Evolution

Genetic Variation and Evolution Evolution: changes through time Species accumulate difference Descendants differ from their ancestors New species arise from existing ones Individuals don’t evolve – populations do

A brief history of evolution Charles Darwin was born on February 12, 1809 in Shrewsbury, England. From 1831 to 1836 Darwin served as naturalist aboard the H.M.S. Beagle on a British science expedition around the world. He observed much variation in related or similar species of plants and animals that were geographically isolated from each other. These observations were the basis for his ideas.

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A brief history of evolution Darwin presumed that populations of individuals changed over time, and, in 1844, he developed the concept of the driving force for evolution. It wasn’t until many years later that he published his idea. “I have called this principle, by which each slight variation, if useful, is preserved, by the term Natural Selection.” —Charles Darwin from "The Origin of Species“, 1859

EVIDENCE OF EVOLUTION STRUCTURAL ADAPTATIONS MIMICRY CAMOUFLAGE MILLIONS OF YEARS http://evolution.berkeley.edu/evolibrary/home.php http://science.howstuffworks.com/animal-camouflage2.htm Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.

EVIDENCE OF EVOLUTION STRUCTURAL ADAPTATIONS MIMICRY CAMOUFLAGE MILLIONS OF YEARS PHYSIOLOGICAL ADAPTATIONS CHANGE IN A METABOLIC PROCESS WHAT DO YOU HEAR ABOUT IN THE NEWS ABOUT SOME BACTERIA? Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.

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OTHER EVIDENCE OF EVOLUTION FOSSILS ANATOMY HOMOLOGOUS STRUCTURES - similar structures that evolved from a common ancestor. http://evolution.berkeley.edu/evolibrary/home.php Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.

OTHER EVIDENCE OF EVOLUTION FOSSILS ANATOMY HOMOLOGOUS STRUCTURES ANALOGOUS STRUCTURES - various structures in different species having the same appearance, structure or function but have evolved separately, thus do not share common ancestor http://evolution.berkeley.edu/evolibrary/home.php Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.

OTHER EVIDENCE OF EVOLUTION FOSSILS ANATOMY HOMOLOGOUS STRUCTURES ANALOGOUS STRUCTURES VESTIGIAL STRUCTURE - structures or attributes that have apparently lost most or all of their ancestral function in a given species, but have been retained EMBRYOS http://evolution.berkeley.edu/evolibrary/home.php Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.

MECHANISMS FOR EVOLUTION HOW CAN THE GENE POOL CHANGE? MUTATION - permanent alteration of the nucleotide sequence of the genome GENETIC DRIFT - the change in the frequency of an allele in a population due to random sampling of organisms GENE FLOW - the transfer of alleles or genes from one population to another NONRAMDOM MATING - mating that has not occurred due to chance SELECTION - survival and reproduction or elimination of individuals with certain genotypes (genetic compositions), by means of natural or artificial controlling factors. WOULD THESE THINGS EFFECT A LARGE POPULATION OR A SMALL POPULATION MORE?

GENETIC DRIFT GENE FLOW - MIGRATION MUTATION ALL IMAGES: http://evolution.berkeley.edu/evolibrary/home.php Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.

Five agents of evolutionary change The Hardy-Weinberg Principle - genetic equilibrium

Genetic equilibrium is a basic principle of population genetics. Hardy–Weinberg principle states that the genotype frequencies in a population remain constant or are in equilibrium from generation to generation unless specific disturbing influences are introduced. Those disturbing influences include: non-random mating new mutations selection random genetic drift gene flow

Evolution of species Based on 3 mechanisms 1. Sources of variation 2. Method of selection for those characteristics that would be passed on 3. A mechanism for retaining changes

1. Sources of variation Genetic diversity thru mutations that are not lethal Physical or behavioral traits Sexual reproduction between genetically different individuals

1. Sources of variation

2. Method of selection Reproductive fitness is the method of selection. Competition, escaping from and eluding predators Finding a good mate

Selection Natural selection: environmental conditions determine which individuals in a population produce the most offspring 3 conditions for natural selection to occur Variation must exist among individuals in a population Variation among individuals must result in differences in the number of offspring surviving Variation must be genetically inherited

Natural selection: mechanism of evolutionary change Natural selection: proposed by Darwin as the mechanism of evolution individuals have specific inherited characteristics they produce more surviving offspring the population includes more individuals with these specific characteristics the population evolves and is better adapted to its present environment

Natural Selection Darwin: Evolution is descent with modification Darwin knew nothing of genes, but what he did have were two observations and a little inference that provided the motive force for evolution. Darwin: Evolution is descent with modification

Natural Selection Observation 1: Organisms generally have more offspring than can survive to adulthood. Observation 2: Offspring are not identical. There is variation in their appearance, size, and other characteristics.

Natural Selection Survival of the “fittest.” Inference: Those organisms that are better adapted to their environment have a greater likelihood of surviving to adulthood and passing these characteristics on to their offspring. Survival of the “fittest.”

Survival of the “fittest.” Darwin’s theory for how long necks evolved in giraffes

Selection Artificial selection: a breeder selects for desired characteristics

3. Maintenance of Variation Frequency-dependent selection: depends on how frequently or infrequently a phenotype occurs in a population Negative frequency-dependent selection: rare phenotypes are favored by selection Positive frequency-dependent selection: common phenotypes are favored; variation is eliminated from the population Strength of selection changes through time

Negative Frequency-Dependent Selection Side-blotched Lizards Infectious Diseases Male common side-blotched lizards come in three throat-color patterns: orange, blue, and yellow. Each of these forms has a different reproductive strategy: orange males are the strongest and can fight other males for access to their females; blue males are medium-sized and form strong pair bonds with their mates; and yellow males are the smallest and look a bit like female, allowing them to sneak copulations. Like a game of rock-paper-scissors, orange beats blue, blue beats yellow, and yellow beats orange in the competition for females. As a result, populations of side-blotched lizards cycle in the distribution of these phenotypes. In one generation, orange might be predominant and then yellow males will begin to rise in frequency. Once yellow males make up a majority of the population, blue males will be selected for. Finally, when blue males become common, orange males will once again be favored. As a particular human population is infected by a common strain of microbe, the majority of individuals in the population become immune to it. This then selects for rarer strains of the microbe which can still infect the population because of genome mutations; these strains have greater evolutionary fitness because they are less common.

Positive Frequency-Dependent Selection The scarlet kingsnake, a harmless species, mimics the coloration of the eastern coral snake, a venomous species typically found in the same geographical region. Predators learn to avoid both species of snake due to the similar coloration, and as a result the scarlet kingsnake becomes more common, and its coloration phenotype becomes more variable due to relaxed selection. This phenotype is therefore more "fit" as the population of species that possess it (both dangerous and harmless) becomes more numerous. Mimicry

WHAT IS SPECIATION? GEOGRAPHIC ISOLATION REPRODUCTIVE ISOLATION http://evolution.berkeley.edu/evolibrary/home.php Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.

Fitness and Its Measurement Fitness: A phenotype with greater fitness usually increases in frequency Most fit is given a value of 1 Fitness is a combination of: Survival: how long does an organism live Mating success: how often it mates Number of offspring per mating that survive