Evolution

1. Evolution • Definition: A process of change in species through time which is based on genetic variation

2. Example: Modern elephant is a result of a changes in ancestors over millions of years Many ancestors have died but their DNA or genes are part of organisms that live today.

3. Another way to represent this change over time is through a tree diagram. The closer the branches the more alike the species.

4. Elephants are just one branch of many on the evolutionary tree.

5. The tree is a way of showing genetic relationships between species: Species that break off a common branch are more similar than those that break off from different branches.

6. Humans are only one twig on a very full tree. Because a species is at the end of a branch that does not mean they are superior in terms of evolution. It simply means that they descended from and genetically related to those that came before. • Tips for reading evolutionary trees. • If a branch ends that means the species or group died off without producing a modern species. • If a branch continues on to the edge that means the group is current.

7. I. Evidence of Evolution • Evidence that supports the theory comes from many different sources including: -fossils from the geological record - cytology (cell study) -biochemistry -embryology -anatomy

8. Geological record • Geologist estimate the earth is 5 billion years old • In strata (undistributed layers) of sedimentary rock, it is possible to find fossils in upper strata that resemble (different species) those in lower strata. Leads to theory that genetic links b/w modern life and ancient life.

9. Law of Superposition – Rock layers on bottom are OLDER than rock layers on top

10. What is a fossil? Fossils = any trace of or remain of an organism preserved by natural processes -types of fossils: amber, ice, bones, petrifacation, molds, casts, & imprints.

11. B. Comparative Cytology • Cytology - Study of cells • All living things are made of cells • Plant and animal cells are quite similar suggesting a common ancestor. • List some differences b/w plant and animal cells - plants have cell wall, animal cells don’t -plant cells have chloroplasts -animal cells have centrioles.

12. Comparative Biochemistry • DNA & protein structure is similar in closely related species Examples: insulin & thyroxin from a pig, cow & sheep can be used to treat humans. Remember DNA is the instructions for making proteins and chemicals. The same protein means the same DNA.

13. D. Comparative Embryology 1. Reproductive process is similar in different organisms. 2. The existence of the amnion in the egg of a bird & the uterus of a mammal

14. Embryos of most vertebrates show a great deal of similarity in early stage of development Human Pig Chick

15. Analogous structures – structures found in different types of organisms that are similar in function or outward appearance, but dissimilar in basic structure or development. Ex: wing of butterfly and wing of bird. Remember the word Analogy – Similar in one way but not in any other. (Feather is to Bird as Hair is to Mammal) EXPLORATORIUM

16. E. Comparative Anatomy • Similar organisms can be shown to have limbs, internal organs, or other structures that are constructed similarly. • Called homologous structures. • Believed to have originated from common ancestral forms of the same organ (THIS DOES NOT NECESSARLY MEAN THAT THEY FUNCTION THE SAME WAY)

18. Vestigial Organs

19. Some organisms have structures or organs that seem to serve no useful function. -Ex humans have a tailbone at the end of the spine, snakes w/ tiny pelvic bones and limb bones • Functionless parts are called vestigial organs or structures. • Vestigial organs are often homologous to organs that are useful in other species. The vestigial tailbone in humans is homologous to the functional tail of other primates

20. II. Heterotroph Hypothesis- Origin of Life • 5 billion years ago the earth was comprised of water (H20), ammonia (NH3), methane (CH4), Hydrogen (H2) • There was also sun’s X-rays & UV radiation which was unfiltered, lightening & volcanic activity

22. The hypothesis states these components synthesized simple biochemical molecules (ex: simple sugars, amino acids, & lipids) • These substances formed longer “chain” molecules of polypeptides, polysaccharides, & hydrocarbons 1. These same chains FLUID MOSAIC MODEL of the cell membrane

23. Stanely Miller -set up an experiment that supports the idea of the heterotroph hypothesis. His experiment: flipped a switch sending electric current through a chamber containing a combination of methane, ammonia, hydrogen and water. This yielded organic compounds including amino acids, the building blocks of life. Called primordial soup

24. III. Modern Theory of Evolution • How did humans evolve? • Early theories 1. Jean Baptiste de Lamarck (1809) – thought that evolutionary changes in animals were caused by their need to adapt to changes in the environment.

25. His theory involved 2 principles: • The Law of Use & Disuse – assumed the more a body part is used, the stronger & better it becomes; opposite for body parts that are not frequently used. • Inheritance of acquired characteristics – assumed that the characteristics an organism developed thru use & disuse could be passed to offspring. This theory later proved to be incorrect

26. 2. August Weismann (1870’s) • Weismann best proved that genes are not affected by an individual’s life experiences or activities. • How? He cut tails of mice for 22 generations and saw that shortened tails were NOT inherited.

