Natural and Artificial Selection

Learning Objectives Be able to explain the 4 factors in Natural Selection Be able to differentiate between Natural Selection and Artificial Selection

Natural selection and Evolution Natural selection will lead to evolution when individuals with certain characteristics have a greater survival or reproductive rate than other individuals in a population Natural selection = Process by which traits become more or less common in a population

Natural Selection is… …..the logical result of four features of living systems (VIST) Variation - individuals in a population vary from one another Inheritance - parents pass on their traits to their offspring genetically (overproduction) Selection - some variants reproduce more than others (Survival of the fittest, competition, overproduction) Time - successful variations accumulate over many generations

V is for…..Variation Organisms within a population exhibit individual variation in appearance and behaviour Could be seen as “mutations” Ex: body size, hair color, voice properties Ex: webbed feet

I is for….Inheritance (of successful variations) Organisms that survive and reproduce have the chance to pass their traits to the next generation The picture on the right illustrates the crows eating the green beetles and not the brown ones. Over time, the brown beetles will be the ones to survive and reproduce passing on their traits to the next generation Individuals in populations vary slightly from one another. Individuals with those slightly advantageous variations will produce more offspring than others. Those offspring, in turn, inherit the successful variations and produce more offspring themselves. As generations pass, the population evolves towards the variation that is the more successful.

I is for….Inheritence Species produce far more eggs/seeds than could be supported by ecosystem Necessary to ensure there would be enough adults to continue the species Ex: female horseshoe crab lays 100, 000 eggs during breeding season Only 1 in 130, 000 eggs survives to adulthood Many eggs lost to predators before hatching Darwin observed that many species produce far more eggs or seeds than could every develop into adults and be supported by the ecosystem

S is for….Selection In order to have their traits passed down, organisms have to struggle to survive Struggle for Existence (competition) Members of same species compete for food, water, shelter, space and mates Those best suited for survival/competition had advantage Ex: long and short neck turtles competing for food Ex: feather train on male peacocks to attract mate Turtle example: during times of adequate rainfall, vegetation was available for both types of tortoises. However, in dry conditions, tortoises with long necks were favored for survival since they could reach leaves that were higher off the ground. Long neck turtles best suited for survival

S is for….Selection cont’d “Survival of the fittest” How well suited an organism is to its environment Fitness: ability of an individual to survive and reproduce in its environment Adaptation: inherited characteristic that increases an organism’s chance of survival Fitness is the result of adaptation ex: prey with some defense mechanism is more “fit” than prey without a defense mechanism

http://www.youtube.com/watch?v=zbe27IXusWQ&list=PLAB1390BAE600B259

T is for…. Time Overtime, the successful variations will accumulate

Artificial Selection When humans choose traits and breed organisms for that trait Also known as selective breeding Ex: dogs, plants

Natural Selection vs. Artificial Selection Dominated by environmental factors Where nature chooses organism with best traits for survival Ex: tigers developed stripes to sneak up on prey Artificial Selection Controlled by humans, “goal-directed” Person chooses which traits of the organism they want it to have Ex: dogs Both natural selection and artificial selection rely on principles of inheritance for maintain favorable traits from one generation to the next and both produce the same outcome: change over time.

http://learn.genetics.utah.edu/content/variation/artificial/

Example… African elephants typically have large tusks. The ivory in the tusks is highly valued by some people, so hunters have hunted and killed elephants to tear out their tusks and sell them (usually illegally) for decades. Some African elephants have a rare trait -- they never develop tusks at all. In 1930, about 1 percent of all elephants had no tusks. The ivory hunters didn't bother killing them because there was no ivory to recover. Meanwhile, elephants with tusks were killed off by the hundreds, many of them before they ever had a chance to reproduce. The alleles for "no tusks" were passed along over just a few generations. The result: As many as 38 percent of the elephants in some modern populations have no tusks Would you say this is a case of Natural Selection or Artificial Selection and why?

The bollworm is a pest that eats and damages cotton crops Some cotton crops have been genetically modified to produce a toxin that's harmful to most bollworms. A small number of bollworms had a mutation that gave them immunity to the toxin. They ate the cotton and lived, while all non-immune bollworms died. The intense population pressure has produced broad immunity to the toxin in the entire species within the span of just a few years Describe what the 4 factors of natural selection are in this example

How is artificial selection dependent on variation in nature?