http://www.biology.lsu.edu/webfac/kharms/BIOL1202Fall2007.htm

Course website:

BIOL 1202, Section 1 Dr. Kyle Harms

http://www.biology.lsu.edu/webfac/kharms/BIOL1202Fall2007.htm

First Exam Score versus Attendance

0

2

4

6

8

10

12

14

16

20-29 30-39 40-49 50-59 60-69 70-79 80-89 90-99

Attended all

Missed 66% or More

Final exam score

In BIOL 1202, good attendance pays off! Pro

port

ion o

f st

ud

ents

Chapter 22

Descent with Modification: A Darwinian View of Life

Why are there so many species?

The Theory of Evolutionby Natural Selection

Charles Darwin

Hypothesis vs. Theory

Hypothesis

Tentative explanation of observations

Educated guess

General explanation of important natural phenomena, developed through extensive & reproducible observations & experiments

Theory

Western Historical Context

Aristotle (384-322 B.C.) – Greek philosopher

Species are permanent, perfect, immutable

Dominant world view for

> 2000 yr

See timeline Fig. 22.2

Western Historical Context

Species are permanent, perfect, immutable

A.D. – Natural Theology (Creationism)

See timeline Fig. 22.2

Western Historical Context

Swedish physician & botanist whose passion was taxonomy

Carolus Linnaeus (1707-1778)

Developed a hierarchical classification scheme & binomial nomenclature

See timeline Fig. 22.2

Western Historical Context

Carolus Linnaeus (1707-1778)

“King Philip Came Over For Gumbo

Sunday”

Canis = genuslupus = specific epithet that refers to one species in the genus Canis

The binomial is always italicized or underlined, the genus name is always capitalized, and the specific epithet is always lower case

See Fig. 25.8

Western Historical Context

French anatomist who largely developed paleontology, the study of fossils

Georges Cuvier (1769-1832)

See timeline Fig. 22.2

Western Historical Context

Georges Cuvier (1769-1832)

Deeper strata contain older taxa

See timeline Fig. 22.2

Western Historical Context

Georges Cuvier (1769-1832)

Preferred hypothesis for profound geologic change = catastrophism

See timeline Fig. 22.2

Western Historical Context

Scottish geologist who offered an alternative to catastrophism

James Hutton (1726-1797)

Preferred hypothesis for profound geologic change = gradualism

See timeline Fig. 22.2

Western Historical Context

Scottish geologist who incorporated Hutton’s gradualism into the theory of uniformitarianism

Charles Lyell (1797-1875)

See timeline Fig. 22.2

Western Historical Context

Charles Lyell (1797-1875)

Uniformitarianism – geological processes & rates today are those that also operated in antiquity

See timeline Fig. 22.2

Western Historical Context

Charles Lyell (1797-1875)

Uniformitarianism – suggested that the Earth is > 6000 yr old

See timeline Fig. 22.2

Western Historical Context

Jean Baptiste Lamarck (1744-1829)

Invertebrate Curator ofthe Natural History Museum in Paris

One of the 18th & 19th centuries’ biologists who hypothesized that traits of species are not immutable, i.e., they can evolve

See timeline Fig. 22.2

Western Historical Context

Jean Baptiste Lamarck (1744-1829)

Hypothesized mechanism of evolution: Use & disuse alters traits; inheritance of acquired characters results in adaptations to environmental conditions

See timeline Fig. 22.2

Western Historical Context

Thomas Malthus (1766-1834)

English demographer

Hypothesis: Plants and animals are capable of producing far more offspring than resources can support; the “struggle for existence” (e.g., famine, war) is an inescapable consequence

See timeline Fig. 22.2

Within this context, Charles Darwin (1809-1882) served as Ship’s Naturalist on the HMS Beagle’s

circumnavigation of the globe (1831-1836)

