala naturae) originating all the way back with Aristotle. This was later integrated with European religious beliefs printed The idea of any organism being “higher” or “lower” in 1305 than another should have disappeared after Darwin published his theory of evolution. Darwin himself wrote: o “It is absurd to talk of one animal being higher than another.” o “never say higher or lower in describing the structure of organisms – for if an amoeba is as well adapted to its environment as we are to ours, who is to say that we are higher creatures.” Evolutionary biology does not support the concept of higher and lower. We should recognise that all living organisms are just as evolved as any other but through different selection pressures.  Evolution supported by an overwhelming amount of scientific evidence Evidence for Natural Selection: a) Direct Observation of Evolutionary Change - Examples of Natural Selection b) Homology (anatomy, development and molecular) c) Convergent evolution (Analogous features) d) Fossil evidence e) Biogeography f) Compromises/Bad design  a) Natural Selection in action example 1: Peppered Moth The moths live on the trunks of birch trees (trunk is white). PRE-INDUSTRIAL REVOLUTION, the birds ate the moths they could easily see: the black moths against the white birch bark. –With succeeding generations, the Two variants: proportion of white moths increased. - white with black spots - black with white spots INDUSTRIAL REVOLUTION darkened the white birch due to the soot. Now the white moths were more easily seen. So, birds ate a greater proportion of white moths and with succeeding generations the proportion of black moths increased  a) Natural Selection in action example 2: Antibiotic Resistance The use of drugs selects for pathogens that, through chance mutations are resistant to the drugs’ effects (antibiotic resistant bacteria and drug resistant HIV). : https://www.youtube.com/watch?v=plVk4NVIUh8  b) Homology: Homologous structures Homology: similarity resulting from common ancestry Homologous structures between organisms are anatomical resemblances that represent variations on a structural theme that was present in a common ancestor, but structures serve different functions Ex. Human arm, cat forelimb, whale front flipper, bat wing – strikingly similar arrangements of bones, muscles and nerves DIVERGENT EVOLUTION: is the process whereby groups from the same common ancestor evolve and accumulate differences, resulting in the formation of new species. Divergent evolution may occur as a response to changes in abiotic factors, such as a change in environmental conditions. Alternatively, divergent evolution may take place in response to changes in biotic factors, such as increased or decreased pressure from competition or predation. (ex. beaks of different finches described by Darwin)  b) Homologies: molecular homologies All life forms use essentially the same genetic code (DNA) – Humans & bacteria shares genes! Molecular homologies can also be seen at the level of the finished protein product encoded by the DNA, as shown in this comparison of amino acid sequence in hemoglobin (the protein in your red blood cells that carries the oxygen) of different species...  B) Homologies Vestigial Structures / Organs Vestigial structures are seemingly useless organs or are structures that no longer performs the function for which it evolved Vestigial structures indicate that the organism evolved from ancestors in which the organ was functional Ex. vestigial hind limb bones seen in large snakes and whales indicate that they both evolved from tetrapod ancestors Vestigial eyes are common in burrowing and cave dwelling animals. Ex: Blind mole rat – spends entire life underground  c) Convergent Evolution & Analogous structures When characters are similar, but are NOT derived from a common ancestor = Analogous Bird and insect Analogous structures wing demonstrate that organisms with separate ancestors may ADAPT in similar ways to similar environmental demands CONVERGENT EVOLUTION: Independent evolution of similar structures in distantly related organisms - similar environments → evolved similar Some similar mammals that structures (longs sharp claws & elongated have adapted to similar snouts)→ have evolved independently from environments different ancestors  d) Fossil Record The succession of forms observed in the fossil record – Is consistent with other inferences about the major branches of descent in the tree of life Fossils can document important transitions For example, the transition from land to sea in the ancestors of cetaceans (mammals adapted to aquatic life) ex: considerable evidence suggests that prokaryotes are the ancestors of all life and should precede all eukaryotes in the fossil record. In fact, the oldest known fossils are whale evolution prokaryotes. (vestigial pelvis)  e) Biogeography Species tend to be more closely related to other species from the same area than to other species that live in different areas →suggests a common ancestor adapts to various habitats Earth’s continents were formerly united in a single large continent called Pangaea, but have since separated by continental drift An understanding of continent movement and modern distribution of species allows us to predict when and where different groups evolved resulted in populations becoming isolated in different environments, → evolved differently. Examples from Darwin: (i) Cape Verde island (off W. Africa): plants Ex. Australia's marsupials; an example of and animals resembled those in Africa a diverse group of animals developing in (ii) Galapagos (west Ecuador): plants and isolation. (Australia: separate land mass animals resembled those in S. America -This suggested that the living species on the for millions of years) islands were living descendants from ancestors that had been isolated from the closest mainland.  