Chapter 3: Darwinian Natural Selection

1)   Charles Robert Darwin (1809 c 1882)

a.    1831 was a naturalist on Beagle

b.    Traveled widely throughout the Atlantic and Pacific

c.     1838 starts discussing the theory of natural selection

d.    1859 published "On the Origin of Species"

2)   Alfred Russel Wallace (1823-1913)

a.    Naturalist working extensively in South America

b.    1858 sent Darwin a copy of his manuscript "ON the Tendency of Varieties to Depart Indefinitely from the Original Type"

Both worked on discerning the PROCESS of speciation by looking at the PATTERN of speciation.

3)   1900 Gregor Mendel demonstrates the particulate nature of inheritance (not blending).

4)   1953 James Watson and Francis Crick published the structure of the material of inheritance (i.e., DNA).

1)   Individuals within species are variable

2)   Some of these variations are passed on to offspring

The graph below would indicate that the character was strongly influenced by genetics

Below would indicate that the character was not strongly influenced by genetics

3)   In every generation, more offspring are produced than can survive.

4)   The survival and reproduction of individuals are not random: The individuals who survive and reproduce are those with the most favorable variations.

As a result there is a change in the frequency of characters from one generation to the next. These characters confer increased fitness on the individuals that possess them.

Increased fitness is only RELATIVE to others in the population

1)   Natural Selections Acts on Individuals, but the consequences are to the population (or species) not the individual.

a.    Individuals don t evolve.

2)   Natural Selection Acts on the Phenotype, but Evolution is the change in heritable variation.

a.    Changes in frequency of non heritable characters are not evolution (cold and body size).

3)   Natural Selection is backward looking, not forward looking.

a.    Because something may be useful tomorrow is not natural selection

4)   Natural Selection Can Produce New Traits, Even Thought it Acts on Existing Traits.

a.    Horse's leg

5)   Natural Selection is NOT Perfect or Optimal

a.    Relative fitness differences is important

6)   Natural Selection is non random, but it is Not progressive

a.    E. coli is a good bacteria and you are a very bad bacteria

7)   Fitness is not Tautological (circular)

a.    Fitness is a correlation

8)   Natural Selection Acts on Individuals Not Groups

a.    i.e., there is no such thing as Altruism (actions that while decreasing the actors fitness increase the groups).

b.    This point is arguable

1)   As a result of mutation creating new alleles, and segregation and independent assortment shuffling alleles into new combinations, individuals within populations are variable for nearly all traits.

2)   Individuals pass their alleles on to their offspring intact.

3)   In most generations, more offspring are produced than can survive.

4)   The individuals that survive and go on to reproduce, or who reproduce the most, are those with the alleles and allelic combinations that best adapt them to their environment.