Theory of E v o l ut i o n Chapter 15

What is Evolution? Change over time The process by which modern organisms have descended from ancient organisms

2 Competing Theories: D arwin and L a m ar c k

Darwin and Lamarck agreed on a few things… Life is still changing Living things become better suited to their environment All organisms are related Simple  Complex

Lamarck Organisms can change the shape or size of organs depending on how they use them Acquired characteristics could be inherited. –If an animal altered its body during its lifetime, that change will pass to offspring Organisms have a tendency toward perfection

Darwin

Inherited Variation and Artificial Selection Artificial Selection: nature provides the variation and humans select those variations they find useful Darwin had no idea how heredity actually worked

Evolution by Natural Selection Darwin wanted to compare processes in nature to artificial selection –The struggle for existence –Survival of the fittest –Descent with modification

The Struggle for Existence High birth rates and shortage of basic needs would force organisms to compete Struggle for Existence: each species compete regularly to obtain food, living space, and other necessities of life.

Survival of the Fittest How well suited is an organism to its environment? Fitness: the ability of an individual to survive and reproduce in its specific environment Darwin proposed that fitness is a result of adaptations Individuals that are better suited to their environment survive and reproduce most successfully

Natural Selection Only certain individuals of a population reproduce In natural selection, traits being selected contribute to fitness in the environment Natural selection results in changes in inherited characteristics in a population

Lamarck - why was he wrong?? –Lamarck did not know how traits were inherited –He did not know that an organism’s behavior has no effect on the traits it passes down –Acquired characteristics are not passed on to offspring, –Organisms do not get what they "need" through "inner wants" or through "use and disuse” Individual intentions do not play a role. –Instead, the animals well suited survive and reproduce while those ill suited die