Natural Selection The mechanism that drives evolution of new species

The Environment presents challenges, or Certain individuals are better suited to overcome challenges based on their Well suited individuals are said to be “fit” to their environment These individuals live longer, reproduce often and pass their genes on Successful physical and behavioral traits are passed on

With your neighbor decide on a species of animal that you are familiar with. – What might a selective pressure be for individuals of that species? – What traits do individuals of this species have that help it specifically deal with that selective pressure?

Natural Selection in 5 Steps

1. Variation: Individual members of a species do not all look or act exactly alike. They have different traits that may allow them to be more successful in one environment or another. *Genetic mutations and sexual reproduction increase the variation in a population either by introducing new traits (mutations) or by mixing up the combinations of traits (sexual reproduction

2. Constant struggle: Some members of the species

3. Environment “selects” : Those that have traits that allow them to overcome the selective pressures survive and reproduce… *You may have heard the term, “survival of the fittest.” This isn’t entirely accurate. You don’t have to be the best of the best, you just have to squeak by *If you’re a horse outrunning a wolf, you don’t have to be faster than the wolf, just faster than the slowest horse that day

1. Population appears to adapt to the environment The successful traits keep getting passed down while unsuccessful ones

Types of Selection a.Directional: pushes the population towards one characteristic b.Distruptive: Pushes the population towards two opposite characteristics c.Stabalizing: Weeds out the most extreme characteristics

Speciation: Evolution of unique species Occurs when a population of the same species is isolated from each other and adapt to different environments and selective pressures As each population adapts to their different environments different traits are selected for Kaibab squirrel found in the North Rim of the Grand Canyon Aberts Squirrel found in the South Rim of the Grand Canyon

Change in behavior can also lead to speciation. – Example: Birds in a certain area are feeding during the day, but the competition is fierce, the limiting factor is the territory in which to feed. – Some birds are born with mutations that change their behavior to feeding at night. – The birds that feed at night don’t mate with the birds that are feeding during the day because they’re aren’t active at that time – Over time two distinct species arise, one that feeds during the day, one that feeds at night, even though they are not geographically isolated. *What traits might arise in a species of bird that starts feeding at night? Nighthawk

Why do mass extinctions lead to adaptive radiations? – Try to explain this in terms of natural selection