Copyright © 2009 Pearson Education, Inc. ◦ Adaptations: inherited traits that enhance an organism’s ability to survive and reproduce –Behavioral adaptations –Structural adaptations –Biochemical and physiological adaptations ◦ Evolution: descent with modification

DARWIN’S THEORY OF EVOLUTION Copyright © 2009 Pearson Education, Inc.

◦ Aristotle viewed species as perfect and unchanging ◦ Jean Baptiste de Lamarck (early 1800s) suggested that life on Earth evolves  Mechanism of change was use and disuse  Inheritance of acquired characteristics Copyright © 2009 Pearson Education, Inc.

A sea voyage helped Darwin frame his theory of evolution Copyright © 2009 Pearson Education, Inc. North America ATLANTIC OCEAN Great Britain Brazil The Galápagos Islands PACIFIC OCEAN Pinta Marchena Genovesa Santiago Fernandina Pinzón Isabela San Cristobal Española Florenza Daphne Islands Santa Cruz Santa Fe 40 miles Equator 40 km 0 0 Europe Africa South America Andes Argentina Cape Horn Cape of Good Hope PACIFIC OCEAN Equator New Zealand Australia Tasmania

◦ Sets sail around the world at age 22 ◦ 1840s- Writes first of essays describing evolution ◦ 1850s- Alfred Wallace writes theory identicle to Darwin ◦ publication of Darwin’s On the Origin of Species by Means of Natural Selection

◦ Theory:  Over time, present day species have arisen from ancestral species by natural processes (natural selection) or what is called descent by modification  Natural selection- the differential survival and reproduction of individuals within a population Copyright © 2009 Pearson Education, Inc.

 Artificial selection= the selective breeding of plants and animals that possess desired traits Copyright © 2009 Pearson Education, Inc. Terminal bud Lateral buds Leaves Kale Stem Brussels sprouts Cauliflower Cabbage Kohlrabi Wild mustard Flower clusters Flowers and stems Broccoli

 Note these important points #1 Individuals do not evolve: populations evolve #2 Natural selection can amplify or diminish only heritable traits; acquired characteristics cannot be passed on to offspring #3 Evolution is not goal directed and does not lead to perfection; favorable traits vary as environments change Copyright © 2009 Pearson Education, Inc.

 Ex: Development of antibiotic resistance in bacteria  Methicillin-resistant S. aureus (MRSA)  Vancomycin-resistant Enterococci (VRE)  Invasive Group A Streptococcus (GAS)  E. coli and Salmonella Copyright © 2009 Pearson Education, Inc.

What evidence do we have for evolution?

 Fossils: preserved remnants or impression of organism that lived in past  The fossil record shows that organisms have evolved in a historical sequence –The oldest known fossils are what organism? –The oldest eukaryotic fossils are a billion years younger –Multicellular fossils are even more recent Copyright © 2009 Pearson Education, Inc.

Example of geological strata- can be used to create a fossil record

Dickinsonia costata 2.5 cm

◦ Many fossils link early extinct species with species living today Copyright © 2009 Pearson Education, Inc. Pelvis and hind limb Rhodocetus (predominantly aquatic) Pakicetus (terrestrial) Dorudon (fully aquatic) Balaena (recent whale ancestor) Pelvis and hind limb

◦ Biogeography: the geographic distribution of species  Ex. Galapagos Copyright © 2009 Pearson Education, Inc.

◦ Comparative anatomy is the comparison of body structures in different species ◦ Homology is the similarity in characteristics that result from common ancestry Copyright © 2009 Pearson Education, Inc. Humerus Radius Ulna Carpals Metacarpals Phalanges HumanCatWhaleBat

 Some homologous structures are vestigial organs  Structure of marginal or no importance to organism Comparative anatomy and vestigial organs Copyright © 2009 Pearson Education, Inc. Pelvis and hind limb Rhodocetus (predominantly aquatic) Pakicetus (terrestrial) Dorudon (fully aquatic) Balaena (recent whale ancestor) Pelvis and hind limb

◦ Comparative embryology is the comparison of early stages of development among different organisms –When you were an embryo, you had a tail and pharyngeal pouches (just like an embryonic fish) Copyright © 2009 Pearson Education, Inc. Pharyngeal pouches Post-anal tail Chick embryo Human embryo

 Molecular biology: Comparisons of DNA between different organisms reveal evolutionary relationships –All living things share a common DNA code for the proteins found in living cells –We share genes with bacteria, yeast, and fruit flies –96% same DNA between us and chimps! Copyright © 2009 Pearson Education, Inc.

