Mechanism of Evolution

Beth Walker

Honors Biology

What is the mechanism for change over periods of time?

A. Jean Baptiste Lamarck – 18091. Organisms could acquire or lose certain traits

during their lifetime based on their use or disuse of a body part/organ.

2.

Lamarck Continued…

3. What are the problems with Lamarck’s hypotheses?

a. An organism cannot alter its body parts due to

effort alone.

b. Traits inherited in an organism’s lifetime are

not passed on to offspring through the sex

cells/gametes.

Lamarck – “Use and Disuse” Idea

Thomas Malthus – 1798

1. If the human population continues to grow, unchecked, eventually habitat, food, and water could limit human population growth.

2. Darwin read Malthus’s work and applied it to plants and animals.

Charles Darwin

1. First attended school to b/c a physician

2. Changes to b/c a clergyman3. Hired as the naturalist on the

ship, The Beagle, which sailed from 1831-1836

4. On the voyage, Darwin made copious notes and preserved

specimens of organisms never seen in England.

Charles Darwin Continued…

Charles Darwin Continued…

5. Observed patterns suggesting that species change over time and give rise to new species

6. Mockingbirds, finches, & tortoises were slightly different on every island in the Galapagos chain of islands.

7. Hypothesized the idea of natural selection in 1838, but did not publish due to the reactions of the religious community.

8. Jointly published his idea of Natural Selection (On the Origin of the Species) in 1859, along with Alfred Russell Wallace, which states:

Charles Darwin Continued …

Lead to the ideas of

Natural Selection &

Descent with

Modification

Natural Selection - Microevolution

a. There is a tendency for overpopulation

b. Organisms with beneficial traits live longer

and reproduce more.

c. The beneficial genes for the environment are

passed on to offspring during reproduction.• Camouflage – blending into environment

• Mimicry – copying the appearance of another

Descent with Modification - Speciation

a. Natural selection produces organisms

that have different structures or

occupy different habitats.

b. Over time, each new species is

descended, with changes, from other

species over time.

What is the raw material for natural selection?

A. Genetic Variation – differences in the DNA b/w organisms of the same species

B. What leads to genetic variation?1. Genetic Recombination

crossing over in Prophase I

of meiosis

2. Mutations random changes

in DNA; can be beneficial or

detrimental

Types of Natural Selection

A. Directional Selection individuals at

one end of a curve have a higher

fitness than other individuals.

Types of Natural Selection

B. Stabilizing Selection individuals near the center of the curve have the highest fitness.

Types of Natural Selection

C. Disruptive Selection individuals at both extremes of a curve have the higher fitness.

Types of Natural Selection