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.

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

NorthAmerica

Great Britain Europe

Africa

Equator

Australia

Tasmania

NewZealand

Cape ofGood Hope

SouthAmerica

An

des

Cape Horn

Tierra del Fuego

GalápagosIslands

PacificOcean

AtlanticOcean

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

Human Cat Whale Bat

– Molecular biology

Human Rhesus monkey Mouse Chicken Frog Lamprey

Last commonancestor lived26 million yearsago (MYA),based onfossil 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 shepherd Yorkshire terrierEnglish springer

spanielMini-dachshund Golden retriever

Hundreds tothousands of years

of breeding(artificial selection)

Ancestral dog

• These five canine species evolved from a common ancestor through natural selection

Figure 13.4C

African wilddog

Coyote Fox Wolf Jackal

Thousands tomillions of years

of natural selection

Ancestral canine

• The evolution of insecticide resistance is an example of natural selection in action

Chromosome with geneconferring resistanceto insecticide

Additionalapplications of thesame insecticide willbe less effective, andthe frequency ofresistant insects inthe populationwill grow

Survivor

Insecticideapplication

• 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

Webbing No 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 = 0.64 160/500 = 0.32 20/500 = 0.04

640 W 160 W + 160 w 40 w

800/1,000 = 0.8 W 200/1,000 = 0.2 w

Number of allelesin gene pool(total = 1,000)

Allele frequencies

Recombinationof alleles fromparent generation

Next generation:

Genotype frequencies

Allele frequencies

SPERM EGGS

0.64 WW 0.32 Ww 0.04 ww

0.8 W 0.2 w

WWp2 = 0.64

WWqp = 0.16

Wwpq = 0.16

wwq2 = 0.04

W sperm

p = 0.8

w sperm

q = 0.2

W e

gg

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

13.11 There are several potential causes of microevolution

Originalpopulation

Bottleneckingevent

Survivingpopulation

– 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

Fre

qu

en

cy

of

ind

ivid

ua

ls

Originalpopulation

Phenotypes (fur color)

Originalpopulation

Evolvedpopulation

Stabilizing selection Directional selection Diversifying 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…