C. Thomas Malthus (an economist) 1. Essay on the Principles of Population (1798)

a. populations of organisms increase geometrically b. rate of reproduction too high to be sustainedc. warning against human overpopulation

2. but in nature, this does not seem to occur 3. Darwin’s answer: death (selection) limits population numbers 4. This provided missing link for Darwin

D. Alfred Wallace 1. came to same conclusions while in Indonesia 2. published his findings along with Darwin (1858-59)

E. Darwin: On the Origin of Species by Means of Natural Selection 1. descent with modification 2. closely related species likely from common ancestor

Darwin’s Theory

Hypothesis 1: Every organism has the potential to leave more than one offspring.Hypothesis 2: The number of individuals within a species remains fairly constant over time.Prediction A: If 1 and 2 are true, then not all individuals realize their reproductive potential.

Hypothesis 3: Individuals within a species vary in terms of their traits.Hypothesis 4: At least some of these traits are inherited.

Prediction B: If A, 3, and 4 are true, then some individuals are better suited for their environment, leaving more offspring. Their traits become more common.

Darwin’s Theory

Better suited individuals have inherited those traits, and they pass them on to their offspring.Survival of the fittest = Reproduction of the fittest.

What is the evidence for evolution?

Silurian and Devonian fishes (Modified from Fenton and Fenton, 1958)Jurassic and Cretaceous fishes (Modified from Romer, 1966)

Radiometric dating (Section 15.5 in the text)

Half-life of 14C is 5,730 years

(Modified from Bushee and others, 2000)

(Modified from Bushee and others, 2000)

Biostratigraphy: The science that deals with the distribution of fossils in the rock record and organizes strata into units on the basis of their contained fossils.

The oldest layer is on the bottom. Rocks were deposited one layer at a time from the bottom up.

(Pojeta and Springer, 2001)

The combination of strata and radiometric dating clearly demonstrates progressive change in the fossil record.

(Modified from Ward and Blackwelder, 1975)

Organisms have evolved in a historical sequence.oldest: prokaryotesnext: early eukaryotesnext: fishnext: amphibiansnext: reptilesnext: mammalsnext: birds

Biogeography1. geographic distribution of species suggests evolution from common ancestors

2. Galapagos and South America

3. Australian marsupials

Comparative Anatomy

1. Homologous structuresfrom common ancestor

Comparative Anatomy1. Homologous structures

from common ancestor

2. Analogous structures (15.14)similar structures as the result of separate lineagesflippers of dolphins and penguins

Comparative Anatomy3. Vestigial structures

non-functional structure inherited from ancestorserved a useful purpose in the ancestor

Human Appendix

Human arrector pili muscles and body hair

Human Coccyx

Muscles that move the ears

Wisdom Teeth

Wings on flightless birds

Astyanax mexicanusBlind cave-dwelling fish

Dandelions have sex organs, but don’t use them.

Virgin female whiptail lizards (several species)unisexual: all femalewill still occasionally “mount” other females

Comparative Embryology

1. embryos among some species very similar2. all vertebrate embryos almost indistinguishable at certain stages

Molecular Record

1. as organisms change, so should their genes2. the more change the more alterations in the nucleotide sequence over time

3. select a gene to studya. organisms more distantly related have greater numbers of differences in their genesb. closer relatives, fewer differences

4. molecular family treesa. support the fossil recordb. confirm the “clusters” seen in the fossil record