Biology 106: Lecture # 6 Darwin's Theory: The Origin of Species

I. Importance -Theory explains enormous diversity of life -Provides unity to Biology

II. Pre-Darwin in the 19th century

A. Creationism: ex. John Ray (1628-1705) Each species represents a divine act

B. Evolution Pre-Darwin

1. Linneaus (1707-1778): Binomial nomenclature

2. Lamarck (1744-1829)

3. Lyell (geologist): a. Bible- earth 5000 years old;

III. Charles Darwin (1809-1882)

A. Voyage of the Beagle (1831-1836)

1. observed and collected plants and animals along coast and islands of S. hemisphere: most famous stop: Galapagos Islands

B. Darwin's return to England: publ. works of natural history and classification; formulated ideas on evolution but a young hot shot WALLACE!!! (1823-1913) also came up with the same ideas!

1858: both papers read at SAME meeting; publication of book "Origin of the Species" 1859

IV. Darwin's (and Wallace's) Theory

A. Organisms have changed

B. Species are related because they share common ancestor

C. Change occurs slowly, but earth is old

D. Mechanism: NATURAL SELECTION via Differences in surv. and repro. among individuals

1. BOTH invoke Malthus's ideas

a. populations increase geometrically: 2-4-8-16-32-64-128 etc., but food supply increases arithmetically: 1-2-3-4-5-6-7-8, etc.

b. unchecked reproduction = overpopulation

c. nature acts to check popln. growth through increased mortality

2. Principles of Natural Selection

a. more offspring produced that can themselves reproduce

b. variation among individuals in survival and repro.

c. variation is heritable - offspring resemble parents, gen. var.!

d. differences in surv. and reprod. is based on genetic variation

V. Darwin's Evidence:

A. Artificial Selection; B. Age of Earth; C. Macroevolution (large changes); D. Microevolution (small changes); evolution = change in gene frequency within a population across generations/through time.

E. Anti-Natural Selection Jenkins (1867): Pointed out flaw in blending inheritance- trait favored by NS would be lost!; Places importance on mutation.

VI. After Darwin (1880-1920): Blending theory remains prevalent and mutations important!

NeoDarwinism (1930-1940's): by Fisher, Wright, Haldane, Dobzhansky, and others.

1. Reconciliation of Darwin's theories with Mendel laws of particulate inheritance; 2. recombination and indep. assortment release genetic variation; 3. Natural Selection causes gene freq. to change, increasing survivorship and reprod of indiv.; 4. Adaptation through Natural Selection; 5. New alleles of genes arise by mutation;

6. Mutant alleles are often recessive.

Natural Selection: 1. Selection acts directly on the phenotype

2. Two Components of Fitness = repro. contribution to future generations

a. Fitness of a phenotype = indiv. fitness: the quantity and quality of progeny that one contributes to the next generation.;

b. Kin selection = related offspring helped by an indiv.

c. Inclusive Fitness = indiv. + kin

3. Forms of Natural Selection:

a. Directional =

b. Stabilizing or Balancing =

c. Disruptive or Diversifying =

d. Frequency Dependent =

4. Limits to Selection =