Slides 1-13

Evidence for Evolution 1. Fossils show change over time scientists can date fossils & use them to support the theory of evolution common ancestors reveal whether species are related –Anatomy of living species also shows relatedness

How Anatomy supports Evolution 2.Homologous Structures Traits similar in different species because they share a common ancestor Ex: human arm, dog front limb, horse leg, whale fin “ Look the Same”

3. Analogous structures Distantly related species have structures that have the same function but are different in structure Ex: wing of butterfly & bird “ Work the Same” How Anatomy supports Evolution

4. Vestigial structures Structures reduced in size & often unused Remains of functional structures inherited from an ancestor Ex: leg & hip bones in pythons & whales

How do new species form? 1.Geographic Isolation When members of a population are separated Ex: polar, grizzly, & black bears

2. Reproductive Isolation When members of a population can’t breed even though they live nearby Ex: different mating seasons or different mating calls

Different Types of Evolution 1.Divergent evolution 2.Convergent evolution 3.Coevolution 4.Adaptive radiation

1. Divergent Evolution Isolated populations evolve independently Ex: polar & grizzly bears changed independently due to different habitats

2. Convergent Evolution Unrelated species become more alike because they live in similar environments Ex: shark & dolphin

3.Coevolution Species that interact closely adapt to one another Ex: flowers & hummingbirds

4. Adaptive Radiation Evolution of many diverse species from one common ancestor Ex: Galapagos finches discovered by Darwin

Population Genetics: Evolution at the Gene Level

Population all of the individuals of a species that live together in one place at one time.

Natural Selection: populations changing in response to their environment as individuals better adapted to the environment leave more offspring

4 Steps of Natural Selection: 1.Overproduction 2.Genetic Variation 3.Struggle to survive (limited resources) 4.Successful reproduction

Allele Frequency The relative amount of an allele of a gene within a population (%) Example If 100 individuals make up a population and 50 are homozygous dominant, 25 are heterozygous, and 25 are recessive, what is the allele frequency of the dominant allele?

Allele Frequency You Try! If 300 individuals make up a population, 150 are homozygous dominant, 100 are heterozygous, and the rest are recessive, what is the allele frequency of the recessive trait?

How does Natural Selection Affect Allele Frequency Mutations provide the raw material on which natural selection acts Evolution depends on variations because it is the only way that differences among organisms are created Acts on Populations not individuals by changing the % of alleles in the population

Survival of the Fittest If individuals having certain genes are better able to produce mature offspring than those without them, the frequency (#) of those genes will increase  Survival  Survival: Making it to reproductive age  Fitness  Fitness: Producing enough offspring

Different Lines of Evidence Wolf LineageWolf Lineage: all dogs are descendent from the Grey wolf Darwin’s FinchesDarwin’s Finches: all 13 species are descendent of a South American species Whale DNA

Genetic Drift Mutations that take place because of random fluctuations of gene frequencies due to small population size Example: Ellis-van Creveld syndrome A rare form of dwarfism that includes extra fingers and toes– Amish population of eastern Pennsylvania, which has intermarried over many generations.

Gene Flow Changes in the gene pool of a population because of the introduction of genes from another population by migration. Example: the gene pool in southeast Asia was changed when U.S. Soldiers had children with Vietnamese women during the Vietnam war.

Founder Effect Changes in a population when a small population moves to a new location bringing only a small fraction of the genes and variation of the parent population. Example: Galapagos Finches

Over-hunting, predation or natural disaster leads to a population that no longer represents the original. Organisms are recessive at almost all alleles MutationsMutations: deformed Claws, low sperm count, coat variation Example: Cheetahs (2 bottleneck events) 1 st :10,000 years ago 2 nd : 1980’s Bottleneck Effect

Types of Natural Selection Stabilizing Directional Diversifying

Stabilizing Selection Extremes from both ends of the frequency distribution are eliminated. The most common form of natural selection. A real-life example is that of birth weight of human babies. Too small or too big you die in childbirth

Directional Selection Individuals at either end of the distribution are favored. The distribution shifts towards the left or right, depending on which one is favored. What we usually think of as natural selection

Diversifying (Disruptive) Selection Both extremes are favored at the expense of middle phenotype species formationA mechanism for species formation without geographic isolation

CLADISTICS A Cladogram is a branching diagram that depicts species divergence from common ancestors. They show the distribution and origins of shared characteristics. Cladograms are testable hypotheses of phylogenetic relationships.

Questions?