Essentials of BiologySylvia S. Mader

Chapter 14Lecture Outline

Prepared by: Dr. Stephen EbbsSouthern Illinois University Carbondale

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

14.1 Darwin’s Theory of Evolution

• Charles Darwin’s derived his theory of evolution in part from observations he made while serving as the naturalist aboard the HMS Beagle.

14.1 Darwin’s Theory of Evolution (cont.)

Before Darwin

• Prior to Darwin’s theories, there were different views of the world and living organisms.

Before Darwin (cont.)

Before Darwin (cont.)

• The research of several scientists helped change the world’s perception of the world and living organisms.

• Zoologist Georges Cuvier, who founded the field of paleontology, suggested that catastrophes were responsible for the drastic changes in living organisms over time.

Before Darwin (cont.)

Before Darwin (cont.)

• Jean-Baptiste de Lamarck offered explanations for the changes in organisms between strata.– Evolution occurred as the environment forced

organisms to adapt. – These adaptations caused less complex

organisms to evolve into more complex organisms.

– Adaptation occurs because of the use or disuse of a structure, an element of the theory of acquired characteristics.

Before Darwin (cont.)

• Darwin’s ideas were similar to those of Lamarck, but with important differences.– Darwin believed that living things share

common characteristics because they have a common ancestor.

– Darwin also believed that the organisms adapt to the environment, but through a process called natural selection.

Darwin’s Conclusions

• Darwin’s conclusions were based upon his study of geology, fossils, and biogeography.

Darwin’s Study of Geology and Fossils

• Geological theories contributed to Darwin’s efforts.

• James Hutton proposed that the Earth undergoes slow, continuous cycles of erosion and uplifting.

• Erosion deposits thick layers of sediment, which eventually form sedimentary rocks.

• The uplifting of sedimentary rock forms new land and can expose fossils.

Darwin’s Study of Geology and Fossils (cont.)

Darwin’s Study of Geology and Fossils (cont.)

Darwin’s Study of Geology and Fossils (cont.)

• Lyell proposed the theory of uniformitarianism, which maintained that extreme geological changes could be caused by slow, natural processes.

• This theory also suggested that the Earth must be very old, much older than most believed.

Darwin’s Study of Geology and Fossils (cont.)

• Darwin observed similar geological changes and collected fossils during his time on the Beagle.

• These activities caused Darwin to accept the fact that the Earth was very old.

• From this, Darwin proposed that modern organisms may have descended from now extinct organisms.

Darwin’s Study of Geology and Fossils (cont.)

Darwin’s Study of Biogeography

• Darwin made extensive comparisons between similar animals from around the world to understand evolution.

• He postulated that similar environments may have caused convergent evolution, or the development of similar adaptations.

Darwin’s Study of Biogeography (cont.)

Darwin’s Study of Biogeography (cont.)

• When Darwin’s ship reached the Galapagos Islands, he noticed that the finches had greatly diversified.

• The finches had different beak structures as well as different feeding habits.

Darwin’s Study of Biogeography (cont.)

Darwin’s Study of Biogeography (cont.)

• From his observation of the Galapagos finches, Darwin postulated that speciation had occurred.

• Speciation is the process by which different groups of an organism evolve independently from one another, ultimately becoming a different species.

Natural Selection and Adaptation

• Darwin suggested that natural selection was the process that caused adaptation.

• The process of natural selection has several preconditions that must be met.– The members of a population show variation.– More individuals are born in a population than die.– Some individuals inherit adaptive characteristics that

favor their survival and reproduction.

Natural Selection and Adaptation (cont.)

Natural Selection and Adaptation (cont.)

• If the preconditions are met, natural selection has consequences.– In each generation, an increasing number of

individuals have the adaptive characteristics.– Natural selection adapts a population to its

local environment.

• Natural selection relies on the variations produced by genetic changes.

Organisms Have Variations

• Prior to Darwin, variation within a population was ignored.

• Darwin argued that the random occurrence of these variations was essential to natural selection.

• These variations that allow for adaptation to the environment must also be heritable.

Organisms Struggle to Exist

• Thomas Malthus believed that death and famine were inevitable because human population increases faster than food supplies.

• Darwin used this concept to argue that available resources were insufficient to allow all members of a population to survive.

Organisms Struggle to Exist (cont.)

• Thus there is a constant struggle to obtain the resources needed to survive and reproduce.

Organisms Differ in Fitness

• Those organisms best capable of obtaining the resources necessary to survive and reproduce are those with the greatest fitness.

• The character that determines whether an organism is fit varies from population to population.

• When humans carry out artificial selection, breeders select specific traits that are favorable.

Organisms Differ in Fitness (cont.)

• The concepts of natural selection and fitness argue that interaction with the environment and random variation are responsible for evolution.

• This differs from the theory of acquired characteristics proposed by Lamarck.

Organisms Differ in Fitness (cont.)

Organisms Become Adapted

• The consequence of natural selection and fitness is that organisms adapt to their environment.

• The adaptations that make organisms more suited to the environment can occur simultaneously in different species.

• Convergent evolution occurs when different organisms acquire similar adaptations.

Organisms Become Adapted (cont.)

Evidence for Evolution

• According to the theory of evolution, organisms descend from a common ancestor but adapt to particular environments.

• There are several lines of evidence that support the theory of evolution.

Fossil Evidence

• The fossil record contains rich information about the life on Earth >10,000 years ago.

• One piece of evidence provided by the fossil record is that the pattern of evolution is typically from simple to more complex.

• The fossil record also reveals transitional links between different organismal groups.

Fossil Evidence (cont.)

Biogeographical Evidence

• Biogeography is the study of the distribution of plants and animals throughout the world.

• While there are many similar environments around the world, the plants and animals that live there are often unique.

• The different organisms must have arisen from different evolutionary events.

Biogeographical Evidence (cont.)

Anatomical Evidence

• Darwin and others have also showed that different species share vestigial structures that reveal their common descent.– Whales and snakes all show vestigial bones related to

four-legged animals.– Humans have a tailbone but not tail.

• Organisms may also have homologous structures, which are anatomically similar structures that reveal common ancestry.

Anatomical Evidence (cont.)

Anatomical Evidence (cont.)

• In contrast, organisms may have analogous structures, which have a similar function but are derived differently evolutionarily.

• The homology of all vertebrates can be seen in the similarities in embryonic development.

Anatomical Evidence (cont.)

Biochemical Evidence

• The study of biochemistry and genetics has shown that many organisms use similar chemicals and genes.

• The diversity in living organisms is due to slight differences in this set of genes.

Biochemical Evidence (cont.)