University:
California State University, Northridge
Course:
BIOL 322 | Evolutionary Biology
Academic year:

2006
Views:

41

Pages:

44
Author:

Bunicco14j

Some Evidence of Evolution Pre-Darwin western Christian thought • Life arose by special creation • Organisms were formed as we find them today – That is species do not change • Believed to be recent – In 1664 Archbishop James Ushher calculated that the earth was 5668 years old – 26th of October, 4004 B.C., 9 AM Facts and Inferences • Facts are observable things • Inferences are extensions to what is not directly observed Claims of special creation • Species created independently • Species do not change through time • Created recently • Process inferred from those claims is that some God did it Claims of Darwin • Species change through time • Species related to each other as ancestordescendant • Life on earth is ancient • Process inferred: ‘descent with modification’ • Process of adaptation: ‘natural selection’ Any evidence? • Are species independent? • Are they unchanging? • Is life recent? Are species independent, or do they show shared ancestry? • Shared ancestry proposed before Darwin – Comte de Buffon, Erasmus Darwin, JeanBaptiste Lamarck – What Darwin provided was the mechanism of adaptive evolutionary change • Natural selection • Comparative anatomy was basis Homology and Analogy • Homology (modern sense): similar by descent or ancestry • Analogy: similar not by descent – In conversation: ‘let me compare thee to a summers day’ – In biology: similar selection pressures produce similar adaptations • E.g. desert plants in N. America share many water saving features with other desert plants Vertebrate forelimbs Making sense of similarity • If you built a flying limb from scratch, you would design it differently than you would design a swimming or grasping or running limb • The similarity of structure despite very different function suggests similarity of origin • Called structural homology Other homology examples • Embryology – Louis Agassiz (among others) showed that vertebrate embryos in early development are very similar – Early human embryos have structures like gills; also have a tail • Called Developmental Homology Human embryo with tail Genetic Homology • Structural homologies are similar because they share developmental homology • Developmental homology is the result of genetic homology ‘Universal’ genetic code Genetic homology in homeodomain eye genes Thought question • Biomedical researchers often seek treatments for human disease by doing experiment in other species (e.g. mice) • How successful would they be if mice and humans did not share numerous homologies? All this homology suggests shared ancestry • Shared ancestry….what does that mean? • Often said that “humans evolved from apes” • People think that means that modern humans descended from modern apes • Thoughts? Phylogenetic tree: tips, branches, nodes Parsimony • Important principle of science • Simply explanations are favored over complicated ones (Ockham’s razor) • In general English usage: less, or sparing • In biology usage: requiring less evolutionary change So a horse, a zebra and a chicken go into a bar…….. • Which is more parsimonious? • The horse and the zebra are more closely related than either is to the chicken, or • The chicken and the horse are more closely related than either is to the zebra Do species change over time? • Evidence from living species – Vestigial traits – Direct observation – Fossil record • Evidence from fossils – Extinction – Transitional forms – Environmental change Vestigial structures • Vestigial structure: functionless or rudimentary homolog of a structure that has an important function in closely related species Examples of vestigial traits Also: Your appendix Wisdom teeth Goose bumps Vestigial traits can be: • Structural – Tail bone in adult humans • Developmental – Embryonic tail Does it make sense to have a tail bone and an embryonic tail UNLESS your ancestors had tails? Vestigial Genes • Genetic – Pseudogenes: nearly normal genes that are not transcribed to protein – E.g., psi-alpha locus of hemoglobin – Resembles that alpha locus but has a mutation that stops transcription Direct observation of change over time • Change from AZT susceptible to AZT resistant HIV strains repeatedly found within patients? • 100’s of other examples, finch beaks being the most famous • Soapberry bugs another good one Soapberry bug beak length evolution What about fossils? Fossils provide three types of evidence for evolution • Evidence of extinction • Evidence of change of species through time • Evidence of age of life Extinction • Was actually controversial in early 1800’s • By 1812 Cuvier published Irish Elk analysis But how does the fact of extinction help the case for evolution? • Species do not persist indefinitely; that suggests life on earth changes •Fossils prove that life isn’t set in stone Change through time: Transitional fossils • Fossils species intermediate between modern living forms • Fossil species intermediate between older and younger fossils, or older fossils and modern forms Ambulocetus natans, ca. 50 mya, described 1994, from Pakistan Basilosaurus isis, ca. 38 mya, described 1990, from Egypt Modern baleen whale Whale fossils from Egypt and Pakistan? • Marine fossils found high and dry – Clearly, the earth changes – But does it change fast or slow? • Before the late 1700’s, change thought to be rapid, e.g. Biblical floods, other ‘catastrophies’ – Catastrophism: hypothesis of catastrophic rapid change Geological Evidence • James Hutton and Charles Lyell • British geologists, actually set out to measure rates of geologic change (wow, science!) • Determined that the rates of geologic change are very very slow Why is that important? • If rates of change are very very slow (which mostly they are) • AND • If the rates of change in the past were similar to the rates observed today – Why would they be different? • Then the earth must be very old, much much older than Archbishop James Ussher’s 6000 years. How Old? Current estimate’s Earth ~4.6 bya Life ~3.7 bya How do you know that? • Relative age dating techniques – – – – Deeper layers are older Layers are originally flat Rocks within other rocks are older But rocks that fill cracks in other rocks are younger • Those are good, but you’d like actual ages Actual ages: Radiometric dating • Isotopes decay at characteristic rates, called halflives • A half-life is the amount of time it takes for 1/2 of the isotope to decay Summary of Facts • Species are not independent – Homology: structural, developmental, genetic • Species change – Observable in populations today – Observable through time in fossils • Life on earth is ancient – Earth 4.6 Billion years; Life 3.7 Billion years So not special creation, then how? • Process inferred: – ‘descent with modification’ • Process of adaptation: – ‘natural selection’ • Natural selection next lecture

Some Evidence of Evolution

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