Evolution

Theories of Evolution

Jean Baptiste Lamarck

• similar species

descended from a common ancestor

• stated acquired traits were passed to

offspring (traits not determined by genes,

they are the result of an organism's

experience) – “Lamarckism”

– The environment made a structure useful or

useless, which in turn, caused the structure

to change

Theories of Evolution

Darwin & Wallace

• species were modified by natural

selection

– organisms best fit to survive in their

environment survive to reproduce

– “Survival of the Fittest”

• Fitness is how well an organism survives

and reproduces

Darwin

Wallace

Charles Darwin • Charles Darwin was the

naturalist on the HMS

Beagle. While on the ship,

he gathered the

observations that lead to the

theory of evolution through

natural selection. His ideas

were published in the book,

“On the Origin of Species by

Natural Selection.”

• Darwin stated: Over a long

time, nature determines

what traits/adaptations are

the most beneficial for a

species.

Darwin's Theories

• Descent with modification- newer

forms appearing in the fossil record are

actually the modified descendents of

older species

• Modification by natural selection-

Natural Selection vs. Artificial

Selection

– Natural: organisms with helpful traits

survive and reproduce to pass their

traits on. “Nature chooses”

– Artificial: organisms with specific

traits are selected and bred. “Man

chooses”

Adaptations Adaptations-

- Any heritable characteristic that

increases an organism’s ability to

survive and reproduce

- structural

- physiological

- behaviorial

Adaptations Structural Adaptation

Example: Camouflage

-Pepper Moths were once whitish with

black spots to blend with trees and

hide from predators. The Industrial

Revolution gave off so much pollution

that the trees turned black with soot.

A “mutated” blackish Pepper Moth that

would have been eaten on a white tree

survived to pass on its genes. Pepper

Moths are now blackish in color.

Adaptations Structural Adaptation

Example: Camouflage – Pepper Moths

Adaptations Structural Adaptation

Example: Mimicry

Adaptations Physiological Adaptations

– Venom in snakes

– Ink in sea hares

– Adaptations involving water

conservation in desert animals

Behavioral Adaptations

– Honey bee dances

– Mating rituals

Evidence of Evolution 1. Fossils- (there are holes in the record)

– Fossil- any trace of a long dead organism

usually found in sedimentary rock

– Fossil types

• mold- an imprint in rock in the shape of

an organism

• cast- a rocklike model of the organism

Law of Superposition- the oldest stratum is

the lowest and the youngest stratum is the

top layer

Biogeography- the study of the geographical

distribution of fossils & living organisms

Fossils & The Law of Superposition

Biogeography

Evidence of Evolution 2. Anatomy-

– homologous structures- looking for parts that are

similar in structure or function (from common

ancestry)

– analogous structures- parts that are alike in

function (NOT from common ancestry)

– vestigial structures- a structure that has no function

in today’s organism, but had a function in its

ancestors.

Evidence of Evolution 3. Embryology- comparison of embryos

Chicken

Fish

Turtle

Salamander

Pig Cow Rabbit Human

Evidence of

Evolution 4. Biochemistry-

comparison

of similarities

in DNA, RNA,

and

biochemical

functions

PATTERNS OF EVOLUTION 1. Divergent Evolution- species that were once

similar become increasingly

different

Adaptive Radiation- when an

ancestral species develops

an array of species

(Darwin’s Finches)

• This is a type of

divergent evolution

PATTERNS OF EVOLUTION 2. Convergent Evolution- species

that were once different

become increasingly similar

PATTERNS OF EVOLUTION

• Coevolution- the change of 2 or

more species in close association

with each other

Allele Frequencies Populations evolve, NOT INDIVIDUALS!

• Population- all members of a species

that live in an area.

• All alleles of a population are known as

the gene pool.

• The percentage of any specific allele is

the allelic frequency.

• If allelic frequencies do not change,

the population is in genetic

equilibrium.

Mechanisms That Change Genetic Equilibrium

1. Mutation

- chance (when DNA is copied)

- environmental factors (radiation, chemicals, etc.)

2. Genetic Drift

- chance events divide a population (volcanoes,

earthquakes, etc.) – this results in geographic isolation

- immigration & emigration resulting in gene flow

Mechanisms That Change Genetic Equilibrium

3. Small Population Size

- Bottleneck Effect – a change in allele

frequency following a dramatic reduction in the

size of a population

Mechanisms That Change Genetic Equilibrium

3. Small Population Size

- Founders Effect – allele frequencies change as

a result of the migration of a small subgroup of

a population

Mechanisms That Change Genetic Equilibrium

4. Non-random Mating

- sexual selection – organisms select mates for

size, color or another specific trait

Mechanisms That Change Genetic Equilibrium

5. Natural Selection

• There are 3 types of natural selection.

a. Stabilizing Selection- average individuals are favored

b. Directional Selection- one extreme variation of a trait is

favored

c. Disruptive Selection- individuals with extreme variations

of a trait are favored

Hardy Weinberg Principle

Hardy Weinberg Principle

Allele Frequencies in a population should remain

constant

p2 + 2pq + q

2 = 1 AND

frequency A + frequency a = 100

frequency AA + frequency Aa + frequency aa = 100

Speciation • Speciation- the evolution of a new

species

• Species- a population of organisms

that can successfully interbreed to

produce fertile offspring

Causes of Speciation

1. Geographic Isolation

2. Reproductive Isolation

- Temporal Isolation

3. Polyploidy

4. Behavioral Isolation

Evolution Ideas 1. Gradualism- the idea that a species originate

through a gradual change of adaptations

2. Punctuated Equilibrium- speciation occurs in

rapid bursts with long periods of genetic

equilibrium between bursts