Evidence that supports the theory of Evolution Fossil Records Geographic Distribution Ebryology Homologous Structures Vestigial Structures Biochemistry Artificial Selection

What Is Evolution?

The central idea of evolution is that life has a history. The living things on Earth have changed over time, and that the different species on Earth today share common ancestors.

Over a great period of time evolution can result in SPECIATION Speciation - The formation of a new species The Tree of Life

Extinction Millions of organisms that lived in the past have gone extinct. We know of their existence from fossils or rarely from frozen specimens.

Related Species There are many organisms that are different species, but are obviously very closely related. It is very apparent that the American cougar and the African lion are related. They both share a common ancestor from the past.

Related Species All of the many cat species are related. They have very similar anatomy and DNA. Cats share a common ancestor that lived in the past. Not all cat species that evolved are alive today.

Related Species The saber- toothed cat became extinct about 10,000 years ago It has the same basic skeleton as other cats. The most distinguishing feature of this cat is its long canine teeth.

Related Species All cats have the same basic skeleton.. There are some modification of this skeleton in the various cat species. The bobcat has a short tail. The saber-toothed cat has huge fangs Evolution works by taking an existing structure (such as the basic cat skeleton) and modifying that structure.

Evolution is possible because of…. Genetic Variation

Why Genetic Variation? If a population was 100% the same… the processes that cause evolution would have NO effect because the genetic make-up would never change.

tutorials/flash/life4e_15-6-OSU.swfhttp://zoology.okstate.edu/zoo_lrc/biol1114/ tutorials/flash/life4e_15-6-OSU.swf

Evolution only occurs when there is a change in gene frequency within a population over time. 1 st generation of Beetle population Many generations later of the same population

The Gene Pool Gene frequency refers to how frequent a gene or allele is in a population. The white allele has a frequency of 43% in the mouse population illustrated here. 13 of the 30 alleles are white. A change in the gene frequency of a population results in small evolutionary changes or microevolution.

Changes in Gene Frequency The population on the top has 13 white alleles and 17 black alleles. Some of the mice have died. The population now has 7 white alleles and 17 black alleles. Gene frequency has changed. The population is evolving.

What causes these changes? There are 5 main mechanisms for evolutionary changes:

5 Agents of evolutionary change MutationGene Flow Genetic DriftSelection Non-random mating

Mutation A change in a DNA sequence, usually occurring because of errors in replication or repair. Mutation is the ultimate source of genetic variation. Fruit Fly Example

Mutations produce the genetic variation needed for evolution.

Gene Flow Either by immigration or emigration (individuals move to another population and shares their genes there).

1 st generation of Beetle population Many generations later of the same population

Gene flow moves alleles from one population to another.

Genetic Drift The change of allele frequencies in a population over time due to random events forming successive generations.

Genetic Drift A random change in allele frequency

Genetic Drift These individuals may carry alleles in different relative frequencies than did the larger population from which they came If so, the population that they found will be genetically different from the parent population This cause is not natural selection, but chance

For example: Green beetles reduce in numbers because an external factor has caused them to produce less offspring causing a more dominant brown population.

Genetic drift changes allele frequencies due to chance alone.

Natural Selection A process of evolution in which traits that result in better fitness of an individual survives to the next generation.

Natural selection selects for traits advantageous for survival.

The beaks of these finches adapted to what type of food they ate. These traits carried on from generation to generation because the trait became favorable for the environment they lived in.

Sexual Reproduction- brings together a new combination of genes. Introduces new combinations of genes every generation.

Sexual selection selects for traits that improve mating success.

Hardy-Weinberg equilibrium describes populations that are not evolving. Genotype frequencies stay the same and evolution stops if five conditions are met. –No genetic drift; very large population –No emigration or immigration: no gene flow –No mutations: no new alleles added to gene pool –No sexual selection: random mating occurs –No natural selection: all traits aid equally in survival

In nature, populations are expected to evolve because a population can’t maintain equilibrium forever. –Population numbers will always be threatened by different factors –Individual organisms will continue to migrate –New genetic mutations occur frequently –Species select mates; random mating rarely occurs –The environment has changed on Earth and continues to change

Evolution at work Although evolution cannot be seen on the small scale of time, the works of evolution are occurring all the time in populations. These processes are what contribute to the evolutionary changes between all species.

"One obstacle to understanding evolution is the common misconception that individual organisms evolve. It is the population, not its individuals, that evolves, as some heritable variation becomes more common at the expense of others."

Reviewing the Mechanisms of Evolution

Mutations New Population A new allele is formed because of a change in DNA.

Gene Flow New Population Alleles increase because of immigration or decrease because of emigration.

Genetic Drift New Population A chance event causes a drastic change in the population

Natural selection New Population A particular trait helps an organism better survive in the environment.

Sexual Selection New Population A particular trait increases the chance that an organism will mate.