Evolution Part II Principles of Life Science Rainier

Evolution Part II Principles of Life Science Rainier Jr/Sr High School Mr. Taylor

Evolution n Remember: – Evolution means “change over time” – Natural selection is a process. n Those organisms with the greatest number of beneficial adaptations in an environment will survive longer and be able to reproduce in greater numbers. Their offspring will have those beneficial adaptations in greater numbers over time.

Homologous vs Analogous n When scientists talk about similar structures on different organisms, those similarities fall into two categories: 1. Homolgous structures: structures that may not look like one another externally but share a common internal structure. It is thought that this indicates a common ancestry. Examples include human arms and birds’ wings – Vestigial structures: structures much reduced in size and function; thought to indicate common ancestry. An example is the snake’s pelvis.

Homologous vs Analogous n When scientists talk about similar structures on different organisms, those similarities fall into two categories: 2. Analogous structures: structures that have similar external appearance but do NOT share a common internal structure. The structures do NOT indicate common ancestry but adaptation to a common environment. Examples include an insect and a bird wing.

Types of Natural Selection n Natural selection causes changes in one of three patterns: 1. Stabilizing selection: the high and low values are selected against and the “middle” value becomes more common. The population’s curve shifts toward the middle values.

Types of Natural Selection n Natural selection causes changes in one of three patterns: 2. Directional selection: selection causes the population’s average curve to move only toward either the high or low value.

Types of Natural Selection n Natural selection causes changes in one of three patterns: 3. Disruptive selection: the high and low values are favorably selected. The population’s curve moves away from the middle.

QUIZ!!! n Give a possible example for – Disruptive selection – Directional selection – Stabilizing selection

Divergent vs Convergent n Divergent Evolution: – Divergent means “to go apart” – Results when disruptive selection causes two or more different species develop from a common ancestor. – These species have homologous structures: the more closely related, the more homologous features they share.

Divergent vs Convergent n Convergent Evolution: – Convergent means “to come together” – In convergent evolution, the two species are not closely related but do resemble each other because they share a common environment. – These species share a number of analgous features because they share common needs.

What keeps things from evolving? (What creates a stable population? ) 1. Large population size: keeps random events from affecting gene frequency. 2. No mutations: keeps new genes from entering the population 3. Closed population: the only changes to the population are births and deaths. 4. Totally random mating: mating selections are not based on any traits 5. All traits give equal chance of survival: there are no “lethal” traits

Ontogeny recapitulates phylogeny Ontogeny = the development of the embryo n Recapitulates = retells n Phylogeny = the history of an organism’s evolution. n

That’s All Folks!!!