f) Compromises/Bad Design Vas Deferens: routes sperm from the testicles to the base of the penis in anticipation of ejaculation in humans. Although the direct route is only a few inches, the vas deferens loops up and over the tubes connecting the kidneys to the bladder and back down again because our ancestors' testes were on the inside. Human male embryos start out with their testes on the inside, but they descend to the scrotum during development. Also, it would be better if testes formed outside body. Tested begin development in abdomen and must migrate down into scrotum thru inguinal canals (away from damaging heat from body). The canals leave weak spots in the body that make men prone to hernias. Laryngeal Nerve (branches from vagus nerve): helps us speak and swallow – curious thing is it is MUCH longer than it needs to be. Rather than taking a direct route from brain to larynx, the nerve runs down into our chest, loops around the aorta then travels back to connect to the larynx! watch : https://www.youtube.com/watch?v=sOiH Lcs_L3Q  Why Natural Selection Cannot Fashion Perfect Organisms 1. Selection can act only on existing variations (new advantageous alleles do not arise on demand) 2. Evolution is limited by historical constraints (as we saw in pervious slide) 3. Adaptations are often compromises Frog: Loud call to attract mate Call also attracts predators! 4. Chance, natural selection, and the environment interact  Learning Objectives Understand Natural Selection, understand the 4 steps in the mechanism Understand all the background information Darwin used to develop his idea (Fossil record, knowledge of geography (Hutton & Lyell), artificial selection, Malthus essay of population growth). What did he learn form the data he collected? How did it help him solidify the process of Natural selection? Who is Wallace? Understand why natural selection cannot make perfect species Be able to list and describe scientific evidence to support the theory of Natural selection (Direct Observation of Evolutionary Change/ Examples of Natural Selection; Homology; Convergent evolution (Analogous features); more Fossils evidence; Biogeography, Bad design) Evolution in 6 minutes: https://www.ted.com/talks/prosanta_chakrabarty_four_billion_years_of_evolution_in_six_ minutes?language=en Longer video on laryngeal nerve: https://www.youtube.com/watch?v=cO1a1Ek-HD0 review Natural Selection the MECHANISM that drives evolution Sexual reproduction Struggle for survival – Survival of the results in genetic in the natural fittest – individuals variation / individuals environment living with favorable traits, have slightly different organisms face many survive & reproduce characteristics problems e.g. competition, predation, climatic conditions... review Homologous vs Analogous Homologous features share common ancestry, Analogous features share similar BUT NOT common function functions, BUT NOT common ancestry review More examples of Homologies Vestigial Structures / Organs Goosebumps: These bumps on our bare skin occur in cold weather or when experiencing fear. In our ancestors they would cause the fur to rise up, increasing insulation against the cold and increasing the appearance of size against threats. Wings – no longer used for flying Wings → flippers (but have same bones that we see in the wings of species that can fly) Balance, threat display, mating, shade chicks from sun review Evolution is not goal directed but is reactive This Not this The process of evolution does not work toward an endpoint and does not give an organism what it needs Rather, natural selection acts on already existing structures to create adaptations to their environment (e.g. flaps of skin in flying squirrels) review Difference between Lamarck & Darwin The difference is that Lamarck believed that the changes an organism experienced during its life could be passed on. So, for instance if a giraffe stretched its neck its entire life, it would have longer-necked children. Darwin believed that these traits were immutable, that some giraffes just naturally had longer necks, and these were the ones who had more children. So over time the short-necked giraffes died out and were replaced. review another example of Natural Selection in response to introduced plant species Soapberry bugs use their “beak” to feed on seeds within fruits S. Florida soapberry bugs feed on a vine with larger fruit; they have longer beaks Central Florida they feed on a tree with smaller fruit; they have shorter beaks Natural Selection: Beak length matches depth at which the seeds are found in fruit correlation between fruit size and beak size has also been observed in Louisiana, Oklahoma, and Australia FIG 22.13