Mechanisms of Evolution EvA.1, EvA.2, EvC.12

What are some ways that evolution happens? 1. natural selection – organisms having traits that better enable them to adapt to specific environmental pressures will tend to survive and reproduce in greater numbers than others of their kind 2. genetic drift - describes random fluctuations in the number of variations of a gene in a population. Genetic drift takes place when the occurrence of variant forms of a gene, called alleles, increases and decreases by chance over time.

How does each account for the diversity of life? Natural selection – Predators, changes in climate, competition for food force organisms to change in order to survive. These forced changes allow for diversity among organisms. Genetic Drift – when alleles and genes change, organisms have different traits among them. This allows there to be diversity between similar organisms.

Natural Selection Natural selection forces organisms must adapt to the environment in different ways. 1. Structurally 2. Physiologically 3. Behaviorally

Structurally Gaining/losing body structure to aid in survival Ex. Giraffe’s long neck for eating leaves, webbed feet for swimming, thumbs for grasping, etc.

Physiologically Changing the normal functions of an organism. Ex. Regulating body temperature for environment (cold/warm blooded), female body changes due to pregnancy, sleep habits (hibernation).

Behaviorally Changing the way an organism behaves to survive in the environment conditions. Ex. Bird calls, migration patterns, mating rituals

Environmental change Changes in the environment can result in: Increasing the number of individuals in a species Species will survive and reproduce successfully. The emergence of new species over time New species develop due to the changes that have happened The extinction of some species Species will die out when they cannot survive in the environmental conditions

Video (13:10) http://media.hhmi.org/biointeractive/films/birth_death_genes.html