Have you noticed that animals are uniquely adapted

Have you noticed that animals are uniquely adapted to live in their habitats?

So Did Charles Darwin! 1831 -1836 - Darwin’s 5 -year voyage on the HMS Beagle

Darwin Observed… Species vary within a population Species overproduce Not enough resources for all offspring to survive Different island species closely resembled species on the nearest mainland. Population size is constant

Darwin's inferences… Individuals compete/struggle with each other for limited resources Only ‘successful’ individuals survive to reproduce Over many generations, a population will consist of the most successful kinds of individuals I think I shall call this “Origin of Species by means of Natural Selection”

• What is Evolutionary Theory?

Natural Selection & Candy # Silver Kisses # Purple Kisses # Striped Kisses Initial Population 25 Final Population 11 6 16 What ‘traits’ were selected for? Against? Would do you expect to happen to the frequency of each ‘phenotype’ in the next generation?

Natural selection Is… • Survival of those best adapted • Reproductive Fitness • Mindless and Mechanistic • A slow process Is NOT… • Purposeful • A guiding hand • Perfection

Evolution • Evolution: • the change over time of the genetic composition of populations • Natural selection: populations of organisms can change over the generations if individuals having certain heritable traits leave more offspring than others (differential reproductive success) November 24, 1859

Why do Populations Change? Adaptations: Inherited characteristics that better enable an organism to survive and reproduce Natural Selection = “Survival of those best adapted”… …FOR THE PRESENT CONDITIONS… BUT CONDITIONS CHANGE!

Evidence for Evolution 1. Direct observation 2. The Fossil Record 3. Comparative Anatomy (homology & convergent evolution) 4. Biogeography 5. Molecular Biology

Direct Observation Microbe evolution

Evolution evidence: The Fossil Record • Succession of forms over time • Transitional links • Vertebrate descent • Human Fossils

Evolution evidence: Comparative Anatomy • Homologous structures • Descent from a common ancestor • Vestigial organs Ex: whale/snake hindlimbs; wings on flightless birds

Convergent Evolution Distant ancestor; organisms adapted to same environment ANALAGOUS STRUCTURES

Evolution evidence: Comparative Embryology • Pharyngeal pouches, ‘tails’ as embryos

Evolution evidence: Molecular Biology • Similarities in DNA, proteins, genes, and gene products • Common genetic code

Evolution = ‘Descent with Modification’ = Change in population over time • • Change in gene pool Change in genotype Change in phenotype Change in adaptive advantage

Darwin's Finches 1) Finches on the Galápagos Islands resembled a mainland finch but there were more types. 2) Galápagos finch species varied by nesting site, beak size, and eating habits. 3) One unusual finch used a twig or thorn to pry out insects, a job normally done by (missing) woodpeckers (Darwin never witnessed this finch behavior).

Ground-dwelling finch – heavy beak, seed diet

Warbler-finch - thin beak - insect diet

Cactus finch - long, curved beak ; probing cactus flowers for nectar

• Darwin's Finches

RECAP: Natural Selection and Adaptation 1. Darwin decided that adaptations develop over time; he sought a mechanism by which adaptations might arise. 2. Natural selection was proposed by both Alfred Russel Wallace and Darwin as a driving mechanism of evolution caused by environmental selection of organisms most fit to reproduce, resulting in adaptation.

3. Because the environment is always changing, there is no perfectly-adapted organism. 4. There are three preconditions for natural selection. a. The members of a population have random but heritable variations. b. In a population, many more individuals are produced each generation than the environment can support. c. Some individuals have adaptive characteristics that enable them to survive and reproduce better.

5. There are two consequences of natural selection. a. An increasing proportion of individuals in succeeding generations will have the adaptive characteristics. b. The result of natural selection is a population adapted to its local environment.

6. Natural selection can only utilize variations that are randomly provided; therefore there is no directedness or anticipation of future needs. 7. Extinction occurs when previous adaptations are no longer suitable to a changed environment.