 Darwin was the first to represent the history of life as a tree Copyright © 2009 Pearson Education, Inc.

Tetrapod limbs Amnion Lungfishes Feathers Amphibians Mammals Lizards and snakes 2 Hawks and other birds Ostriches Crocodiles Amniotes Tetrapods Birds

THE EVOLUTION OF POPULATIONS Copyright © 2009 Pearson Education, Inc.

 Population: A group of individuals of the same species living in the same place at the same time  Evolution is the change in heritable traits in a population over generations Copyright © 2009 Pearson Education, Inc.

 Gene pool: 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 over time  What is necessary for evolution to happen??? Copyright © 2009 Pearson Education, Inc.

 Mutation: change in the nucleotide sequence of DNA  the ultimate source of new alleles Copyright © 2009 Pearson Education, Inc.

–Point mutation (single nucleotide change) or frameshift (can be multiple nucleotide change) –Results in missense, nonsense or silent mutation Copyright © 2009 Pearson Education, Inc.

–Every organism has spontaneous mutation rate –Mutagens increase this mutation rate Chemicals (caffeine, AZT, aflatoxin) UV radiation Ionizing radiation Copyright © 2009 Pearson Education, Inc.

 Chromosomal duplication : If a gene is duplicated, the new copy can undergo mutation without affecting the function of the original copy –Example: olfactory receptors in mammals Copyright © 2009 Pearson Education, Inc.

 Sexual reproduction shuffles alleles to produce new combinations How does sexual reproduction (including meiosis) lead to genetic variation? Copyright © 2009 Pearson Education, Inc.

 Sexual reproduction shuffles alleles to produce new combinations 1. Homologous chromosomes sort independently as they separate during anaphase I of meiosis 2. During prophase I of meiosis, pairs of homologous chromosomes cross over and exchange genes 3. Further variation arises when sperm randomly unite with eggs in fertilization Copyright © 2009 Pearson Education, Inc.

Parents Offspring, with new combinations of alleles Gametes Meiosis  and A1A1 Random fertilization A1A1 A2A2 A3A3 A1A1 A2A2 A3A3 A3A3 A1A1 A2A2 A1A1

Copyright © 2009 Pearson Education, Inc.

◦ Sexual reproduction alone does not lead to evolutionary change in a population –Alleles are shuffled, BUT the frequency of alleles and genotypes in the population does not change Copyright © 2009 Pearson Education, Inc.

◦ For a population to be in equilibrium for a specific trait, it must satisfy five conditions: 1.Very large population 2.No gene flow between 3.No mutations 4.Random mating 5.No natural selection A population in equilibrium Copyright © 2009 Pearson Education, Inc.

◦ The Hardy Weinberg principle:  Allele and genotype frequencies within a sexually reproducing, diploid population will remain in equilibrium unless outside forces act to change those frequencies  Often referred to as Hardy Weinberg equilibrium Copyright © 2009 Pearson Education, Inc.

◦ EXAMPLE:  Imagine that there are two alleles in a blue- footed booby population: W and w –W is a dominant allele for a nonwebbed booby foot –w is a recessive allele for a webbed booby foot Copyright © 2009 Pearson Education, Inc. Webbing No webbing

◦ Consider the gene pool of a population of 500 boobies –320 (64%) are homozygous dominant (WW) –160 (32%) are heterozygous (Ww) –20 (4%) are homozygous recessive (ww) Copyright © 2009 Pearson Education, Inc.

Phenotypes 320 ––– 500 Genotypes Number of animals (total = 500) Genotype frequencies Number of alleles in gene pool (total = 1,000) Allele frequencies WW Ww ww = ––– 500 = ––– 500 = w160 W w 640 W 800 1,000 = 0.8 W 200 1,000 = 0.2 w

◦ Frequency of dominant allele (W) = 80% = p –80% of alleles in the booby population are W ◦ Frequency of recessive allele (w) = 20% = q –20% of alleles in the booby population are w ◦ Frequency of all three genotypes must be 100% or 1.0 –p 2 + 2pq + q 2 = 100% = 1.0 Copyright © 2009 Pearson Education, Inc.

◦ What about the next generation of boobies? –Probability that a booby sperm or egg carries W = 0.8 or 80% –Probability that a sperm or egg carries w = 0.2 or 20% Copyright © 2009 Pearson Education, Inc.

