Evolution Glencoe Chapter 15

Darwin’s Theory of Natural Selection Charles Darwin

Darwin’s Theory of Natural Selection HMS Beagle

Darwin’s Theory of Natural Selection Galapagos Islands Each island had different variety of animals Finches on islands resembled animals on South American mainland but were not the same species Darwin suspected that populations from mainland changed after reaching the islands Hypothesis: new species occur through small changes in ancestral species

Darwin’s Theory of Natural Selection Artificial selection-changes in species due to human intervention, breeding to produce desirable traits Darwin-four basic principles Individuals in a population show variation Variations can be inherited, passed down from parent to offspring Organisms have more offspring than can survive on available resources Variations that increase reproductive success will have a greater chance of being passed on than those that do not increase reproductive success Natural selection

Darwin’s Theory of Natural Selection Principles of natural selection Principle Example Individuals in a population show variations among others of the same species. The students in a classroom all look different. Variations are inherited. You look similar to your parents. Animals have more young that can survive on the available resources. The average cardinal lays nine eggs per summer. If each cardinal lived only one year, in seven years there would be a million offspring if all survived. Variations that increase reproductive success will be more common in the next generation. If having a fan-shaped tail increases reproductive success of pigeons, then more pigeons in the next generation will have fan-shaped tails.

Darwin’s Theory of Natural Selection Darwin-The Origin of Species Evolution: cumulative changes in groups of organisms through time

Evidence of Evolution Fossils-provide record of species that lived long ago Derived trait-newly evolved features feathers Ancestral trait-more primitive features that do appear in ancestral forms Teeth

Evidence of Evolution Comparative anatomy Homologous structures-anatomically similar structures inherited from a common ancestor

Evidence for Evolution Vestigial structures-reduced forms of functional structures in other organisms Human appendix, snake pelvis

Evidence for Evolution Analogous structure-used for the same purpose and superficially similar in construction, but not inherited from a common ancestor

Evidence for Evolution Comparative embryology Embryo: early, pre-birth stage of an organism’s development Vertebrate embryos exhibit homologous structures during certain phases of development but become totally different structures in the adult forms

Evidence for Evolution Comparative biochemistry-comparing molecules and amino acid sequences of different organisms Geographic distribution Biogeography-study of distribution of plants and animals around the world

Evidence for Evolution Adaptation-trait shaped by natural selection that increases an organism’s reproductive success Fitness-measure of contribution a trait makes to next generation Ability to survive and reproduce Camouflage, mimicry

Shaping Evolutionary Theory Population genetics Hardy-Weinberg principle=when allelic frequencies remain constant, a population is in genetic equilibrium Conditions Large population No immigration or emigration Random mating No mutations No natural selection

Shaping Evolutionary Theory Genetic drift-any change in allelic frequencies in a population due to chance Founder effect-small sample of population settles in location separated from the rest of the population Bottleneck-population declines to very low number then rebounds

Shaping Evolutionary Theory Modes of selection stabilizing- favors intermediate phenotypes Directional selection-favors an extreme Disruptive selection-favors both extremes over intermediate

Shaping Evolutionary Theory Sexual selection Males and females differ in appearance Preference by one sex of individuals of the other

Shaping Evolutionary Theory Reproductive Isolation Prezygotic isolating mechanisms Geographical, ecological, behavioral Postzygotic isolating mechanisms Fertilization occurs but offspring cannot develop or reproduce

Shaping Evolutionary Theory Speciation-the formation of a new and distinct species Allopatric speciation-physical barrier divides one population into two or more populations Sympatric speciation-species evolves into another without a physical barrier

Shaping Evolutionary Theory Patterns of Evolution Adaptive radiation-one species gives rise to many species in response to new habitat or other factors Coevolution-evolving in close relationship with other species Plant and insect relationship Plant evolves chemical defense against insects, insects evolve resistance

Shaping Evolutionary Theory Convergent evolution-unrelated species evolving similar traits

Shaping Evolutionary Theory Theories of rate of speciation Punctuated equilibrium-rapid spurts of genetic change Gradualism-evolution proceeds in small steps