Lines of Evidence for Common Ancestry

1. Lines of Evidence for Common Ancestry

2. Evidence of Common Ancestry Fossils Homologies Biogeography Pace of Evolution Chronology in Fossil Record Transitional Forms Anatomical Molecular Cellular Develop-mental Vestigial Structures Plate Tec-tonics Distribution of Living Things Gradual Punctuated Genetic Endo-symbiosis Embryo-logical

3. The Fossil Record • The fossil record provides evidence about the history of life on Earth • It shows how different groups of organisms have changed over time

4. The Fossil Record • Fossils can provide evidence for evolution by dating the rocks in which they were found • The fossils from different time periods can be compared and the changes in the organism’s form noted

5. The Fossil Record • What are some possible causes of stasis (no change in fossils), gradual change, sequential nature of the layer, and sudden appearance and disappearance of fossils • Natural selection happens over many generations, extinction, there are some layers missing from erosion, etc. 

6. Relative Dating • The age of the fossil is determined by comparing its placement with that of fossils in other layers of rock

7. Numerical Dating • Scientists calculate the age of a sample based on the amount of remaining radioactive isotopes it contains

9. Transitional Forms • Fossils or organisms that show the intermediate states between an ancestral form and that of its descendants are referred to as transitional forms

11. Miller and Urey • Stanley Miller and Harold Urey experiments suggest how mixtures of the organic compounds necessary for life could have arisen from simpler compounds present on a primitive earth • Miller and Urey used a mixture of nitrogen, hydrogen, methane, and ammonia in their experiments because this mixture of gases resembles Earth’s early atmosphere

12. Miller and Urey • Miller and Urey produced amino acids by passing sparks through a mixture of hydrogen, methane, ammonia, and water • This suggested how simple compounds found on the early earth could have combined to form organic compounds needed for life

14. Gradualism • Slow and steady nature of biological change • In many cases, the fossil record confirms that populations of organisms did change gradually over time

15. Punctuated Equilibrium • Pattern of long, stable periods interrupted by brief periods of more rapid change

16. Homologies • Organisms that have features homologous to the features of other living organisms, as well as to fossils, provide evidence that organisms living today are linked to each other through common ancestors

17. Homologies • Similar characteristics due to relatedness are known as homologies • Homologous structures derived from a common ancestral form

18. Homologies • There are five types of homologies that provide evidence of common ancestry • Anatomical • Molecular (genetic) • Cellular • Developmental (embryological) • Vestigial structures

19. Homologies • Hoatzin chicks have claws on their wings, as do some chickens and ostriches • This reflects the fact that bird ancestors had clawed hands

20. Homologies

21. Anatomical Homologies • Organisms that are closely related to one another share many anatomical similarities

22. There are four methods scientist use to study homologies and/or similarities in genetics • Compare protein similarities • DNA hybridization • Sequencing DNA • Comparing epigenetics of species: looking at which genes are turned on and off in organisms

23. Genetic Similarities • One way that researchers assess protein similarities is by harnessing the immune system’s ability to recognize foreign proteins • For example, the immune system of a rabbit will recognize a human protein as foreign and will mount an attack against it by making antibodies specific to that protein. • The more similar the proteins from the two species (human and chimpanzee) are, the stronger this second attack will be

24. Genetic Similarities • Research revealed the remarkable similarity between the proteins of humans and those of other great apes • Fewer protein differences corresponded to shorter times of separation • Researchers estimated that humans, chimpanzees, and gorillas shared a common ancestor only 5 million years ago—a much shorter length of time than was commonly accepted at the time.

25. DNA Hybridization • Each DNA molecule is made of two strands of nucleotides • If the strands are heated, they will separate—and as they cool, the attraction of the nucleotides will make them bond back together again • To compare different species, scientists cut the DNA of the species into small segments, separate the strands, and mix the DNA together

26. DNA Hybridization • When the two species’ DNA bonds together, the match between the two strands will not be perfect since there are genetic differences between the species • The more imperfect the match, the weaker the bond between the two strands • These weak bonds can be broken with just a little heat, while closer matches require more heat to separate the strands again.

27. DNA Hybridization • DNA hybridization can measure how similar the DNA of different species is—more similar DNA hybrids “melt” at higher temperatures • When this technique was applied to primate relationships, it suggested that humans and chimpanzees carried DNA more similar to one another’s than to orangutans’ or gorillas’ DNA.

29. DNA Sequencing • DNA sequencing provides evidence of evolutionary relationships • Scientists compare DNA sequences of different species to determine similarities and difference in their genomes. Similarities indicate common ancestry

30. Homologies at the Cellular Level • All living things are fundamentally alike • At the cellular and molecular level living things are remarkably similar • These fundamental similarities are most easily explained by evolutionary theory: life shares a common ancestor • All organisms are made of cells, which consist of membranes filled with water containing genetic material, proteins, lipids, carbohydrates, salts, and other substances

32. Endosymbiosis • The eukaryotic cell possibly evolved from prokaryotic organisms engulfing (through endocytosis) other prokaryotes that had specialized functions such as converting solar energy to sugar (chloroplast) and converting sugars to forms of energy (mitochondria) that could be used by the cell.

33. Endosymbiosis

34. Developmental Homologies

35. Developmental Homologies • Vertebrate embryos in early development are very similar • Early human embryos have structures like gills; also have a tail

36. Developmental Homologies • Some species of living snakes have hind limb-buds as early embryos but rapidly lose the buds and develop into legless adults • The study of developmental stages of snakes, combined with fossil evidence of snakes with hind limbs, supports the hypothesis that snakes evolved from a limbed ancestor

37. Vestigial Organ • Vestigial organs are structures that have apparently lost most or all of their ancestral function in a given species • As the function of the trait is no longer beneficial for survival, the likelihood that future offspring will inherit the "normal" form of it decreases

39. Biogeography • Biogeographyis the study of how species are scattered across the planet and how this happened • Only in the 1960s, as scientists carefully mapped the ocean floor, were they able to demonstrate the mechanism that made continental drift possible—plate tectonics.

40. Biogeography • Russel Wallace, a naturalist, began his travels in 1848 through the Amazon and Southeast Asia • On his journeys, he sought to demonstrate that evolution did indeed take place, by showing how geography affected the ranges of species

41. Biogeography • In 1915 the German geologist Alfred Wegener was struck by the fact that identical fossil plants and animals had been discovered on opposite sides of the Atlantic • Since the ocean was too far for them to have traversed on their own, Wegener proposed that the continents had once been connected • Wegener found that the distributions of fossils of several organisms supported his theory that the continents were once joined together.