Darwin Presents His Case (Ch 16.3) Unit 4

Evolution by Natural Selection The Origin of Species by Charles Darwin Darwin took his own ideas combined with Malthus and Lamarck to produce a theory regarding evolution Struggle for Existence Malthus → the more individuals that are produced than can survive will need to compete for food, living space, and other limited necessities of life Variation and Adaptation Variations play a vital role in the ability for organisms to survive Adaptation: any heritable characteristic that increases an organism’s ability to survive and reproduce in its environment Structural Adaptation: changing the appearance to survive Physiological adaptation: internal systemic responses Behavioral adaptation: acting a certain way to survive

Types of Adaptation Camouflage Mimicry ` Behavioral

Evolution by Natural Selection Survival of the Fittest Lamarck → connection between the way an organism makes a living and the environment in which it lives Fitness: describes how well an organism can survive and and reproduce in its environment Highly adapted to environment and reproduces = high fitness Low adaptations and little to no offspring = low fitness Survival of the Fittest: the differences in rates of survival and reproduction Survival = reproducing and passing on adaptations to offspring

Natural Selection Natural Selection: organisms with variations most suited to their ecological environment survive and leave more offspring (environment influences fitness) Natural Selections Occurs When: More individuals are born than can survive (struggle for existence) There is natural heritable variation (adaptation) There is variable fitness among individuals (survival of the fittest) Generation to generation, populations will continue to change until they become adapted to their environment Natural selection does not make “perfect” organisms; it just makes organisms that can survive and reproduce in their living environment → If the environment changes, the species needs to adapt or runs the risk of becoming extinct

Natural Selection v. Artificial Selection Artificial Selection (selective breeding) Intentional reproduction of individuals that have desired traits Breeding certain organisms to get the desired traits Only certain individuals will produce offspring Natural Selection Organisms variations are best suited to their ENVIRONMENT Organisms will adapt to their environment and the adaptive changes will be passed from parent to offspring Only certain individuals will produce offspring

Common Descent Parent + Parent = Offspring 1 → Offspring 1 + Offspring 1 = Offspring 2 → and so on… Well adapted species will survive and reproduce in order to survive over time Descent with Modification: species descend from a common ancestor but modify over time are modified in order to continue to survive through the generations Lyell and Hutton → Deep time gave enough time for natural selection to act on the species Darwin used the fossil record to prove descent with modification Darwin created one of the first cladograms showing how species evolved from a common ancestor Principle of Common Descent: all species -- living and extinct -- are descended from ancient common ancestors