Module 1: Evolution

Month Day TopicAug 28 History of life on Earth

30 Theory of evolution

Sept 1 Timeline construction

4 Holiday

6 Evidence for evolution

8 Mechanisms of evolution I

11 Mechanisms of evolution II

13 Speciation

Outline

1. History

2. Cultural and scientific context of Darwin’s theory of evolution

3. The theory

4. Modern ideas

Organic evolution

The descent of modern organisms with modification from preexisting life-forms

Time

• Cosmological

• Geological

• Evolutionary

• Ecological

• Physiological

Hierarchy of scientific information

Theory

Fact

Model

Hypothesis

Hypothesis--a limited statement implying cause and effect in certain situations.

Model--a hypothesis that has been shown to have more general validity.

Fact–a highly corroborated hypothesis that has been so repeatedly tested and for which so much reliable evidence exists, that it would be perverse or irrational to deny it.

Theory or Law—unification of facts. A unifying and self-consistent explanation of fundamental natural processes or phenomena that is totally constructed from facts.

Cultural and scientific context of the theory of evolution

Idea of fixed species

• Ancient Greeks (2500 years bp): – species do not change

Idea of fixed species

• Ancient Greeks (2500 years bp): – species do not change

• Judeo-Christian (2000 years bp): – species do not change– each species divinely created– earth ~ 6000 years old

Confounding Evidence

• Biogeography

• Comparative anatomy

• Geologic discoveries

Confounding evidence: Biogeography

• Size of the known world expanded in the

15th century

• Discovery of new organisms could not be

explained by accepted beliefs

– How did species get from center of creation

(e.g., garden of Eden) to all these places?

Confounding evidence: comparative morphology

• Study of similarities and differences in body plans of major groups

• Puzzling patterns:– Animals as different as humans and dogs

have similar bones in forelimbs

– Some parts seem to have no function

backbone

pelvic girdle

coccyx (boneswhere manyother mammalshave a tail)

small boneattached topelvic girdle

thighboneattached topelvic girdle

Geological Discoveries

• Similar rock layers throughout world

• Certain layers contain fossils

• Deeper layers contain simpler fossils than

shallow layers

• Some fossils seem to be related to known

species

1800s - New Theories

• Scientists attempt to reconcile evidence of change with traditional belief in a single creation event

•Two examples–Georges Cuvier (1769-1832) - multiple catastrophes

–Jean Lamarck (1744-1829) - inheritance of acquired characteristics

The New Geology

• Hutton and Lyell (1830s):– Uniformitarianism: the present is the key to

the past

–Gradualism: slow process over vast periods of time can cause big changes

–Earth is seriously old!

Principles of populations

• Thomas Malthus (1766-1834):– Exponential growth of populations

Principles of populations

• Thomas Malthus (1766-1834):– Exponential growth of populations– “Positive checks” on population growth

• War• Disease• Famine

– As populations increase, resources dwindle, the struggle to live intensifies, and conflict increases

Charles Darwin (1809-1882)

• Collected and examined the species that inhabited the regions the ship visited

• Started 5 year, round-the-world voyage aboard the Beagle at age 22

The voyage of H.M.S. Beagle

Pleistocene glyptodont

Modern armadillo

Evolution:Descent with modification

But what causes modification?

What is the mechanism?

Galapagos Finches

• Darwin observed a variety of lifestyles and body forms

• On his return, he learned that there were 13 species

• He attempted to correlate variations in their traits with environmental challenges

Darwin’s facts• Any species is capable of increasing its

population exponentially

• BUT we rarely see this increase—populations

tend to stay within certain limits

• Conclusion: not all offspring produced survive

• Conclusion: there is a “struggle for existence”

going on in all species

Darwin’s facts• Individuals in any species vary

• Some vary in ways that help them survive and

reproduce; others vary in ways that decrease

their chances of survival

• Variation is inherited (somehow)

• Conclusion: a species will change over time,

producing new and different varieties (evolution)

Darwin’s theory

– Fact #1: Overproduction and struggle for existence

– Fact #2: Heritable individual variation

The inescapable conclusion: Differential or unequal reproductive success

causes evolution. He called this natural selection.

Artificial selection as an analog of natural selection

Natural selection

• Charles Darwin (1830-1850s): Ruminated on theory, but didn’t publish

• Alfred Wallace (1850s): Independently developed a theory similar to Darwin’s

• Darwin and Wallace “co-published” the theory in 1858

• Darwin published The Origin of Species in 1859

Evolution:Descent with modification

Evolution:Descent with modification

Natural selection: Differential reproductive success

Evolution:Descent with modification

Natural selection: Differential reproductive success

Darwin’s theory

– Fact #1: Overproduction and struggle for existence

– Fact #2: Heritable individual variation (no clear mechanism yet)

The inescapable conclusion: Differential or unequal reproductive success

Ever since Darwin...

Ever since Darwin...• Mendel develops theory of heredity (1860s)

– Parents pass onto their offspring discrete, heritable factors that are responsible for inherited traits.

– Discrete, heritable factors = genes– Genes act in predictable ways

Ever since Darwin...• The “Modern Synthesis” (mid-1900s):

– Often called “Neo-Darwinism”– Adding in population genetics– Mathematical models of evolution

Ever since Darwin...• The molecular era (mid 1900s-present)

– Discovery of DNA as the basis of heredity– Adding in a molecular mechanism– Detecting the relationships among species

Ever since Darwin...• The era of genomics (1990s-present)

– Mapping of genomes– Rapid sequencing of genes– Creation of molecular phylogenies