What is evolution A gradual change in the

What is evolution? A gradual change in the genes of a population of organisms over time

What is meant by “last common ancestor? ” You Cousin Mom Aunt Grandparent Last common ancestor of you and your cousin

Evolution is a theory. What does this mean? • A theory in science is a well tested explanation of observable events supported by experimental evidence collected over time.

Charles Darwin’s Theory of Evolution • Individuals with the best adaptations for their environment survive and pass on their genes (natural selection) • All living species compete with each other for survival • All living things change over time • All species on earth (both alive and extinct) share a common heritage

Darwin’s Theory of Evolution by Natural Selection • Charles Darwin devised the • • theory of evolution by natural selection and published it in 1858 Natural Selection: organisms best adapted to their environment survive, reproduce, and pass on their traits Examples of natural selection Charles Darwin (1860 at age 51)

Bacterial Growth Antibiotic is present no antibiotic present Drug-resistant bacteria survive and reproduce Mutation makes bacteria resistant to drugs ANTIBIOTIC RESISTANCE

Evidence for Evolution • Fossil Record • Homologous and vestigial structures • Comparative embryology • Biochemical (DNA, RNA, proteins)

Fossil Record • Shows changes in a • • species over the course of time Older fossils are in bottom rock layers Radioisotope dating is used to determine the age of the rock the fossils are in Older fossils are in lower layers; younger fossils are in higher layers.

Homologous Structures • Structures with the same • design, but serve a different purpose (ex. Human arm, cat leg, flipper of a whale) Similarities in the structures suggest that the organisms shared a common ancestor. Four homologous structures. Note the similarity in the structure of each

Vestigial Structures A structure that is present in an organism but no longer serves its original purpose examples

Embryological similarities • Early embryos of many • • species look very similar The genes for early development of embryos are the same or similar for many species Suggests a common ancestor whom had these developmental genes Embryos of different vertebrate species

Biochemical Comparisons • Similarities in the genes and • • proteins of different species Closely related organisms share a high percentage of similarity in their DNA sequences Homeotic genes determine what structures develop where in an organism (ex. The placement and structure of the arms and legs)

Evolution of Populations Population Genetics Populations evolve, NOT individuals

Changes in the Gene Pool • Evolution is caused by changes • • in the gene pool of a population A gene pool is all of the genes in a population of a species The frequency of an allele in the gene pool is known as allelic frequency

What causes change in the Gene Pool? • Mutations • Natural Selection • Gene flow (movement of • genes into or out of the gene pool) Genetic drift (changes in allele frequency due to chance events) Gene flow between two populations

Speciation - the formation of a new species • Members of a population become • • • isolated from each other Each new population evolves through natural selection with no gene flow between populations Over time, the gene pool of each population changes due to natural selection and genetic drift When members from the two populations can no longer successfully reproduce with one another, they are said to be different species Speciation experiment with fruit flies (click picture for another example)

Isolating mechanisms that cause speciation • Geographic - a natural barrier prevent two groups from interbreeding • Temporal - different mating seasons prevent individuals from mating • Behavioral - different behaviors prevent interbreeding between populations * All of the above may lead to reproductive isolation (the two groups can no longer mate successfully) Geographic isolation by a barrier preventing gene flow between populations