WHAT CAUSES EVOLUTION TO OCCUR? DARWIN’S MECHANISM: THE THEORY OF NATURAL SELECTION

NATURAL SELECTION DEFINITION: What causes natural selection? the process by which organisms that are better suited to an environment survive and reproduce in greater number than those less suited. What causes natural selection? Environmental Change “Survival of the Fittest” (But what is fit????) Categorized into 5 Steps

STEP 1: Overproduction All species over reproduce creating a population with many variations (alleles) the total of all alleles (or variations) in the population is called a gene pool What is the allele frequency for feather color in this population of birds?

STEP 2: Inherited Variation Variations within a population come from mutations & random mating changing the populations gene pool. MUTATIONS: Changes in an organisms DNA or genes (Darwin was missing this key info on genetics) RANDOM MATING: mixing of genes through reproduction A change in the gene for feather color creates different alleles which creates different coloration of bird feathers in the population VARIATIONS IN BIRD COLOR: Most birds are born with traits (genes) for being blue-green in color. Occasionally some birds are born with traits that make them more green. Occasionally some birds are born with traits that make them more blue.

STEP 3: Struggle to Survive Organisms compete for resources such as food, shelter, and mates. Those better suited to meeting these needs will survive. The birds face the challenge of blending in to survive.

STEP 3: Struggle to Survive Ugh!, so full… Not all members of the species will survive this competition. Only some will survive and have the opportunity to pass on their successful genes. EEP! Since blue-green birds stand out more in the habitat than green birds, more blue-green birds are eaten

STEP 4: Successful Reproduction Successful traits are passed to the next generation. Now, more members of the population are being born with the successful variation than those with the less suited trait. How has the allele frequency in the population changed? This is how a species changes over time (evolves) Now more green chicks than blue/ blue-green are being born.

STEP 5: Adaptation of the Species (Not included in the textbook) ? Adaptation – process by which a species becomes better suited to its environment. Hee, hee…

NATURAL SELECTION EXAMPLES Giraffe’s long neck Tuskless elephants (pg 122) OR Insecticide Resistance (pg 123) Pick your own species adaptation Additional Examples Peppered Moth Sickle Cell Anemia

NATURAL SELECTION EXAMPLE Sickle Cell Anemia

NATURAL SELECTION EXAMPLE Antibiotics vs. Bacteria Salmonella (bacteria that causes food poisoning) vs Salmonycin antibiotic (fights against Salmonella bacteria)

Discussion Questions According to Natural Selection, explain why human overpopulation exists? Are humans evolving?

SPECIATION (Steps to a new species) Speciation – The formation of a new species by the change of allele frequency (genetic variation) due to natural selection. Species: a group of organisms that can interbreed and produce fertile offspring. Steps of Speciation Separation: part of a population becomes isolated from the rest. What could cause separation? Adaptation: Natural selection improves the fit between species & environment created from changes in the gene pool. 3. Divergence: Differences in the gene pool accumulate between populations. Enough differences accumulate no longer allowing the populations to interbreed, which leads to a NEW SPECIES.

Example of Speciation 1 1 1 1. A population of fruit flies lay their eggs in some rotting bananas along a beach. 2. Separation - A hurricane washes the bananas and eggs out to sea and onto a nearby island. The flies hatch and are genetically isolated from the mainland fruit flies. Adaptation - Environmental conditions are different on the island, so the island flies evolve different adaptations. 3. Divergence - Natural selection changes physical features, food preferences, and mating rituals. 4. If the two populations were to by chance meet again they would unlikely mate with each other due to the differences in their gene pools creating differences in the characteristics listed above, especially mating rituals. 1. A population of fruit flies lay their eggs in some rotting bananas along a beach. 2. Separation - A hurricane washes the bananas and eggs out to sea and onto a nearby island. The flies hatch and are genetically isolated from the mainland fruit flies. Adaptation - Environmental conditions are different on the island, natural selection selects traits helping the species adapt to the island. 3. Divergence - Natural selection changes physical features, food preferences, and mating rituals. 4. If the two populations were to by chance meet again they would unlikely mate with each other due to the differences in their gene pools creating differences in the characteristics listed above, especially mating rituals. 2 3 4

Speciation

Madagascar – Examples of Speciation

Speciation Example – Flightless Island Birds

Speciation Experiment Fruit flies were taken from a single population and divided into two groups living in different cages (geographic isolation). One group lived on maltose (sugar)-food, and the other group lived on starch foods (differing environmental conditions). After many generations, it was found that some reproductive isolation had occurred due to the different food sources in the two isolated environments: "maltose flies" preferred other "maltose flies,“ "starch flies" preferred other "starch flies"

Speciation in Action? In the summer of 1995, at least 15 iguanas survived Hurricane Marilyn on a raft of uprooted trees. They rode the high seas for a month before colonizing the Caribbean island, Anguilla. These few individuals are the first of their species to reach the island. Evolutionary biologists would love to know what happens next: will the colonizing iguanas die out, will they survive and change only slightly, or will they become reproductively isolated from other iguanas and become a new species? We could be watching the first steps of speciation, but in such a short time we can't be sure.

Factors Contributing to Speciation Isolating Mechanisms Genetic Drift / Founders Effect

Isolating Mechanisms Genetic differences that prevent breeding between two species Pre-mating Examples - mating rituals, songs or calls, time of mating Post-mating Examples – hybrids are usually sterile

Genetic Drift Loss of genetic variation (alleles) brought about by chance, not adaptation. (occurs in small populations – Example: Founders Effect – on next slide) Examples cheetahs have little genetic variation (population decline 1,000s yrs ago endangered species lack genetic variation due to habitat loss Mountain Gorilla less than 720 left, due to habitat loss

Founders Effect Loss of genetic variation due to an isolated small founding population (could contain some rare variations (alleles) making the gene pool different from the original) Examples – Amish (founded by a few couples of German immigrants in 1770; unusually high frequency of dwarfism & polydactyly (extra fingers) Why? Because of continuous marring within the group, recessive gene diseases are more likely to show up in offspring

At what pace does evolution occur? GRADUALISM: states that evolution occurs slowly over time and includes many transitions PUNCTUATED EQUILIBRIUM: states that evolution occurs in short bursts followed by long periods of stasis (no evolving)