Bell ringer1. A species of mockingbird lives in the Apalachicola National

Forest. One year, a few of the mockingbirds were born with very long beaks. Over the next several years, the area experienced particularly cold winters. The weather forced the insects in the area to burrow deeper into the ground. Surveys of the mockingbird population showed that the number of long-beaked mockingbirds had increased. What would account for this increase in the number of long-beaked mockingbirds?

A. Short-beaked mockingbirds migrated to warmer climates.

B. Short-beaked mockingbirds became food for other animals.

C. Long-beaked mockingbirds were able to reach food and survived.

D. Long-beaked mockingbirds were able to stay warmer during the cold winters.

NATURAL SELECTIONSC.912.L.15.13 Describe the conditions required for natural selection, including: overproduction of offspring, inherited variation, and the struggle to survive, which result in differential reproductive success.

– Discuss mechanisms of evolutionary change other than natural selection such as genetic drift and gene flow

– Describe how mutation and genetic recombination increase genetic variation.

Essential Question: How

can a change in the

environment initiate a

change in a population?

NATURAL SELECTION

• WHAT YOU NEED TO KNOW

• You need to know the conditions required for natural selection to occur. These include: overproduction of offspring, inherited variation, and the struggle to survive, which result in differential reproductive success.

• You need to understand genetic drift and gene flow.

• You need to know how mutation and genetic recombination increase genetic variation.

NATURAL SELECTION:

• The process by which forms of life having traits that better enable them to adapt to specific environmental pressures, as predators, changes in climate, or competition for food or mates, will tend to survive and reproduce in greater numbers than others of their kind, thus ensuring the perpetuation of those favorable traits in succeeding generations.

• Sometimes called survival of the fittest.

• Individuals with favorable traits are more likely to leave more offspring better suited for their environment.

Natural Selection

CHARLES DARWIN

• Proposed Evolution Resulting from Natural Selection:

– Organisms Produce Many Offspring

– Competition for Food, Territory, Mates, etc.

– Those With Best Traits Survive

– Organisms Change Over Many Generations

• Time Frame: Millions of Years

OVERPRODUCTION OF OFFSPRING• Overproduction of offspring: In any given

generation, populations tend to create more progeny than can survive to reproductive age.

INHERITED VARIATION• Variations of genomes between members of

species, or between groups of species thriving in different parts of the world as a result of genetic mutation.

STRUGGLE TO SURVIVE

1. To remain alive or in existence.

2. To carry on despite hardships or trauma; persevere: families that were surviving in tents after the flood.

3. To remain functional or usable.

REASONS:

Not enough resources (food, water, shelter, mate, etc.)

DIFFERENTIAL REPRODUCTIVE SUCCESS• When one group has more viable offspring than

another. If two populations are similar but one has a variation that leads to fewer births and more deaths, you will see differential reproductive success between the populations.

GENETIC DRIFT

• Genetic drift is a mechanism of evolution that occurs by random chance rather than natural selection.

• In genetic drift, a population experiences a change in the frequency of a given allele, prompted by random luck rather than a need for adaptation.

• This differs from natural selection, in which allelic frequency is altered based on the fittest genes surviving to reproduce and the weaker genes dying off.

GENETIC DRIFTGenetic drift tends to be a phenomenon amongst smaller populations, while

natural selection holds sway in larger populations.

GENETIC DRIFT

GENE FLOW

• the alteration of the frequencies of alleles of particular genes in a population, resulting from interbreeding with organisms from another population having different frequencies.

GENE FLOW

GENE FLOW

GENETIC VARIATION

• Without genetic variation, some of the basic mechanisms of evolutionary change cannot operate.

• There are two sources of genetic variation, which we will learn more about:

GENETIC VARIATION

• Mutations are changes in the DNA. A single mutation can have a large effect, but in many cases, evolutionary change is based on the accumulation of many mutations.

• Genetic Recombination is the process of forming new allelic combination in offspring by exchanges between genetic materials (as exchange of DNA sequences between DNA molecules).

MUTATIONA permanent, heritable change in the nucleotide

sequence in a gene or a chromosome; the process in which such a change occurs in a gene or in a chromosome.

GENETIC RECOMBINATION

We Do

• Natural selection worksheet

Bell ringerA species of mockingbird lives in the Apalachicola National Forest. One year, a few of the mockingbirds were born with very long beaks. Over the next several years, the area experienced particularly cold winters. The weather forced the insects in the area to burrow deeper into the ground. Surveys of the mockingbird population showed that the number of long-beaked mockingbirds had increased. What would account for this increase in the number of long-beaked mockingbirds?

A. Short-beaked mockingbirds migrated to warmer climates.

B. Short-beaked mockingbirds became food for other animals.

C. Long-beaked mockingbirds were able to reach food and survived.

D. Long-beaked mockingbirds were able to stay warmer during the cold winters.

Bell ringerA species of mockingbird lives in the Apalachicola National Forest. One year, a few of the mockingbirds were born with very long beaks. Over the next several years, the area experienced particularly cold winters. The weather forced the insects in the area to burrow deeper into the ground. Surveys of the mockingbird population showed that the number of long-beaked mockingbirds had increased. What would account for this increase in the number of long-beaked mockingbirds?

A. Short-beaked mockingbirds migrated to warmer climates.

B. Short-beaked mockingbirds became food for other animals.

C. Long-beaked mockingbirds were able to reach food and survived.

D. Long-beaked mockingbirds were able to stay warmer during the cold winters.

A subspecies is a different group within a species that is able to interbreed but is usually prevented from doing so by geographical isolation. The Florida Panther is a subspecies of the American Cougar, and there are very few (less than 100) remaining in its population. When populations get this small, inbreeding results in low genetic diversity. The result is fewer beneficial adaptations that might help the animals survive environmental change, as well as an increase in the occurrence of genetic abnormalities. How can this subspecies of cougar be saved from extinction?

A. Keep the existing population in a controlled environment until their population increases.

B. Increase the genetic diversity by introducing other subspecies of cougar to the population.

C. Relocate remaining Florida Panthers to the larger populations of cougar subspecies in Texas and California.

D. Remove all the panthers with genetic abnormalities from the environment and leave only the healthy ones.

You Do

Florida Panthers are an endangered species. Because the remaining population of Florida Panthers is quite small and fairly closely related, there are concerns that there is not enough genetic variability within the population. How does greater genetic variability within the population affect the Florida Panthers' reproductive success?

A. It reduces the need to keep Florida Panthers alive in captivity.

B. It increases the rate of mutations that create helpful adaptations.

C. It reduces the expansion of harmful traits that result from inbreeding.

D. It increases the chance that the Florida Panther will be able to survive sea level rise.

Natural selection is a process that results in change within a species over time. Which of the following is NOT a condition required for natural selection to result in speciation?

A. overpopulation of the speciesB. genetic equilibrium of the speciesC. genetic variation within the speciesD. competition for survival within the species