Western Historical Context

EnglandEUROPE

NORTHAMERICA

GalápagosIslands

Darwin in 1840,after his return

SOUTHAMERICA

Cape ofGood Hope

Cape Horn

Tierra del Fuego

AFRICA HMS Beagle in port

AUSTRALIA

TasmaniaNewZealand

PACIFICOCEAN

An

des

ATLANTICOCEAN

Galapagos Islands, Ecuador

Galapagos Islands, Ecuador

Galapagos Islands, Ecuador

Galapagos Islands, Ecuador

Darwin was a good observer of both wild and domesticated organisms (e.g., birds)

Darwin was a good observer of both wild and domesticated organisms (e.g., birds)

Western Historical Context

Charles Darwin (1809-1882)

English gentleman who conceived of natural selection as the principal mechanism of adaptive evolution

See timeline Fig. 22.2

Western Historical Context

Alfred Russel Wallace (1823-1913)

English biologist who also (independently) conceived of natural selection as the principal mechanism of adaptive evolution

See timeline Fig. 22.2

Lyell presented the independently derived hypothesis to the

Linnaean Society of London on July 1, 1858

Western Historical Context

Western Historical Context

Charles Darwin (1809-1882)The Origin of Species(1859)

“It is interesting to contemplate an entangled bank, clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other, and dependent on each other in so complex a manner, have all been produced by laws acting around us…

There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed laws of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.”

The Origin of SpeciesFinal paragraph:

Darwinian Theory of EvolutionDescent with modification

Descent implies common ancestry

Modification to better suite the environment =

adaptation

Natural selection is the principal process that drives adaptive

evolutionSee Fig. 22.7

Darwinian Theory of EvolutionOrganisms have enormous potential for population

increase, but the potential is rarely reachedGeneralized sigmoidal population growth curve

Potential for rapid population growth when resources

are not limiting

Resource availability generally limits population size

Competition for resources(“struggle for existence”)

Phenotypic variability (morphology, physiology,

behavior, etc.)

Natural Selection: Survival and reproduction of the

“fittest” individuals

Some variabilityresults from heritable

differences

Adaptive evolution: A change in the phenotypic constitution of a population owing to selection on heritable variation

among phenotypes

Use Inheritance of acquired

characteristics

Generation 1 Generation 2

Naturalselection

Genetic inheritance from

selected population

Lamarckism

Darwinism

Darwin used artificial selection to illustrate the modifying potential of selection

Evidence for the Theory of Evolution by Natural Selection

Darwin used artificial selection to illustrate the modifying potential of selection

Evidence for the Theory of Evolution by Natural Selection

Darwin used artificial selection to illustrate the modifying potential of selection

Evidence for the Theory of Evolution by Natural Selection

Evidence for the Theory of Evolution by Natural Selection

Rapid changes in populations under strong selection

E.g., pesticide resistance

Homologous traits (a.k.a. characters, attributes) = traits in different species that arose from the same ancestral trait

(may or may not have similar function)

See Fig.

22.14Human Cat Whale Bat

Evidence for the Theory of Evolution by Natural Selection

Even when homologies are not obvious in adults, they may be quite apparent in embryonic stages

Lemur Pig Human

Which one is the human?

Evidence for the Theory of Evolution by Natural Selection

Analogous traits = traits in different species that have similar function, but arose from different ancestral traits

Evidence for the Theory of Evolution by Natural Selection

doesn’t matter as much as the evolutionary history of the

traits themselves

To distinguish homologous vs. analogous traits, the relatedness of the organisms

Analogous traits = traits in different species that have similar function, but arose from different ancestral traits

Evidence for the Theory of Evolution by Natural Selection

Vestigial organs = remnants of organs that had important functions in ancestors

These examples happen to be

homologous leg and foot bones

Evidence for the Theory of Evolution by Natural Selection

Vestigial organs = remnants of organs that had important functions in ancestors

Evidence for the Theory of Evolution by Natural Selection

Biochemical homologies

Common use of DNA, RNA, amino acids, ribosomes, genetic code, ATP, electron carriers, electron transport

system, etc.

Evidence for the Theory of Evolution by Natural Selection