• Inherent variation is random (mutation, random mating, xing over, indep assortment) • Natural Selection NOT random • Differential reproductive success = FITNESS (not color, size, etc. ) Bacteria most fit!

SUMMARIZING • Natural selection is the driving force of evolution • Natural selection acts upon individuals (death or survival) but changes POPULATIONS • In fact: Theory of Evolution is more accurately called THEORY OF EVOLUTION BY NATURAL SELECTION

DRAWBACKS OF NATURAL SELECTION • Can only utilize variations that are randomly provided; there is no directedness or anticipation of future needs • Extinctions occur when previous adaptations are no longer suitable to a changed environment

History Lyell – Geologist who Darwin studied during his travels Lamarck – early evolutionist “use & disuse” Inheritance of acquired characteristics

Chapter 23 The Evolution of Populations

Population genetics • Population: a localized group of individuals belonging to the same species • Species: a group of populations whose individuals have the potential to interbreed and produce fertile offspring • Gene pool: the total aggregate of genes in a population at any one time • Population genetics: the study of genetic changes in populations • Modern synthesis/neo-Darwinism Individuals are selected, but populations evolve. ” “

Hardy-Weinberg Theorem • Serves as a model for the genetic structure of a nonevolving population (equilibrium) • 5 conditions: • 1 - Very large population size; • 2 - No migration; • 3 - No net mutations; • 4 - Random mating; • 5 - No natural selection

Hardy-Weinberg Equation p=frequency of one allele (A); q=frequency of the other allele (a); p+q=1. 0 P 2=frequency of AA genotype; 2 pq=frequency of Aa plus a. A genotype; q 2=frequency of aa genotype; p 2 + 2 pq + q 2 = 1. 0 # individuals = 2 alleles = genotype!!!!

Problem A plant population has red flowers (R) which are dominant to white (r). In 500 individuals, 25% are recessive phenotype. What is # of homozygous dominant and heterozygous for this trait?

How does evolution happen… 5 Reasons A change in the gene pool of a population over a succession of generations How # 1 - Genetic drift: changes in the gene pool of a small population due to chance (usually reduces genetic variability) TWO TYPES…

Genetic Drift Type I • The Bottleneck Effect: type of genetic drift resulting from a reduction in population (natural disaster) such that the surviving population is no longer genetically representative of the original population

Genetic Drift Type II • Founder Effect: a cause of genetic drift attributable to colonization by a limited number of individuals from a parent population

How #2: Gene Flow • 2 - Gene Flow: genetic exchange due to the migration of fertile individuals or gametes between populations (reduces differences between populations)

How #3: Mutation • 3 - Mutations: a change in an organism’s DNA (gametes; many generations); original source of genetic variation (raw material for natural selection)

How #4: Nonrandom mating • 4 - Nonrandom mating: inbreeding and assortive mating (both shift frequencies of different genotypes)

• How #5: NATURAL SELECTION NOT Random!!!! 5 - Natural Selection: differential success in reproduction; only form of microevolution that adapts a population to its environment

Population variation • Polymorphism: coexistence of 2 or more distinct forms of individuals (morphs) within the same population • Geographical variation: differences in genetic structure between populations (cline)

Variation preservation • Prevention of natural selection’s reduction of variation • Diploidy 2 nd set of chromosomes hides variation in the heterozygote • Balanced polymorphism 1 - heterozygote advantage (hybrid vigor; i. e. , malaria/sicklecell anemia); 2 - frequency dependent selection (survival & reproduction of any 1 morph declines if it becomes too common; i. e. , parasite/host)

Types of Natural selection • Fitness: contribution an individual makes to the gene pool of the next generation • 3 types: • A. Directional • B. Diversifying • C. Stabilizing

Sexual selection • Sexual dimorphism: secondary sex characteristic distinction • Sexual selection: selection towards secondary sex characteristics that leads to sexual dimorphism