1. Bio Crash Course Evolution

2. Darwin Charles Robert Darwin – English naturalist and geologist, best known for his contributions to evolutionary theorynaturalistgeologist – Travelled on the HMS Beagle 1831-1836, to the Galapagos Island and observed species that lead to his theory of evolution – On the Origin of Species was a joint publication with Alfred Russel Wallace Alfred Russel Wallace

3. The Theory – Darwin's Theory of Evolution is the widely held notion that all life is related and has descended from a common ancestor – descent with modification: complex creatures evolve from more simplistic ancestors naturally over time. – random genetic mutations occur within an organism's genetic code, the beneficial mutations are preserved because they aid survival -- a process known as "natural selection." – These beneficial mutations are passed on to the next generation. – Over time, beneficial mutations accumulate and the result is an entirely different organism (not just a variation of the original, but an entirely different creature).

4. The Theory – Natural selection acts to preserve and accumulate minor advantageous genetic mutations. Suppose a member of a species developed a functional advantage (it grew wings and learned to fly). Its offspring would inherit that advantage and pass it on to their offspring. The inferior (disadvantaged) members of the same species would gradually die out, leaving only the superior (advantaged) members of the species. – Natural selection acts only by taking advantage of slight successive variations; she can never take a great and sudden leap, but must advance by short and sure, though slow steps." "If it could be demonstrated that any complex organ existed, which could not possibly have been formed by numerous, successive, slight modifications

5. 27-5 Evidence of evolution Overview – Evolution encompasses common descent and adaptation Common descent – All organisms are composed of cells – All take chemicals and energy from the environment – All reproduce, respond to stimuli, and evolve – Earth is approximately 4.5 billion years old Prokaryotes arose about 3.5 billion years ago Eukaryotes about 2.1 billion years ago, but multicellularity came much later at 700 million years ago – Most evolutionary events occurred in less than 20% of the history of life!

6. 27-6 Evidence of evolution cont’d. Fossil evidence – Hard body parts are preserved in most cases – Often embedded in sedimentary rock layers represent eras in geological time Each layer is older than the one above and younger than the one below – Transitional fossils Especially significant- represent evolutionary links ex. Tiktalik Geological time scale – History of Earth is divided into eras Based on dating of fossil evidence – Relative dating method-noting which layer a group of fossils comes from – Absolute method-radioactive carbon dating – The geological time scale is shown on the following slide Note the examples of principal plant and animal life during each era

7. 27-7 Evidence of evolution cont’d. Biogeographical evidence – Study of distribution of plants and animals – Earth has 6 biogeographical regions Each has its own distinctive mix of species – Barriers prevented evolving species from migrating to other regions – Continental drift-positions of continents and oceans has shifted through time 225 million years ago continents were one land mass Distribution of fossils and existing species allows us to determine approximate timeline

8. 27-8 Evidence of evolution cont’d. Anatomical evidence – Common descent offers explanation for anatomical similarities Homologous structures- have same function and same basic structure, indicating a common ancestor – Ex: human arm and whale forelimb Analogous structures- same basic function but different origins – Ex: wing of bird and wing of bee Vestigial structures-anatomical structures fully functional in one group and reduced, nonfunctional in another – Humans have a tailbone (coccyx) but no tail – Homology extends to embryonic structure Gill slits, notocord, pharyngeal pouches

9. Convergent and Divergent Divergent Evolution: - When a species diverges over time into two different species, resulting in a species becoming less like the original one - Live in different ways than the common ancestor - Caused by migration or nearby extinction of a nearby environment - Prime example are the dinosaurs Convergent Evolution: - When unrelated organisms evolve similarities when adapting to similar environments - Live in the relatively same way as each other - Emus, rheas, and ostriches are prime examples of convergent evolution

10. 27-10 Bones of the vertebrate forelimb Fig. 27.4

11. 27-11 Evidence of evolution cont’d. Biochemical evidence – All organisms use same basic biochemical molecules DNA ATP Identical or nearly identical enzymes – Many developmental genes are shared – Degree of similarity between DNA base sequences and amino acid sequences indicates the degree of relatedness Evolution is one of the great unifying theories of biology

12. 27-12 27.3 Process of evolution Microevolution- a change in gene frequencies within a population – Population genetics Population- all members of a species occupying a particular area at the same time – Mating is purely random – Genes are passed on according to Mendel’s laws Gene pool- the sum total of all alleles of all genes in a population – Hardy and Weinberg used the binomial equation p 2 +2pq+q 2 to calculate the genotype and allele frequencies in a population – Predicts that gene frequencies will remain constant from generation to generation – This is illustrated in the following slide of Fig. 27.11

13. 27-13 Process of evolution cont’d. The Hardy-Weinberg law – Equilibrium of allele frequencies in a gene pool will remain constant in each generation of a large sexually reproducing population as long as the following 5 conditions are met No mutations occur No genetic drift occurs-random changes in gene frequency No gene flow Mating is random No selection is occurring – In real life these conditions are virtually never met – Hardy-Weinberg law gives us a baseline by which to access whether or not evolution has occurred Any change in allele frequencies indicates evolution

14. 27-14 Process of evolution cont’d. Five agents of evolutionary change – Mutations Only source of new alleles in a population Can be an adaptive variation – Genetic drift Change in allele frequencies due to chance 2 main mechanisms – Founder effect-a few individuals found a colony and their collective genes represent only a fraction of the original gene pool – Bottleneck effect-population is subjected to near extinction by a disaster and so only a few genotypes contribute to next generation

15. 27-15 Process of evolution cont’d. Five agents of evolutionary change cont’d. – Gene flow Movement of alleles between populations Keeps the gene pools of 2 or more populations similar – Nonrandom mating Occurs when individuals pair up according to phenotype or genotype Inbreeding is an example-increases frequency of recessive abnormalities

16. 27-16 Process of evolution cont’d. Five agents of evolutionary change cont’d. – Natural selection Process by which populations adapt to their environment Charles Darwin explained evolution through natural selection Evolution by natural selection requires the following – Variation-members of a population differ – Inheritance-differences are inheritable – Differential adaptedness-some differences have a survival benefit – Differential reproduction-better adapted individuals survive to reproduce more offspring

17. 27-17 Process of evolution cont’d. Natural selection cont’d. – Fitness- measured by the number of fertile offspring produced by an individual Variations that can contribute to fitness can arise from – Mutation – Crossing over – Independent assortment – Most traits on which natural selection acts are controlled by polygenic inheritance – Range of phenotypes which follows a bell-shaped curve

18. 27-18 Speciation cont’d. Process of speciation – Occurs when on species give rise to two species Occurs when reproductive isolation develops – Allopatric speciation- geographical barriers separate a population into 2 groups Premating and then postmating isolating mechanisms occur – Sympatric speciation-occurs without geographical barriers 2 subgroups of a population become reproductively isolated Best illustrated in plants- multiplication of chromosome number in one individual may lead to asexual reproduction and offspring with the same multiple chromosome number- isolates them from others

19. 27-19 Speciation cont’d. Adaptive radiation – A specific type of speciation which gives rise to many new species – Galapagos Islands finches- studied by Darwin Example of adaptive radiation Mainland finches migrated to one of the islands – Reproduced and eventually spread to all the islands – Subjected to different environmental selection pressures Gave rise to many species of finches which differ primarily in beak shape – Adapted to allow use of different food sources

20. 27-20 Cladogram Fig. 27.23