Evolution

1. Evolution

2. What is Evolution? • Although all living creatures share a common ancestry, they have come to differ from each other through the process of evolution.

3. Biological evolution refers to genetic change over successive generations • Process of change is characterized by decent with modifications, as descendant populations diverge from ancestral ones

4. As population’s genetic variation changes from one generation to another, genetic change is reflected in visible differences between organisms. • With significant genetic change, a new species can appear

5. The process of evolution provides a mechanism to account for the diversity of life on earth

6. What is the Molecular Basis of Evolution? • With discovery of DNA molecules in 1953, scientists came to understand how genetic information is stored in the chromosomes of a cell

7. Genes • Genes, specific portions of DNA molecules, direct the synthesis of the protein molecules upon which all living organisms depend

8. Through process of biological reproduction, each of us inherits a combination of genes from our biological parents that creates a unique new individual

9. What are the forces responsible for Evolution? • Mutation • Genetic Drift • Gene Flow • Natural Selection • These account for change in the genetic compositions of populations

10. Mutation • Ultimate source of evolutionary change • Introduces new variations…some are harmful or helpful…most are neutral • Evolutionarily, it is positive because new variations are created.

11. Mutation • New body plans (such as bipedalism compared to knuckle walking) ultimately depends on mutation • Without variations brought in through mutation, populations would be unable to change over time as a response to environmental changes • Mutation don’t have to physical changes

12. Mutation • Activity: • If you could create a mutation, what would it be and why? • What mutation(s) in your opinion would be beneficial to humans right now? Think of what we do, where we do it, how we do it, and is there a better way to do it?

13. Mutation • For sexually reproductive species (humans) the only way mutations of any evolutionary consequences are those occurring in sex cells, since these cells form future generations

14. Mutations • Mutations arise when mistakes in copying DNA have occurred. • Luckily, we have a built in system that usually erases the mistakes (but some are missed…obviously) • Environmental factors may increase mutations

15. Mutation • Mutations ensure versatility at population level, making it possible for an evolving species to adapt more quickly to environmental change • Remember: mutations occur randomly and thus do not arise out of need for new adaptation.

16. Genetic Drift • Chance fluctuations of allele frequencies in the gen pool of a population • Allele: any of several forms of a gene, usually arising through mutation, that are responsible for hereditary variation.

17. Genetic Drift • These changes at population level come about from random events at the individual level. • Over the course of lifetime, individuals are subject to a number of random events that affect its survival

18. Genetic Drift • Ex’s: • Healthy squirrel with advantageous traits may be killed in a forest fire • Genetically well adapted baby cougars may not survive as their mother was killed in an avalanche, while weaker ones survived because their parent survived.

19. Genetic Drift • In a large population, accidents are unimportant • Accidents that preserve individuals with certain alleles will be balanced out by the accidents that destroy them • **Except for smaller populations (alleles may be overrepresented)

20. Genetic Drift • Human population is considered large (7 Billion), so we may assume that Genetic Drift doesn’t occur • Ex: a chance event that kills 5 people in an isolated population (island) may affect the gene pool of entire population (1000 people)

22. Pingelap Example • Tiny island in South Pacific where 5% of entire population is completely colour blind (not the variety that affects 8-20% of most populations) • Typhoon swept the island killing all but 20 individuals • 1 had this condition… and after generations…. • 30% of island has condition compared to 0.003%in USA

23. Genetic Drift • Likely important in human evolution because up until about 10,00 years ago, humans were foragers living in small groups (so geographically isolated in a sense) • When biological variation is observed – always possible that genetic drift is responsible (think of how humans branched out…)

24. Gene Flow • Introduction of new alleles from nearby groups • Interbreeding allows “road tested” genes to flow into and out of populations • Migration may lead to gene flow

25. Gene Flow • 2 factors that can affect Gene Flow: • Geographic factors • Social factors

26. Geographic factors • Ex: populations separated by river preventing interbreeding • Pops begin to accrue random genetic differences due to geographic isolation • If river ever changes course (and it will), both populations can breed freely, and new alleles present in only 1 population will now be present in both due to gene flow

27. Social Factors • Mating rules • Intergroup conflicts • Ability to travel great distances today (migration, globalization) • Ex: last 500 years of colonialism and slavery affecting populations of Cent/South America • This introduced alleles from Spanish and African populations to the Americas (appearance of some in South America)

29. Gene Flow • Throughout history of life on earth, gene flow has kept human populations from developing into separate species

30. Natural Selection • Although Genetic Drift and Gene Flow produce change in alleles, change does not necessarily make population better adapted to it’s biological and social environments • Natural Selection, accounts for adaptive change (as Darwin suggested)

31. Adaptation • Series of beneficial adjustments to the environment. • Adaptation is not the active process but the outcomes of Natural Selection

32. Natural Selection • Humans can adapt through culture as well as biology • When biological adaptations occur at the genetic level – Nat. Selection at work

33. Natural Selection • Shaped to fit local environmental conditions • Instead of random selection whose traits will be passed on to the next generation, there is a selection by forces of nature • As a consequence of the process of Nat. Selection, populations generally become well adapted to their environment

34. Trees! • Cacti • Coniferous tree • Broad leaf trees

38. Other Orgs

40. Neat Facts • Some desert animals secrete crystals to prevent de-hydration (instead of peeing) • Most animals in hot places would be nocturnal • 6 coolest adaptations

41. Natural Selection • The way it works: • Frequency of genetic variants for harmful OR non-adaptive traits within the population is reduced, WHILE frequency of genetic variants for adaptive traits are increased

42. Natural Selection • Survival of the Fittest? • Physically weak or unfit are eliminated through starvation, disease, or predation • Some bearing on Nat Selection

43. Natural Selection • Cases of “less fit” doing quite well • First; what is “doing well” as a species?

44. Uganda Kob • Antelope males unable to attract mates form a “bachelor herd” and therefore have safety in numbers to protect themselves and live long lives on average

45. Other example

47. Natural Selection • Measured in terms of reproduction success Reproduction success: mating and production of viable offspring who will carry on one’s genes. ***Also a powerful social phenomena in some cultures where women’s social worth is assessed in terms of her ability to bear children (article)

48. Natural Selection • Nat. Selection may also promote stability rather than change. • Stabilizing Selection: occurs in populations that are well adapted or where change may be detrimental

49. Natural Selection • It is true that all organisms have many adaptive characteristics • It is not true that all characteristics are adaptive • Ex: Nipples on males.

50. Ex: Nipples on male mammals • To female mammals, nipples are essential for reproductive success, which is why males have them. • Two sexes are separate entities to natural selection, but are variants upon a single body plan, elaborated later in embryology