evolution - | department of zoology at ubcadamson/biol121-122/7.b121.2012evolution1.pdfevolution...
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Evolution
Origins of life Origin of species (diversification of life)
Origins of adaptation
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The reproductive process in biology inevitably produces evolutionary change
• Mutations will occur: p(mutation)>0. • To the extent that populations are separated
from one another, divergence will occur. • i.e., some amount of evolution is an
inevitable result of thermodynamics associated with reproduction.
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Evidence of Evolution Ch 24
• Change through time: – Fossils: extinction, transitions, environmental change
– Comparative studies: vestigial traits – Current studies: drug resistance, etc
• Species are related to one another. – Biogeography
– Homology: structural, developmental, molecular (genetic)
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Fossils
Georges Cuvier (1773–1838)
• First detailed study of fossils.
• Comparative anatomy. • Correlation of parts. • Extinction.
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Fossil dating
Generic dating. Ppres = Porig (2 (-age/halflife)) – Isochronic dating is better in
that it avoids assumption that there was no daughter isotope at t=0, and will signal if new material was added to the site at a later date.
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Fossil Dating
• Radioactive decay and absolute age:
• earth 4.6 by old. Life arose ~3.8 by ago. First Eukaryote fossils ~1.5 by ago.
• Humans diverged from other Apes ~5 my ago. Homo sapiens ~0.5 my ago.
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Extinction
• The Irish elk: actually an extinct deer. Widely distributed in Pleistocene.
• Cuvier 1812 described fossil remains. Evidence of extinction.
• Many examples are now known of extinct creatures preserved as fossils from all eras.
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Transitional forms • Birds and other dinosaurs • Whales and Ungulates
Darwin noted that fossils in an area often resembled organisms living in the area
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Vestigial traits
• Reduced or modified function.
• Even molecular examples: L-gulano-γ-lactone oxidase: gene required to synthesize vitamin C.
• non functional in humans, guinea pigs.
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Environmental Change
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Species are related to other species
• Species fall into groups within groups. Indicates branching evolutionary processes; descent with modification. Doesn’t occur with man-made objects or rocks and minerals.
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Galapagos Islands
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Homology
• Genetic: even the codons (3 base code for each amino acid) are preserved across wide arrays of organisms.
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Homology–Developmental
• Human coccyx • Gill pouches in Tetrapods
(p. 512) • Goethe and the sutures in
the skulls of apes and humans.
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Structural/developmental homology
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Structural homology–cont’d
• Bone for bone homology (some fusion/loss) across array of Tetrapods
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Origin of Adaptation
• Originally thought of as design: God conferred appropriate structures on organisms. Chain of Being.
• Lamarck proposed Evolution to explain the nested pattern of similarity. Mechanism: use and disuse (organismal drive or will) and inheritance of acquired characteristics.
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Darwin 1809–1882
• Malthus’ essay on population growth invoked the idea of competition in a high mortality environment.
• Developed an explicit model model of natural selection.
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Natural selection
• Organisms in a population vary with respect to various traits.
• Some of this variation is heritable.
• In each generation more individuals are produced than can survive (struggle for existence)
• The subset that survive each generation will be enriched for heritable variation that allow them to outcompete other variants.
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Natural selection and antibiotic resistance.
• Mycobacterium tuberculosus
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TB an important disease
• ~25% of deaths in NY City in 1804.
• Treatment in early 20th century: pneumothorax and rest.
• With advent of antibiotics, TB declined in 1950s.
• Began to increase again in 1980s and 90s.
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Oft repeated scenario…
• Individual enters hospital with symtoms of TB.
• Treated and observed for a number of weeks until judged cured.
• Returns some months later with renewed case of TB–unresponsive to antibiotics.
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What happened?
• Did variation exist in the original infecting population?
• Was the variation heritable? • Did the new variant affect reproductive
success? • Did selection occur?