Evolution

Ch 13

Historical Theories

• Anaximander (~2500 yrs ago)• Aristotle• Georges Buffon (1700’s)• Jean Baptist Lemark (late 1700’s - early1800’s)• Erasmus Darwin

Charles Darwin

18591874

Voyage of the HMS Beagle

On the Origin of Species…

• Descent With Modification

• By means of Natural Selection

How Did Darwin Come Up With His Ideas?

• Scientific Method• Key observations

– Traits vary in a population– Most traits are inherited from parent to offspring– More offspring are produced than the

environment can support (Thomas Malthus)

Trait Variation

Recap

• Limited resources• Overproduction of offspring• Heritable individual variation

– Therefore, survival depends partly on inherited features

Darwin’s Theory of Evolution

• In a varied population, individuals whose inherited characters best adapt them to the environment are more likely to survive and reproduce.

• Therefore, more fit individuals tend to leave more offspring than less fit individuals.

• Natural Selection is the mechanism– Reproduction (differential) is Key

Natural Selection

Artificial Selection

Observing natural selection

• Camouflage adaptations that evolved in different environments

A flower mantidin Malaysia

A leaf mantid in Costa Rica

Figure 13.5A

Pestacide Resistance

Pesticide application

Survivor

Chromosome with geneconferring resistanceto pesticide

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

Figure 13.5B

Antibiotic resistance

•The excessive use of antibiotics is leading to the evolution of antibiotic-resistant bacteria

Col

oriz

ed

SE

M 5

,600

Figure 13.13

Natural Selection Experiment• Darwin Finches

(Galapagos Finches)• Similar EXCEPT for

beaks– Beaks = specialization

Support for Descent with Modification

• Biogeography• Fossil Record• Molecular Biology, Biochemistry, Cell Biology• Comparative Anatomy

Biogeography

• Geographic distribution of species– Galápagos animals resembled species of the

South American mainland more than animals on similar but distant islands

– Organisms may have common ancestor

Fossil Evidence– Organisms evolved in a historical sequence

A Skull of Homoerectus

D Dinosaur tracks

C Ammonite casts

B Petrified tree

E Fossilized organicmatter of a leaf G “Ice Man”

Figure 13.3A–GF Insect in amber

Fossil EvidenceMany fossils link early extinct species with species

living today

Figure 13.3I

Comparative Anatomy• Comparison of body structures in different species

– Homology- similar characteristics resulting from common ancestry

– Homologous structures- features with different functions but structurally similar due to common ancestry

Human Cat Whale BatFigure 13.4A

Comparative Embryology•Comparison of early stages of development among different organisms

Post-analtail

Pharyngealpouches

Chick embryo Human embryoFigure 13.4B

Molecular Biology

•Comparisons of DNA and amino acid sequences between different organisms to reveal evolutionary relationships

Table 13.4

Unit of Evolution

•Evolution acts on individuals, affects whole populations

–Populations are the unit of evolution–Group of individuals of the same species living in the same place at the same time

Unit of Evolution

• Evolution is change in prevalence of heritable traits in population through time

• 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

Hardy-Weinberg Equilibrium• Frequency of alleles in a stable population

will not change over time– Very large population– Population is isolated– Mutations don’t alter gene pool– Random mating– All individuals are equal in reproductive success

• In reality, this never happens

Agents of Change

• Genetic Drift– Bottle neck affect– Founder affect

• Gene Flow• Mutation• Non Random Mating• Natural Selection

Variation•Extensive in most populations•Mutation and sexual recombination generate variation and can create new alleles.

Figure 13.11

Endangered species often have reduced variation

• Low genetic variability • May reduce the capacity of endangered species

to survive as humans continue to alter the environment

Figure 13.10

Types of Selection

Sexual Selection

• Sexual Dimorphism• Sexual Selection- where individuals with

certain characteristics are more likely to obtain mates than others. – Intrasexual selection– Intersexual selection

Diploidy

• Balancing selection– Heterozygote advantage– Frequency-dependent selection– Neutral Variation

Natural Selection is Limited

• Only act on existing variation• Historical constraints• Compromise• Chance, selection and the environment