a201-11f-05-ElephantsAndEpistemology - Introduction to...

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Introduction to Biological Anthropology: Notes 5 Elephants and epistemology Copyright Bruce Owen 2011 - Organisms with short generations tend to evolve faster than those with long generations - Because evolutionary change happens due to selection among members of one generation - some survive to adulthood, others don’t - some reproduce a lot, others don’t - the shorter the time between generations - the more rounds of selection occur in a given period of time - illustration: - the average age at which an American woman gives birth is about 25 years old - many births come at younger ages, and many at older, but this is the average age of motherhood - so American humans go through one round of selection every 25 years - the average age at which a fruit fly lays eggs is about two weeks - so fruit flies go through over 650 rounds of selection in those same 25 years - we should expect fruit flies to evolve more rapidly than humans - Imagine selection that causes an organism’s size to increase 1% per generation - this is strong selection, but still only a fraction of what was observed to happen with the beak depth of medium ground finches on Daphne Major - if this degree of selection affected humans, individuals in the population would average 1% taller in 25 years (one generation) - if this degree of selection affected fruit flies, individual fruit flies in the population would average 644 % larger (over 6 times larger) in 25 years (650 generations) - so we generally think of… - bacteria that can reproduce many times per day - insects that reproduce many times per year - or small animals likes mice that reproduce several times per year - as evolving rapidly - and large, long-lived mammals like humans or elephants as evolving much more slowly - But even large, long-lived mammals can evolve faster than we usually think - if the selection pressure is strong enough - selection pressure : the intensity of selection. - if deeper-beaked birds are 1% more likely to survive and reproduce, that might be a moderate selection pressure - if deeper-beaked birds are three times more likely to survive and reproduce, that would be a stronger selection pressure - here is a real-life example of rapid evolutionary processes in a large, long-lived mammal - Main source: BBC News, September 25, 1998 - Elephant poaching for ivory has been intense in most of Africa since at least the 19 th century - In 1930, about 1% of elephants in Uganda were born without tusks - this would normally be seen as a birth defect
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This note was uploaded on 03/02/2012 for the course ANTHRO 201.3 taught by Professor Owen during the Fall '11 term at Sonoma.

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a201-11f-05-ElephantsAndEpistemology - Introduction to...

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