Natural Selection

Natural Selection - What is Natural Selection? WFC 10...

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1 What is Natural Selection? WFC 10 Nothing in biology makes sense except in the light of evolution Theodosius Dobzhansky 1973 Basic precepts of Natural Selection Variation Organisms vary! Why? 1 Environmental factors such as food, climate 2 Genetic factors , that is, inherited differences Of course, both factors may be involved. Student Heights 4.5 5.0 5.5 6.0 6.5 7.0 0 5 10 15 20 Mother 4.5 5.0 5.5 6.0 6.5 7.0 Frequency 0 5 25 30 Father Height (ft) 4.5 5.0 5.5 6.0 6.5 7.0 0 5 Your heights generally lie between those of your parents And they are positively related to the average of your parent’s heights The positive relationship reflects genetics The scatter, or “noise,” around this line reflects the environment 4.5 5.0 5.5 6.0 6.5 7.0 0 5 4.5 5.0 5.5 6.0 6.5 7.0 0 5 4.5 5.0 5.5 6.0 6.5 7.0 0 5 WFC 10 -- Fall 2007 Mid-Parent Heights 5.0 5.2 5.4 5.6 5.8 6.0 6.2 6.4 Student Heights 4.6 4.8 5.0 5.2 5.4 5.6 5.8 6.0 6.2 6.4 6.6 6.8 r 2 = 0.26 And, this pattern is consistent, year after year after year . . . Fall 1998 -- r 2 = 0.22 56 4.5 5.0 5.5 6.0 6.5 4.5 5.0 5.5 6.0 6.5 Fall 2000 -- r 2 = 0.22 Fall 2005 -- r 2 = 0.28 Midparent Heights 4.5 5.0 5.5 6.0 6.5 Student Height 4.5 5.0 5.5 6.0 6.5 Fall 2001 -- r 2 = 0.27 4.5 5.0 5.5 6.0 6.5 4.5 5.0 5.5 6.0 6.5 Spring 2003 -- r 2 = 0.30 Fall 2002 -- r 2 = 0.26 5.0 5.5 6.0 6.5 4.5 5.0 5.5 6.0 6.5 Fall 2003 -- r 2 = 0.30 Mid-Parent Heights 5' 5'6" 6' Fall 2004 -- r 2 = 0.25 Fall 2006 -- r 2 = 0.23 4.5 5.0 5.5 6.0 6.5 Fall 2007 -- r 2 = 0.26 4.5 5.0 5.5 6.0 6.5
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2 Fall 1998 -- r 2 = 0.22 56 4.5 5.0 5.5 6.0 6.5 4.5 5.0 5.5 6.0 6.5 Fall 2000 -- r 2 = 0.22 Fall 2005 -- r 2 = 0.28 Midparent Heights 4.5 5.0 5.5 6.0 6.5 Student Height 4.5 5.0 5.5 6.0 6.5 Fall 2001 -- r 2 = 0.27 4.5 5.0 5.5 6.0 6.5 4.5 5.0 5.5 6.0 6.5 Spring 2003 -- r 2 = 0.30 Fall 2002 -- r 2 = 0.26 5.0 5.5 6.0 6.5 4.5 5.0 5.5 6.0 6.5 Fall 2003 -- r 2 = 0.30 Mid-Parent Heights 5' 5'6" 6' Student Heights Fall 2004 -- r 2 = 0.25 So, variation may be inherited. Why is this important? Consider the following example . . . Fall 2006 -- r 2 = 0.23 4.5 5.0 5.5 6.0 6.5 Fall 2007 -- r 2 = 0.26 4.5 5.0 5.5 6.0 6.5 Of all the organisms born, who survives? Let’s imagine a hypothetical rabbit 10 offspring per generation (5 male, 5 female) Generation # female offspring 1 1x5 = 5 2 5x5 = 25 3 25x5 = 125 4 125x5 = 625 . . 7 5 7 = 78,125 . . 10 5 10 = 9,765,625 . . 15 5 15 = 30,517,578,125 Generation 024681 0 1 2 1 4 Number of Female Bunnies (milions) 5 10 15 20 25 30 35 i.e., exponential growth If generation time were ca. 1 month . . . 60 billion rabbits within just over a year. Or, more mass than 20,000,000 elephants!! Another example – Atlantic Cod Average female produces about 2,000,000 eggs Larger females produce up to 5 million! However, 99% die within 1 month This leaves 20,000 90% of these die by their 1 st year Down to 200 By reproductive age – 2-4 years old – on average only 2 cod survive. This equals 0.0001% survival.
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This note was uploaded on 04/21/2008 for the course WFC 010 taught by Professor Moyle during the Fall '07 term at UC Davis.

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Natural Selection - What is Natural Selection? WFC 10...

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