Definition of Evolution A process by which modern organisms have descended from ancient organisms and/or Any change in the frequency of an allele in a given gene pool

The voyage of the Beagle North America Great Britain Europe Africa Equator Australia Tasmania New Zealand Cape of Good Hope South America Andes Cape Horn Tierra del Fuego Galápagos Islands Pacific Ocean Atlantic Ocean

Darwin’s Contemporaries Lamark Weismann Lyell Wallace Malthus

Fossils and the fossil record strongly support the theory of evolution –Hominid skull The study of fossils provides strong evidence for evolution –Petrified trees

–Ammonite casts –Fossilized organic matter in a leaf

–Scorpion in amber –“Ice Man”

The fossil record shows that organisms have appeared in a historical sequence Many fossils link early extinct species with species living today –These fossilized hind leg bones link living whales with their land-dwelling ancestors

Other evidence for evolution comes from –Biogeography –Comparative anatomy –Comparative embryology Evidence to validate the evolutionary view of life HumanCatWhaleBat

–Molecular biology HumanRhesus monkeyMouseChickenFrogLamprey Last common ancestor lived 26 million years ago (MYA), based on fossil evidence 80 MYA 275 MYA 330 MYA 450 MYA

Darwin observed that –organisms produce more offspring than the environment can support –organisms vary in many characteristics –these variations can be inherited Darwin saw natural selection as the basic mechanism of evolution –Human involvement-Breeding Darwin proposed natural selection as the mechanism of evolution

–Example of artificial selection in animals: dog breeding German shepherdYorkshire terrier English springer spaniel Mini-dachshundGolden retriever Hundreds to thousands of years of breeding (artificial selection) Ancestral dog

These five canine species evolved from a common ancestor through natural selection Figure 13.4C African wild dog CoyoteFoxWolfJackal Thousands to millions of years of natural selection Ancestral canine

The evolution of insecticide resistance is an example of natural selection in action Chromosome with gene conferring resistance to insecticide Additional applications of the same insecticide will be less effective, and the frequency of resistant insects in the population will grow Survivor Insecticide application

A gene pool is the total collection of genes in a population at any one time Microevolution is a change in the relative frequencies of alleles in a gene pool Microevolution is change in a population’s gene pool over time

Hardy-Weinberg equilibrium states that the shuffling of genes during sexual reproduction does not alter the proportions of different alleles in a gene pool –To test this: The imaginary, nonevolving population of blue-footed boobies The gene pool of a nonevolving population remains constant over the generations WebbingNo webbing

We can follow alleles in a population to observe if Hardy-Weinberg equilibrium exists Phenotypes Genotypes Number of animals (total = 500) WW 320 Ww 160 ww 20 Genotype frequencies 320 / 500 = / 500 = / 500 = W160 W w40 w 800 / 1,000 = 0.8 W 200 / 1,000 = 0.2 w Number of alleles in gene pool (total = 1,000) Allele frequencies

Recombination of alleles from parent generation Next generation: Genotype frequencies Allele frequencies SPERMEGGS 0.64 WW0.32 Ww0.04 ww 0.8 W0.2 w WW p 2 = 0.64 WW qp = 0.16 Ww pq = 0.16 ww q 2 = 0.04 W sperm p = 0.8 w sperm q = 0.2 W egg p = 0.8 w egg q = 0.2

Public health scientists use the Hardy-Weinberg equation to estimate frequencies of disease- causing alleles in the human population –Example: phenylketonuria (PKU) Connection: The Hardy-Weinberg equation is useful in public health science

The population is very large The population is isolated Mutations do not alter the gene pool Mating is random All individuals are equal in reproductive success Five conditions are required for Hardy-Weinberg equilibrium

Genetic drift is a change in a gene pool due to chance –i.e., the change in allele frequencies over time –Genetic drift can cause the bottleneck effect and vice versa There are several potential causes of microevolution Original population Bottlenecking event Surviving population

–or the founder effect

Gene flow can change a gene pool due to the movement of genes into or out of a population Mutation changes alleles Natural selection leads to differential reproductive success

Genetic Drift and/or Founder Effect Can Lead to Another example of Evolution: Adaptive Radiation Adaptive radiation describes the rapid speciation of a single or a few species to fill many ecological niches. This is an evolutionary process driven by mutation and natural selection. Three Types: –General adaptation. A species that develops a radical new ability can reach new parts of its environment. An example of general adaptation is bird flight. –Environmental change. A species that can, in contrast to the other species in the ecosystem, successfully survive in a radically changed environment will probably branch into new species that cover the new ecological niches created by the environmental change. An example of adaptive radiation as the result of an environmental change is the rapid spread and development of mammalian species after the extinction of the dinosaurs. –Geographic isolation. Isolated ecosystems, such as archipelagos and mountain areas, can be colonized by a species which upon establishing itself undergoes rapid divergent evolution. Darwin's finches are examples of adaptive radiation occurring in an archipelago.

Natural selection results in the accumulation of traits that adapt a population to its environment –If the environment should change, natural selection would favor traits adapted to the new conditions Adaptive change results when natural selection upsets genetic equilibrium

Many populations exhibit polymorphism and geographic variation

Some variations may be neutral, providing no apparent advantage or disadvantage…or does it? –Example: human fingerprints Not all genetic variation may be subject to natural selection

Low genetic variability may reduce the capacity of endangered species to survive as humans continue to alter the environment –Studies have shown that cheetah populations exhibit extreme genetic uniformity –Thus they may have a reduced capacity to adapt to environmental challenges Connection: Endangered species often have reduced variation

An individual’s Darwinian fitness is the contribution it makes to the gene pool of the next generation relative to the contribution made by other individuals Production of fertile offspring is the only score that counts in natural selection The perpetuation of genes defines evolutionary fitness

13.19 There are three general outcomes of natural selection Frequency of individuals Original population Phenotypes (fur color) Original population Evolved population Stabilizing selectionDirectional selectionDiversifying selection

Sexual selection leads to the evolution of secondary sexual characteristics –These may give individuals an advantage in mating Sexual selection may produce sexual dimorphism

Why? –historical constraints –adaptive compromises –chance events –availability of variations Perfection is impossible…