Biogeography Size of the known world expanded enormously in 15th century Accepted beliefs did not explain discovery of new organisms in previously unknown.

Biogeography

• Size of the known world expanded

enormously in 15th century

• Accepted beliefs did not explain discovery

of new organisms in previously unknown

places

Biogeography

Comparative Morphology

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

• Puzzling patterns:– Animals as different as whales and bats

have similar bones in forelimbs – Some parts seem to have no function

coccyx

ankle bone

fossilized ankle bone

Comparative Morphology

Geological Discoveries

• Similar rock layers throughout world

• Certain layers contain fossils

• Deeper layers contain simpler fossils than

shallow layers

• Some fossils resemble known species

19th Century: New Theories

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

• Two examples– Georges Cuvier: multiple catastrophes– Jean Lamarck: inheritance of acquired

characteristics

The Theory of Uniformity

• Lyell’s Principles of Geology

• Earth shaped by subtle, repetitive processes of change

• Challenged the view that Earth was only 6,000 years old

Darwin’s Voyage

• At age 22, Charles Darwin began a five-year, round-the-world voyage aboard the HMS Beagle

• As ship’s naturalist, he collected and examined species that inhabited regions the ship visited

Darwin’s Voyage

Fossil Evidence

• Darwin found fossil Glyptodont

• Proposed descent with modification

Voyage of the Beagle

EQUATOR

GalapagosIslands

GalapagosIslands

Isabela

Darwin

Wolf

Pinta

Marchena Genovesa

Fernandia

SantiagoBartolomé

RabidaPinzon

SeymourBaltra

Santa Cruz

Santa Fe

Tortuga

Española

San Cristobal

Floreana

•Volcanic islands far off coast of Ecuador

•All inhabitants are descended from species that arrived on islands from elsewhere

Malthus: Struggle to Survive

• Thomas Malthus, a clergyman and economist, wrote essay that Darwin read on his return to England

• Argued that as population size increases, resources dwindle, the struggle to live intensifies, and conflict increases

Galapagos Finches

• Darwin observed finches with 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

Galapagos Finches

Reproductive Capacity and Competition

• All populations have the capacity to increase in numbers

• No population can increase indefinitely

• Eventually, individuals of a population end up competing for resources

Variation in Populations

• All individuals have the same genes that specify the same assortment of traits

• Most genes occur in different forms (alleles), which produce different phenotypes

• Some phenotypes compete betterthan others (fitness)

Change over Time

• Over time, alleles that produce the most successful phenotypes will increase in the population

• Less successful alleles will become less common

• Change leads to increased fitness– Increased adaptation to environment

Natural Selection

• Natural selection for various traits among individuals of a population affects which individuals survive and reproduce in each generation

• Process results in adaptation to the environment (increases fitness)

Alfred Wallace

• Naturalist who arrived at the same conclusions Darwin did

• Wrote to Darwin describing his views

• Prompted Darwin to finally present his ideas in a formal paper

Adaptation

• Some heritable aspect of form, function, or behavior that improves the odds for surviving and reproducing

• Environment specific

• Outcome of natural selection

Adaptation to What?

• Llamas live at high altitude and have hemoglobin with a high oxygen affinity

• Is this an adaptation to altitude?Probably not

• Llamas are related to camels, which live at low altitudes

• Camels also have hemoglobin with high oxygen-binding capacity

Common Ancestors

• Llama and camel

Populations Evolve

• Biological evolution changes populations, not individuals

• Traits in a population vary among individuals

• Evolution: change in the frequency of traits

The Gene Pool

• All the genes in a population

• Genetic resource that is shared (in theory) by all members of population

Variation in Phenotype

• Each gene in gene pool may have two or more alleles

• Individuals inherit different allele combinations– leading to variation in phenotype

• Offspring inherit genes, not phenotypes

What Determines Alleles in a New Individual?

• Mutation

• Crossing over at meiosis I

• Independent assortment

• Fertilization

• Change in chromosome number

or structure

Reproductive Isolation

• Cornerstone of the biological species concept

• Speciation is the attainment of reproductive isolation

• Reproductive isolation arises as a by-product of genetic change

Biological Species Concept

• “Species are groups of interbreeding natural populations that are reproductively isolated from other such groups.”