organisms produce more offspring than the environment can support DARWIN’S THEORY AND THE MODERN SYNTHESIS Darwin, an English naturalist, proposed natural selection as the mechanism of evolution Darwin observed that organisms produce more offspring than the environment can support organisms vary in many characteristics these variations can be inherited

Darwin concluded that individuals best suited for a particular environment are more likely to survive and reproduce than those less well adapted Darwin saw natural selection as the basic mechanism of evolution As a result, the proportion of individuals with favorable characteristics increases Populations gradually change in response to the environment

This is called artificial selection Darwin also saw that when humans choose organisms with specific characteristics as breeding stock, they are performing the role of the environment This is called artificial selection Example of artificial selection in plants: five vegetables derived from wild mustard Figure 13.4A

Example of artificial selection in animals: dog breeding English springer spaniel German shepherd Yorkshire terrier Mini-dachshund Golden retriever Hundreds to thousands of years of breeding (artificial selection) Ancestral dog Figure 13.4B

Thousands to millions of years of natural selection These five canine species evolved from a single common ancestor species through natural selection African wild dog Coyote Fox Wolf Jackal Thousands to millions of years of natural selection Ancestral canine Figure 13.4C

Important terminology Variation – Having genotypic and phenotypic differences in any population Heritable – Any genetics that can be passed on to future generations Fitness – Success of an organism’s individual adaptations and natural selection – usually measured by ability to reproduce. Adaptation –traits that make an organism to thrive and reproduce in its environment.

4 parts of Natural Selection

Scientists can observe natural selection in action Evolutionary adaptations have been observed in populations of birds, insects, and many other organisms Example: camouflage adaptations of mantids that live in different environments Figure 13.5A

Insecticide application The evolution of insecticide resistance is an example of natural selection in action Insecticide application Chromosome with gene conferring resistance to insecticide Additional applications of the same insecticide will be less effective, and the frequency of resistant insects in the population will grow Survivor Figure 13.5B

Sometimes, natural viruses or bacteria attack a population, killing those that have susceptibility to disease, leaving only that that are resistant to survive and reproduce.

Populations are the units of evolution A species is a group of populations whose individuals can interbreed and produce fertile offspring Human populations tend to concentrate locally, as this satellite photograph of North America shows The modern synthesis connects Darwin’s theory of natural selection with population genetics Figure 13.6

Adaptive change results when natural selection upsets genetic equilibrium Natural selection results in the accumulation of traits that adapt a population to its environment If the environment should change, natural selection would favor traits adapted to the new conditions Because of this, it is populations, NOT individuals, that are theorized to evolve or change over time. Today, evolution is a term used to describe biological change over time.