Theories of Evolution

Chapter 15 Part I

Definition of Evolution:• A heritable change in the

characteristics within a population from one generation to the next.

• “Change over time.”

• How does this happen?

Just So Stories

• How The Peacock Got its Tail

• Why Sex?

Ideas of Darwin’s Time (1800’s)

1. Curvier: studied rock strata and found that deeper rocks contained extinct life forms that became increasing different. Catastrophism- sudden geologic

catastrophes that caused mass extinctions in the past

2. Lyell: the geologic process that shaped the Earth’s surface still occur today Uniformitarianism

3. Jean Lamarck Life can arise from nonliving matter Simple life forms change over time

Inheritance of Acquired Characteristics: Organisms can acquire traits during their lifetime as a result of experience or behavior and can pass these traits on the future generations.

Examples:• Webbed foot = stretching of membrane

between toes• Long Necks = from stretching to get food

Darwin & Wallace’s Theory (1858)

• Theory of Natural Selection: Organisms best suited to their environment reproduce more successfully than other organisms.

• “Survival of the fittest”

Lamarck versus Darwin:

Charles Darwin• Voyage of the HMS Beagle• Published: On the Origin of Species by

Means of Natural Selection• Goals: present evidence that evolution

occurs and explain the variety and distribution of organisms

Darwin’s Observations:• 13 Similar but separate species of

finches– Different bill specialized for food source

• Overwhelming similarities lead to the belief of a common ancestor

Darwin’s Conclusions:1. All species are engaged in a

struggle to survive in their changing environment.

2. Species change through continual modifications.

3. Modifications that are best suited for the environment are preserved.

4. All species descended from one or a few original types of life (controversial!)

Modification by Natural Selection

• Mechanism by which evolution occurs

• Environment limits growth of populations– Overproduction: each species produces

more offspring than can survive to maturity

– Darwin used work of Thomas Malthus on human overpopulation to make conclusions about nature

• Genetic Variation: Not all individuals in a population are identical, thus the environment will affect individuals differently in a population

• Individuals with favorable traits will reproduce more often and in higher numbers than individuals with unfavorable traits.

Adaptation• An inherited trait that increases an

organism’s chance of survival in a particular environment

• “Adaptive Advantage”

Fitness:• a measurement of the ability of a

species to respond to the pressures of natural selection

• The ability of individuals to survive to propagate their genes

• “Survival of the Fittest”

Lamarck Reading 1. What is the role of the environment

in Lamarck’s explanation?2. What scientific approach is

suggested by Lamarck’s statement: “Nothing of all this can be considered as hypothesis or private opinion; on the contrary, they are truths which, in order to be made clear, only require attention and the observation of facts.”

Lamarck cont.3. Was Lamarck’s explanation

scientific? Why or why not?4. Can you propose any other

explanations for Lamarck’s observations about the disuse and use of organs?

Darwin Video• Who was Charles Darwin?