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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 sustained
c. 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: prokaryotes
next: early eukaryotes
next: fish
next: amphibians
next: reptiles
next: mammals
next: birds
Biogeography
1. geographic distribution of species suggests evolution
from common ancestors
2. Galapagos and South America
3. Australian marsupials
Comparative Anatomy
1. Homologous structures
from common ancestor
Comparative Anatomy
1. Homologous structures
from common ancestor
2. Analogous structures (15.14)
similar structures as the result of separate lineages
flippers of dolphins and penguins
Comparative Anatomy
3. Vestigial structures
non-functional structure inherited from ancestor
served 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 mexicanus
Blind cave-dwelling fish
Dandelions have sex organs, but don’t use them.
Virgin female whiptail lizards (several species)
unisexual: all female
will still occasionally “mount” other females
Comparative Embryology
1. embryos among some species very similar
2. all vertebrate embryos almost indistinguishable at
certain stages
Molecular Record
1. as organisms change, so should their genes
2. the more change  the more alterations in the
nucleotide sequence over time
3. select a gene to study
a. organisms more distantly related have greater numbers
of differences in their genes
b. closer relatives, fewer differences
4. molecular family trees
a. support the fossil record
b. confirm the “clusters” seen in the fossil record