III. Darwin Presents His Case A. Publication of On the Origin of Species *Darwin studied his findings but didn’t publish them right away because they were so controversial. 1858 – Darwin receives essay from fellow naturalist Alfred Russel Wallace summarizing the same ideas as Darwin’s evolutionary theory. -Both men present their ideas together & in 1859 Darwin publishes his book, On the Origin of Species.

B. Inherited Variation & Artificial Selection *Darwin’s most important observation was that individuals within a species vary from each other. -Darwin learned that variation is heritable----We know specifically from our genes. -Breeders use variation to develop the best crops & animals. Darwin termed this artificial selection. Artificial selection – selection by humans for breeding of useful traits from the natural variation among different organisms.

C. Evolution by Natural Selection *Darwin compared artificial selection to nature & found that there was : 1. Struggle for existence – when members of each species compete regularly to obtain food, living space, & other necessities of life, ex : faster predators catch food & better protected/camouflaged prey survive. 2. Survival of the Fittest – when individuals that are better suited to their environment (have best adaptations) survive & reproduce most successfully.

C. Evolution by Natural Selection Fitness – ability of an individual to survive & reproduce in its specific environment. Adaptation – any inherited characteristic that increases an organism’s chance of survival. Successful adaptations allow organisms to become better suited to their environments, ex : can be anatomical or structural characteristics like sharp quills on a porcupine, physiological processes/functions, or behavior. -Darwin referred to survival of the fittest as natural selection because of its similarity to artificial selection.

C. Evolution by Natural Selection 3. Descent With Modification – principle that each living species has descended, with changes, from other species over time. -It implies that all living organisms are related to each other through common descent. Common descent – principle that states that all species, living & extinct, were derived from common ancestors.

D. Evidence of Evolution *Darwin believed that organisms had been evolving on Earth for millions of years. -His evidence for this process was in the fossil record, geographical distribution of living species, homologous structures of living organism, & similarities in early development, or embryology.

The Fossil Record 1. The Fossil Record – shows ancient life that was on Earth. By comparing older & newer rock fossils, scientists can see how life on Earth has changed over time. Fossil – preserved remains of ancient organisms. *Fossil record can’t be considered solid proof of evolution because it is incomplete, there are gaps in it.

Geographic Distribution of Living Things 2. Geographic Distribution of Living Things - Darwin found different species of animals living in similar environments throughout the world. -He realized that although different, many of these organisms had common features. -He concluded that similar ecological conditions & exposure to similar pressures of natural selection had caused development of similar

Homologous Body Structures 3. Homologous Body Structures – anatomical similarities among the body parts of animals. Homologous Structure – structures that have different mature forms in different organisms but develop from the same embryonic tissues, ex : when comparing arms/legs/wings/flippers, all vary in form/function but are constructed of the same basic bones.

Analogous Structures Analogous Structures – structures found in different types of organisms that are similar in function or outward appearance but dissimilar in basic structure or embryological development, ex : insect vs. bird wing.

Vestigial Organs Vestigial Organs – organs that serve no useful function in an organism, ex : human wisdom teeth & appendix.

E. Similarities in Embryology *Many animals have similar embryos. Embryology – the study of an organism before birth. -Similarities exist greatly between the embryos of vertebrates (animals with backbones), ex : human, fish, chicken. -Such similarities suggest common ancestry because the same groups of embryonic cells develop in the same order & in similar patterns to produce the tissues & organs of all vertebrates.

Extended tail-like vertebrae