27. IV. Modern Theory • Based partially on Darwin’s concept of natural selection. A. Charles Darwin (1830’s) made several observations; the most significant were on the Galopagos Islands where he developed his theory of evolution.

28. B. Darwin’s Theory of Natural Selection – organisms with favorable variations would be better able to survive & reproduce than organisms with less favorable variations. -The unequal survival and reproduction of organisms due to environmental forces -“Nature” selects

29. Parts of Natural Selection 1. Overproduction -All populations tend to overproduce but… - Populations increase geometrically (2->4->8->) but there is mortality before reproduction -Survival to reproduce –    “Survival of the fittest” –    “ Reproduction of the fittest”

30. 2. Competition – living space & food are limited. Organisms have to compete with their own species and others for the resources. 3. Variation – differences that exist within a species; such as shape, strength, resistance to disease & others. Some are beneficial.

31. Adaptations – because of the variations, some organisms are better adapted to survive & reproduce which would then perhaps pass on that trait to improve that individuals offspring’s chance for survival. Example: Darwin’s Finches

32. Speciation – formation of a new species; one of the most important factors involved in speciation is isolation. a. Geographic isolation – occurs when a population is divided by a natural barrier (mtn, river, desert or ocean)

33. C. Examples of Natural Selection • Industrial melanism – Prior to 1800, the peppered moth had a light pattern, dark colored or melanic moths were rare -During the Industrial Revolution, soot darkened tree trunks and killed off lichens. The light-colored morph of the moth became rare and the dark morph became abundant - The dark coloration was now favored b/c it camouflaged the moths from predation by birds.

34. The Darwin's Finches diagram below illustrates the way the finch has adapted to take advantage of different ecological niche's. • Their beaks have evolved over time to be best suited to their function.

36. D. Problems with Darwin’s Theory • It doesn’t explain how variations originate • It doesn’t distinguish between variations caused by hereditary differences & variations caused by the environment, which are not inherited.

37. V. Rates of Evolution • Today scientists are not sure on a rate of evolution or species formation • Some past theories include… A. Gradualism – according to Darwin, evolution occurs slowly & continuously over millions of years.

38. B. Punctuated Equilibrium – according to Steven J. Gould & Niles Eldredge (newer theory) species remaining in constant or equilibrium over a long period of time and then the equilibrium is interrupted or punctuated by a short period of rapid evolution.

39. Fossil record supports this idea (trilobite, brachiopod and some dinosaurs) Archaeopteryx was often cited as an example of an intermediate form between "reptile" and "bird."

40. 2. extinctions

41. VI. The Synthetic Theory of Evolution • Modern biologist have combined Darwin’s basic theory with the findings of genetics & population biology to form this theory which states that evolution is happening to populations NOT individuals. • "EVOLUTION IS NOW DEFINED AS A CHANGE IN THE ALLELE FREQUENCY WITHIN A POPULATION OVER TIME."

42. Population – a group of organisms of the same species living together in a given region that are capable of interbreeding. 1. Gene frequency – in a population, there are a certain # of alleles of each kind. All individuals may have a copy = 100% frequency. Mutations sometimes occur & the gene frequency will account for this.

43. Gene Pool – total of all alleles present in a population. • Evolution is the gradual change of the allele frequencies in a population C. Hardy-Weinberg Law – the principle that sexual reproduction alone does not affect allele frequencies in a population.

44. VII. Speciation • Species definition - a group of populations through which genes can flow and whose offspring have a fitness equal to the parents • Speciation - formation of two or more different  species from one original population

45. -Evolution does not necessarily mean long term progress is going to go in a certain direction.   -Evolutionary changes often appear to be like the growth of a bush: Some branches survive from the beginning with little or no change, many die out altogether, and others branch out repeatedly, sometimes giving rise to more complex organisms.

46. Note the divergence of the various groups from a common ancestor and the fact that some branches became extinct.

47. Extinction of a species occurs when the environment changes and the adaptive characteristics of a species are insufficient to allow its survival. • Fossils indicate that many organisms that lived long ago are extinct.   • Extinction of a species is common; most of the species that have lived on earth no longer exist.

48. Small differences between parents and offspring can accumulate in successive generations so that descendants become very different from their ancestors. • The degree of kinship between organisms or species can be estimated from the similarity of their DNA sequences; this similarity often closely matches organisms' or species' classification based on anatomical similarities.

49. Classification • Importance: help group living things in an organized way to make them easier to study. • Taxonomy = the science of naming and classifying organisms • Basis – classified based on similarity in structure (external, internal, or cellular)

50. II. Classification Groups • Developed by Carolus Linnaeus • Organisms are separated into smaller and smaller subgroups based on common characteristics. • Largest group to smallest • Kingdom, Phylum, Class, Order, Family, Genus, Species