Evolution:Why Are There So Many

Living Things?

Where Did the Idea of Evolution Come From?

• Middle Ages:– “Ladder of Life”

• Complex organisms found at highest rungs

• Less complex at lower rungs

• 1800’s– Georges Cuvier

brought study of fossils to the level of science.

Where Did the Idea of Evolution Come From?

• Charles Lyell– Proposed theory of uniformitarianism.

• Jean-Baptiste Lamarck– Published theory of the inheritance of

acquired characteristics.

Charles Darwin

• Loved nature• Studied medicine

– Struggled with the inhumane operating procedures

• Switched to religion• Offered position as

naturalist on British survey ship, The Beagle.

Voyage around the World• Studied animals and

fauna. • Noticed South

American fossils differed from contemporaries.

• Collected data for 27 years to support his mechanism for evolution.

Fathers of Evolution

• Alfred Wallace studied in Brazil and East Indies.

• Developed mechanism of evolution independently of Darwin.

• Sent a copy of it to Darwin. – Contained same conclusions as Darwin

• Both presented their data at Linnaean Society of London in July 1858.

How Did Darwin Account for Species?

• In Origin of Species, he developed two main concepts– Evidence that

evolutions has occurred.

– Mechanism for evolution :natural selection.

Major points of Darwin’s theories of evolution and natural selection

• First observation:– Populations have

the potential to increase exponentially.

• Based on thoughts by Thomas Malthus

Major points of Darwin’s theories of evolution and natural selection

• Second observation:– Populations are fairly

constant in size.

Major points of Darwin’s theories of evolution and natural selection

• Third observation:– Natural resources are limited.

• Limited amount of space, nutrients, shelter

• Results in competition for resources to survive.

Major points of Darwin’s theories of evolution and natural selection

• Deduction one:– Only some organisms

survive. There is a struggle for existence among individuals in a population.

• Organisms posses characteristics that enhance survival– Called adaptations.

Three Types of Adaptations

• Morphological-anatomical: modifications in form and structure that enhance survival.

• Biochemical-physiological: modifications in the production and use of chemicals by organisms.

• Behavioral Adaptations: Modifications in animal interactions with others and environment.

Major points of Darwin’s theories of evolution and natural selection

• Fourth observation:– There is variation within individuals of a population

and variations are inherited.

Major points of Darwin’s theories of evolution and natural selection

• Deduction two:– Individuals with

favorable variations are more likely to survive and reproduce.

• Natural Selection:– “preservation of

favorable variations and the rejection of injurious variations”

Major points of Darwin’s theories of evolution and natural selection

• Deduction three:– Accumulation of

inheritable variation over many generations is evolution.

• If changes within a species become great enough, a new species can result.

What is a species?

• Species are considered extinct if they do not interbreed in nature.– Implies offspring must also be able to reproduce.

Evidence supporting Theory of Evolution

• Selective breeding practices used by farmers result in:– “improved”

domesticated plants and animals.

• Darwin wondered if nature could do the same.

Evidence supporting theory of evolution

• Fossil record– Comparing fossils from ancestors with today’s

species demonstrates species have evolved.

Evidence supporting theory of evolution

• Homologous structures– Structures dissimilar in

form and function. • but share underlying

structural similarities

– Similarity due to a common ancestor?