Natural Selection and Darwin’s ideas Evolution Activity Start Pre-lab Objective: I can determine why natural selection is a key part of Evolution. Agenda: Natural Selection and Darwin’s ideas Evolution Activity Start Pre-lab

How would you define POPULATION? ___________________________________________________________________________

How do genetic variations occur? What is Evolution? Change in the genetic makeup of a population over time. Fitness – _________________________________________________________. Populations can evolve, not individuals. Diverse gene pool good for long-term survival of a species. ________________are important! How do genetic variations occur?

Where does Variation come from? Mutation random changes to DNA ____________________ environmental damage Sexual reproduction _________________ genetic recombination new arrangements of alleles in every offspring __________________________________

“The Origin of Species” Documented the occurrence of ____________. Suggested that the mechanism for evolution was ______________.

Observations: Observation 1 – ______________________________________________________________. .

Observation 2 Traits are inherited from _________________.

Observation 3 All species are capable of producing more _______________their environment can support.

Observation 4 Owing to lack of food or other resources, __________________________________.

Inference 1 Individuals _______________________ higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals.

Inference 2 This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations.

Nature Determines which characteristics are favorable. _______________________. Result - “Natural Selection”

Artificial Selection When man determines the characteristics that survive and reproduce. Result - the various breeds of animals and plants we’ve developed.

Evolution Success Measured By ______________ Whoever lives long enough and has kids is the “winner” in evolution.

Requirements In order for Natural Selection to work, you must have: _____________________. Long periods of time (according to Darwin).

Natural Selection 1. Populations are the units of Evolution. 2. __________________________________.

Comment Acquired characteristics may allow a species to evolve "outside" of Natural Selection. _______________

Essence of Darwin’s ideas Natural selection heritable variation exists in populations ______________________ more offspring than the environment can support _____________ for food, mates, nesting sites, escape predators differential survival successful traits = _____________ differential reproduction adaptations become more common in population

Lamarckian vs. Darwinian view in reaching higher vegetation giraffes stretch their necks & transmits the acquired longer neck to offspring Darwin giraffes born with longer necks survive better & leave more offspring who inherit their long necks 

DIRECTIONAL SELECTION STABILIZING SELECTION Effects of Selection DIRECTIONAL SELECTION STABILIZING SELECTION DISRUPTIVE SELECTION Changes in the average trait of a population giraffe neck horse size human birth weight rock pocket mice

In addition to natural selection, evolutionary change is also driven by random processes…

II. GENETIC DRIFT The smaller the population, the less genetic variety it has. In a very small population, alleles can be lost from one generation to the next, simply by random chance. When a population evolves only because of this type of random sampling error, _____________is taking place.

Genetic Drift Chance events changing frequency of traits in a population not adaptation to environmental conditions not selection ____________ small group splinters off & starts a new colony it’s random who joins the group ___________ a disaster reduces population to small number & then population recovers & expands again but from a limited gene pool who survives disaster may be random Founders: When a new population is started by only a small group of individuals. Just by chance some rare alleles may be at high frequency; others may be missing; skew the gene pool of new population. Ex: human populations that started from small group of colonists example: colonization of New World Bottleneck: When large population is drastically reduced by a disaster-famine, natural disaster, loss of habitat…loss of variation by chance event alleles lost from gene pool not due to fitness, narrows the gene pool

FOUNDER EFFECT

BOTTLENECK EFFECT

Ex: Cheetahs All cheetahs share a small number of alleles less than 1% diversity 2 bottlenecks 10,000 years ago Ice Age last 100 years poaching & loss of habitat

Conservation issues Peregrine Falcon Bottlenecking is an important concept in conservation biology of endangered species loss of alleles from gene pool __________________ Breeding programs must consciously outcross Golden Lion Tamarin

Human Impact on variation How do we affect variation in other populations? Artificial selection/Inbreeding Animal breeds ___________________ Insecticide usage resistant bacterial strains