Chapter 2

The Development of Evolutionary Theory

Chapter Outline Brief History of Evolutionary Thought Natural Selection in Action Constraints on Nineteenth-Century

Evolutionary Theory Opposition to Evolution

Evolution A change in the genetic structure of a

population. Also refers to the appearance of a new

species. Often controversial, some religious views

hold that evolutionary statements run counter to biblical teachings.

Evolution Is a Theory The theory has been supported by a

mounting body of genetic evidence. The theory has stood the test of time. The theory stands today as the most

fundamental unifying force in biological science.

Pre-scientific View In the middle ages, the predominant world was

stasis, the world was fixed and unchanging. The great chain of being held that life was

arranged from simplest to most complex. It was believed that the earth was “full” and

nothing new could be added. The world was seen as the result of a grand

design - God’s design.

The Scientific Revolution Discovery of the new world challenged

fundamental views about the planet. Exposure to new plants and animals

increased awareness of biological diversity.

The Scientific Revolution Copernicus challenged the idea that the

earth was the center of the universe. Galileo’s work supported the idea that

the universe was a place of motion. Keppler, Descartes and Newton

established the laws of physics, motion and gravity.

Precursors to the Theory of Evolution John Ray provided first definition of the

concept of species and genus. Carolus Linnaeus developed system of

classification and the basis for taxonomy. Comte de Buffon stressed the

importance of change in the universe and the environment as an agent of change.

Precursors to the Theory of Evolution John Baptiste Lamack was the first scientist to

produce an explanation for the evolutionary process.

Georges Cuvier introduced the concept of extinction and the theory of catastrophism.

Charles Lyell developed the theory of uniformitarianism.

Thomas Malthus wrote about relationship between food supply and population increase.

Charles Darwin (1809-1882) Ideas were formed while serving as a naturalist

on the voyage of the HMS beagle. Darwin saw the importance of biological

variation within a species. Recognized the importance of sexual

reproduction in increasing variation. By 1844, Darwin had complete the work that he

would publish fifteen years later.

The Path of the HMS Beagle

Alfred Russell Wallace(1823-1913) A naturalist who worked in South America

and Southeast Asia. Suggested species descended from other

species and new species were influenced by environmental factors.

Presented paper on evolution and natural selection to the Linnean Society of London jointly with Darwin.

Contrasting Views on Evolution

Contrasting Views on Evolution

Processes of Natural Selection

1. Species can produce offspring at a faster rate than food supplies increase.

2. There is biological variation within all species.

3. In each generation, more individuals are produced than can survive.

Processes of Natural Selection

4. Individuals that possess favorable traits or variations are more likely to survive and produce offspring.

5. Environmental context determines whether a trait is beneficial.

6. Traits are inherited and passed on to the next generation.

Processes of Natural Selection

7. Variations accumulate over long periods of time, so later generations may be distinct from ancestral ones.

8. As populations respond to pressures over time, they may become distinct species, descended from a common ancestor.

Evolutionary Change Through Natural Selection1. A trait must be inherited if natural selection is

to act on it.2. Natural selection can’t occur without

population variation in inherited characteristics.

3. Fitness is a relative measure that changes as the environment changes.

4. Natural selection can only act on traits that affect reproduction.

Quick Quiz

1. To understand the complexities of evolution one must be well versed in

a) mathematics and statistics.

b) botany and paleontology.

c) genetics and biology.

d) anatomy and physiology.

Answer: c To understand the complexities of

evolution one must be well versed in genetics and biology.

2. Genetic evidence supports evolution.

a) True

b) False

Answer: true Genetic evidence supports evolution

3. Darwin realized that variation among _________________ was how selection occurred, ultimately causing change in species.

Answer: individuals• Darwin realized that variation among

individuals was how selection occurred, ultimately causing change in species

5. Natural selection acts on existing _________________ within a species.

Answer: variation Natural selection acts on existing

variation within a species.