EVOLUTIONEVOLUTION

Jean Baptiste Lamarck

- One of the first to propose a hypothesis for how species can change.

“Theory of Acquired Characteristics”

- If an organism used a part of its body more, it grew

bigger (or changed).

- Any learned / acquired traits are then immediately passed on to their offspring.

Charles Darwin - Developed his ideas based on his 5

year voyage as a naturalist aboard the HMS Beagle.

- Wrote the book: On the Origin of Species

- Discovered more than 1500 species on the Galapagos Islands.

* What is a species?

- Darwin’s Observations:

* Noticed only slight differences between species on each island.

- Adaptations:

A trait which allows an organism to survive in its environment.

* Could be anything!

What can you say about each tortoise’s food supply?

- Darwin’s Theories:

1. Natural Selection

- When an individual(s), best suited for its environment, survives, mates & pass on its genes.

Factors Involved/Needed:

- Overproduction

- Variation

- Competition

- Those who can’t survive, die.

2. Artificial Selection

- When a breeder selects which traits are desirable, not the environment.

3. Survival of the Fittest

- Who is the most fit?

- The one’s who survive to produce the most “fertile” offspring.

III. Evidence for Evolution

A. Fossil Evidence

- What is a fossil?

* Trace of a long dead organism.

- How do they form?

* Organism dies and is quickly buried by sediment.

- How old they are?

1. Relative Dating

2. Absolute Dating (Half-Life)

- Types of Fossils:

1. Petrified

- Bone that has been changed to rock.

2. Molds & Casts

- Molds are hollow spaces in sediment.

- Casts are molds filled in with sediment.

3. Preserved Remains

- Organisms which have become fully preserved in materials such as ice or tree sap.

B. Homologous Structures

- Similar anatomical features shared between multiple species.

Humerus

Radius

Ulna Carpals & Metacarpals

Phalanges

C. Analagous Structures

- Different structures, same function.

D. Vestigial Structures

- Features which no longer serve a purpose.

E. Embryological Structures

- Similarity seen in early fetal development.

F. Biochemical Evidence

- Similarity in genetic material between different organisms.

Examples: DNA between Chimps & Humans

Proteins amongst various species

G. Transitional Species

Ex. Archaeopteryx

H. Bacterial Evolution in Action

• Bacteria evolves at such a fast rate due to it’s short lifespan.

• Many generations can be observed over a short period of time.

• Antibiotic resistant bacteria– MRSA

IV. Conditions which affect Gene Frequencies

A. The sum of all genes in a population is referred to as the Gene Pool.

B. If a population is in equilibrium, it will not evolve. Gene frequencies are

equal.

C. 5 Factors that Affect Gene Pools:

1. Mutations

- Introduces new alleles which can spread quickly if advantageous.

2. Genetic Drift

- Random changes in allele frequencies.

- Mainly affects small populations.

(Microevolution)

- Can result in the “founder effect.”-migration of a small subgroup of a population.

3. Gene Flow / Migration

- Genes moving in and out of a population.

– Immigration- individuals entering a population

– Emigration- ind. leaving a population

4. Non-Random Mating

- When organisms mate based on specific traits.

Ex: Height, Strength, Blue Eyes, Skin Color, etc.

5. Natural Selection

- The environment itself dictates the change in a population.

Three Types:

a. Stabilizing

- Selects the average traits in a population.

b. Directional

- Favors one extreme.

c. Disruptive

- Favors both extremes

Single Gene vs Polygenic Traits

• Single gene trait- controlled by a single gene with 2 alleles. – You either have it or you don’t.– Ex- widow’s peak, hitch hiker’s thumb

• Polygenic trait- controlled by 2 or more genes.– Ex- height, hair color

V. Pattern, Speed and Formation of SpeciesA. Patterns:

* These mainly occur within large populations (macroevolution).

1. Coevolution

- When two or more species evolve closely

together.

2. Convergent

- The environment selects which traits are beneficial.

- Dissimilar and/or similar species evolve similar traits.

3. Divergent

- When two or more related species become more and more dissimilar.

Two Types:

a. Adaptive Radiation

- When many species evolve from the same species.

Ex: Galapagos Finches

b. Artificial selection

- When an organism is bred for a specific trait(s).

Ex: Dogs from grey wolves

B. Formation of New Species (Speciation)

1. Reproductive Isolation- members of a population can no longer interbreed.

a) Geographical- When a population evolves into separate species due to a physical barrier.

b) Behavioral-

• have ability to interbreed but do not due to different courtship rituals.

–Ex- Eastern and Western Meadowlark

Reproductive Isolation Cont.

c) Temporal- – When species mate at different times. – Ex- 3 different orchids produce pollen on 3

different days.

C. Speed of Evolution

1. Gradualism

(Macroevolution = Large Populations)

- Speciation over very long periods of time.

- Usually millions of years.

2. Punctuated Evolution

(Microevolution = Small Populations)

- Speciation occurs quickly

- Can take only hundreds to thousands of years.