Chapter 19: Change in Species

1. Chapter 19: Change in Species What evidence exists to support evolution?

2. 19.1 Fossil Evidence • Fossils – physical remains of ancient organisms • Fossils = largest piece of evidence for evolution

3. 19.1 Fossil Evidence • Paleontology – the study of fossils How do fossils offer information about change?

4. 19.1 Fossil Evidence How do fossils offer information about change? • They are a record of organisms that are not around today. • Ancestral relationships can be based on where they are found in relation to another fossil.

5. 19.1 Fossil Evidence How do fossils offer information about change? • They can show us the rate of evolutionary change. • They are a clue to the physical structure of living things (clues to behavior).

6. 19.2 Ecology & Homologies • Coevolution – the continuous adaptation of different species to each other • Example: predator-prey relationships Galapagos tortoises & Cacti – the cacti have developed tall woody stems; tortoises have developed flared saddleback shells so their necks can stretch farther

8. 19.2 Ecology & Homologies • Example: Flowers & pollinators Bees have developed characteristics that make pollen stick to them (hairy abdomens) & flowers have developed characteristics to make them attractive to bees & other pollinators (colorful petals, smells)

10. 19.2 Ecology & Homologies • Artificial Selection Works in same way as “natural selection” except that someone controls the characteristics that are being chosen Example: dog breeding

11. 19.2 Ecology & Homologies • Homologies = similarities between species that suggest common ancestry (remember from last chapter) • Homologies help biologists understand the history of evolutionary changes

12. Example: Forelimbs of vertebrates Shows evidence that these organisms have an ancestor in common.

13. Example: Mouse/Fruit fly eyes Put the gene coding for eyes in mice into an eyeless fruit fly chromosome & the fly grew eyes

14. 19.3 Genetic & Molecular Evidence • Darwin’s problem: explaining how variations are inherited • Study of genetics has provided more support for the theory of evolution

15. 19.3 Genetic & Molecular Evidence • Sources of genetic variation: • Mutation • Recombination of alleles – happens in sexually reproducing organisms; includes crossing over & fertilization to produce new combinations of genes

16. 19.3 Genetic & Molecular Evidence • Genetic variation is the RAW MATERIAL OF EVOLUTION!! • We use molecular data (DNA information) to see the degree of relatedness between species – more DNA in common, more closely related.

17. Other Evidence for Evolution • Embryos Early in embryonic development, it is very difficult to tell different organisms apart. The fact that we start off so similarly is evidence we all came from a common ancestor.

18. Other Evidence: Embryos

19. Other Evidence for Evolution • Skulls Used often in human evolution – changes in skull shape/size show changes in humans over time

20. Other Evidence for Evolution • Vestigial Structures • Structures that are no longer useful in an organism (ex: appendix, goosebumps, body hair, etc. in humans) • Shows changes in organisms over time – our distant relatives needed them for something but over time they no longer are needed

21. 19.4 Process of Speciation • Speciation – the appearance of a new species • Examples that have been observed: primarily in bacteria (because they reproduce – and so, evolve – so quickly); new species of grain – crossed wheat and rye

22. 19.4 Process of Speciation • POPULATIONS EVOLVE, NOT INDIVIDUAL ORGANISMS WITHIN A POPULATION!! • Speciation occurs when 2 populations become so different in their genetic makeup, they can no longer interbreed.

23. 19.4 Process of Speciation • Usually occurs as a result of isolation – a small population that gets isolated from the rest of the population develops into its own species.

24. 19.4 Process of Speciation • 3 Types of Isolation: 1. Geographic Isolation: most common; organisms cannot come into contact with one another so they can’t interbreed (get separated by body of water, mountain range, canyon, etc.)

25. 19.4 Process of Speciation • 3 types of isolation: 2. Ecological isolation: When two different populations adapt to different habitats

26. 19.4 Process of Speciation • 3 types of isolation: 3. Reproductive isolation (also behavioral): the mating patterns of a small group of organisms becomes so different from the main group that they become reproductively isolated

27. 19.5 Patterns in Evolution • Adaptive radiation – the development of numerous species from a common ancestor in a diverse environment • When a population enters a habitat with few competing species, it will often divide into many smaller populations by adapting to different environments or using different resources

28. 19.5 Patterns in Evolution • Stasis – the rate of large-scale change remains very slow for a long period of time • Causes of stasis: species is well adapted & the environment remains stable • Example: the Australian lungfish – changed little in millions of years; the horseshoe crab

29. 19.5 Patterns in Evolution • Two ideas on Progress of Evolution: 1. Gradualism – Speciation & evolutionary change occurred through the accumulation of many gradual & constant changes

30. 19.5 Patterns in Evolution • Two ideas on Progress of Evolution: 2. Punctuated Equilibrium – Short period of rapid change just after a population becomes isolated and forms a new species, after which the process slows and approaches stasis

32. Population Genetics (from 16) • Microevolution – changes within species occurring over dozens – hundreds of generations • Changes in the frequencies of alleles in a population • Macroevolution – the larger changes of a species over time usually leading to the formation of new species (what we’ve been dealing with so far)

33. Population Genetics • Hardy-Weinberg model of Gene Pools A mathematical model of gene pools that enables us to use the frequency of alleles in a population to calculate all the genotype frequencies in that population.

34. Population Genetics • Hardy-Weinberg p2 + 2pq + q2 = 1 p + q = 1 p = dominant allele (A) q = recessive allele (a) p2 = homozygous dominant individuals (AA) q2 = homozygous recessive individuals (aa) 2pq = heterozygous individuals (Aa)

35. Population Genetics • Hardy-Weinberg: 5 Conditions 1. Mutation rate is negligible. 2. Migration is negligible. 3. Population is large, diploid, & sexually reproducing. 4. Mating is random. 5. Natural selection does NOT occur.

36. Population Genetics • Hardy-Weinberg: 2 important results 1. It enables you to use the allele frequencies to calculate all of the genotype frequencies. Example: If 50% of the alleles in a population are dominant (A) and 50% of the alleles in a population are recessive (a), what percentage of the population are heterozygous?

37. Population Genetics • Hardy-Weinberg: 2 important results 2. The allele frequencies are stable over time (under the assumptions of the model). This supports the idea that there will be variation in a species.