Transcript notes
Evolution Controversies 19 September 2016 Evolution • Observation: That life changes through time • Mechanism: Variation, inheritance, selection; Darwin called this ‘natural selection’ or ‘survival of the fittest’ • Example: Index fossils. In a narrow layer, from a brief time • Consider ‘pop tops’ Evidence for Evolution • Vestigial organs • Intermediate forms, like archeopteryx • Convergent evolution: different history to same point • Even cars evolve, because customers select most appealing characteristics • But cars are designed, can we argue for ‘intelligent design’? Vestigial whale bones Archeopteryx is an intermediate form between reptiles and birds The pot top is an index fossil! Black peppered moth evolved in response to pollution Melanism in British Peppered Moths • • • • Birds are their major predator They settled on light, lichen-covered trees In 1848, less than 1% were dark But industrial revolution pollution killed the lichens, leaving dark trees • In 2000, more than 95% were dark • With pollution laws, now number of light moths increasing • This shows how air pollution drives evolution Rabbits and Myxomatosis • Rabbits are not native to Australia • In 1859, 12 wild European rabbits introduced • By 1886, spreading at 66 mi/year: Reached both coasts by 1907 • Nothing could stop the plague of rabbits; fencing, hunting, trapping did not work; they ate grass needed for sheep and cattle • Solution: mosquito-borne virus called myxomatosis : 1952 epidemic killed 99.9% What happened next? What happened next? • Viruses that were less deadly were selected, because their victims could infect others. The deadly ones killed the host, and left no descendants • Rabbits were also selected for greater resistance • Today, mortality is only 40% • All is explained by evolution of both virus and rabbit Convergent evolution of Mammals and marsupials Evolution of the Corvette Problems for Evolution • Not: Age of Earth, it is 4.5 billion years old. But… • Low probabilities: like a tornado going through a junk yard, leaving behind a 747; small changes to proteins and they don’t work • Gradualism: Gradual changes not seen in the fossil record: long stability, then sudden jump. Can we make a new species gradually? • Complexity: is it irreducible? Examples: human eye, blood clotting requires 12 chemical factors: one missing means hemophilia Replies to evolution questions • Low probabilities: Evolution is not random, selection works only on a useful subset; many other possibilities might work as well, remember convergent evolution on Earth • Gradualism: Fossil record is too poorly preserved; speciation takes longer than a human lifetime; but big random events may be needed • Complexity: Intermediate steps are actually useful; existing genes may be put to new uses; gradually improved; life may be like a Rube Goldberg machine, complicated, but it works Summary • Evolution is more than ‘just a theory’ • It is an established explanation, universally applied; arguments over details • Creationism is not science: an attempt to use scientific arguments to prove the Bible • Intelligent design is not required: Evolution is like a ‘blind watchmaker’ • But problems still: we can’t explain everything yet! Life found elsewhere could provide info