Natural Variation & Artificial Selection

Natural Variation & Artifical Selection Darwin, through many observations, explained evolution by natural variation In 1859, Darwin published “On the Origin of Species” where he proposed his theory of evolution Natural variation – differences among individuals of a species and is found in all types of organisms (inherited traits) Breeders routinely used variations to improve crops and livestock = selective breeding aka artificial selection Artificial selection – nature provided the variation among different organisms, and humans selected those variations they found useful –Ex. Only cows that produce the most milk are bred

Evolution by Natural Selection Struggle for existence – members of each species compete regularly to obtain food, living space, and other necessities

Evolution by Natural Selection (continued) Survival of the fittest – how well suited an organism is to its environment –Fitness – ability of an individual to survive and reproduce in its specific environment –Adaptation – leads to fitness – any inherited characteristic that increases an organism’s chance of survival – can be physical or behavioral adaptations

Survival of the Fittest (continued) Generation after generation, individuals compete to survive and produce offspring Individuals with characteristics that are NOT well suited to their environment die or leave few offspring Individuals with characteristics that ARE well suited to their environment survive and reproduce most successfully

Natural Selection Takes place without human control or direction Over time, natural selection results in changes in the inherited characteristics of a population

Natural Selection Chromosome with gene conferring resistance to pesticide Reproduction Survivors Insecticide application

Descent with Modification Over long periods of time, natural selection produces organisms that have different structures or occupy different habitats. As a result, species today look different from their ancestors. All living organisms are related to one another through common ancestors = common descent