Gametes reflect allele frequencies of parental gene pool W egg p = 0.8 Sperm w egg q = 0.2 W sperm p = 0.8 Eggs Allele frequencies Genotype frequencies Next generation: w sperm q = 0.2 WW p 2 = 0.64 ww q 2 = 0.04 wW qp = 0.16 Ww pq = WW0.32 Ww 0.04 ww 0.8 W0.2 w Allele frequencies don’t change

◦ For a population to remain in Hardy- Weinberg equilibrium for a specific trait, it must satisfy five conditions: 1.Very large population 2.No gene flow between populations 3.No mutations 4.Random mating 5.No natural selection Copyright © 2009 Pearson Education, Inc.

MECHANISMS OF MICROEVOLUTION Copyright © 2009 Pearson Education, Inc.

◦ IF five conditions for the Hardy-Weinberg equilibrium are not met  gene pool may change –Mutations are rare and random and have little effect on the gene pool –If mating is nonrandom, allele frequencies won’t change much (although genotype frequencies may) Copyright © 2009 Pearson Education, Inc.

◦ The three main causes of evolutionary change are 1. Natural selection 2. Genetic drift 3. Gene flow Copyright © 2009 Pearson Education, Inc.

◦ Natural selection  Process in which organisms with certain inherited traits are more likely to survive/reproduce than others –Consider the boobies: Would webbed or nonwebbed boobies be more successful at swimming and capturing fish? –What about sickle cell disease? Copyright © 2009 Pearson Education, Inc.

◦ Genetic drift –Genetic drift is a change in the gene pool of a population due to chance –In a small population, chance events may lead to the loss of genetic diversity (let’s flip a coin) Copyright © 2009 Pearson Education, Inc.

◦ Types of genetic drift –The bottleneck effect leads to a loss of genetic diversity when a population is greatly reduced Copyright © 2009 Pearson Education, Inc. Original population Bottlenecking event Surviving population

◦ Bottlenecks can be due to human intervention  Example: Hunting of northern elephant seal in 1890s reduced population to 30 individuals  Example: Breeders of pugs and Persians use so much inbreeding that gene pool has been dramatically reduced Copyright © 2009 Pearson Education, Inc.

o Bottlenecks can be due to catastrophic event  Example: Toba catostrophe theory 70,000 years ago where hominid population was reduced to 5,000-10,000 breeding pairs Copyright © 2009 Pearson Education, Inc.

 Types of genetic drift –Genetic drift produces the founder effect when a few individuals colonize a new habitat (ex. Martha’s Vineyard heritable deaf population) Copyright © 2009 Pearson Education, Inc.

◦ Gene flow –Gene flow is the movement of individuals or gametes/spores between populations and can alter allele frequencies in a population Copyright © 2009 Pearson Education, Inc.

◦ An individual’s fitness is the contribution it makes to the gene pool of the next and subsequent generations Copyright © 2009 Pearson Education, Inc.

1. Stabilizing selection favors intermediate phenotypes, acting against extreme phenotypes Copyright © 2009 Pearson Education, Inc.

2. Directional selection acts against individuals at one of the phenotypic extremes  Directional selection is common during periods of environmental change, or when a population migrates to a new and different habitat Copyright © 2009 Pearson Education, Inc.

3. Disruptive selection favors individuals at both extremes of the phenotypic range Copyright © 2009 Pearson Education, Inc.

Original population Frequency of individuals Original population Evolved population Phenotypes (fur color) Stabilizing selectionDirectional selectionDisruptive selection

So why don’t we run out of different alleles due to natural selection against “bad ones”?

◦ Sexual dimorphism: males and females show distinctly different appearance ◦ Intrasexual competition (or mate choice) involves competition for mates, usually by males Copyright © 2009 Pearson Education, Inc.

◦ Diploidy preserves variation by “hiding” recessive alleles (within the heterozygote) –A recessive allele is only subject to natural selection when it influences the phenotype in homozygous recessive individuals –Example: cystic fibrosis

◦ Balancing selection maintains stable frequencies of two or more phenotypes in a population  In heterozygote advantage, heterozygotes have greater reproductive success than homozygous –Example: sickle-cell anemia Copyright © 2009 Pearson Education, Inc.

◦ In frequency- dependent selection, two different phenotypes are maintained in a population –Example: African scale eating fish Copyright © 2009 Pearson Education, Inc. “Right-mouthed” “Left-mouthed” ’82’83’84’85’86’87’88’89’90 Sample year Frequency of “left-mouthed” individuals

◦ Some variations may be neutral variation, providing no apparent advantage/ disadvantage –Eample: human variation in fingerprints Copyright © 2009 Pearson Education, Inc.

1. Selection can only act on existing variation –Natural selection cannot conjure up new beneficial alleles 2. Evolution is limited by historical constraints 3. Adaptations are often compromises 4. Chance, natural selection and the environment interact Copyright © 2009 Pearson Education, Inc.