EvolutionThe Process of Evolution (Variation,

Heredity and Differential Reproduction)

Important things to recall DNA

deoxyribonucleic acid, the macromolecule, composed of two polynucleotide chains in a double helix, that is the carrier of genetic information in all cells

Genes Heredity unit containing specific

genetic information. A gene can mutate to various forms called alleles.

Alleles Any of the alternative forms of a given

gene Allele Frequency

The relative proportion of all alleles of a gene that are of a designated type.

DNA (gene) → RNA → protein → trait

Definition of Evolution

Any process of change over time.

Classically A change in the relative frequencies of

heritable traits within a population across generations.

Modern A change in the distribution of relative

frequencies of genes (which code for heritable traits) within a population across generations.

Classical Evolution

A change in the relative frequencies of heritable traits within a population across generations

Relative frequency:

50% Tall plants 50% Short plants

55 generations later

25% Tall plants 75% Short plants

Modern Evolution

A change in the distribution of relative frequencies of genes (which code for heritable traits) within a population across generations

Differential Survival of Traits

Differential survival of traits in a population means that some characteristics will become more frequent while others occur less or are lost.

There are four known processes that affect the survival of a characteristic; or, more specifically, the frequency of an allele:

Mutation – error in duplication Genetic drift - stochasticity Gene Flow – movement of genes from pop. to pop. Natural selection

The production and redistribution of variation is produced by three of the four agents of evolution: mutation, genetic drift, and gene flow. Natural selection, in turn, acts on the variation produced by these agents.

Mutation occurs in the trait

Mutation directly changes gene frequencies

An example of a spontaneous mutation during the development of plant leaves

For evolution to occur via this mechanism, what has to be true of the mutation?

The mutation has to be heritable

The mutation of fruit flies with four wings is an inherited mutation

The population size is small Genetic drift – random fluctuations in the allele

frequencies

Generation 1p (frequency of R) = 0.7q (frequency of r) = 0.3

Generation 2p = 0.5q = 0.5

Only 5 of 10 plantsleaveoffspring

Only 2 of10 plantsleave offspring

Generation 3p = 1.0q = 0.0

Gene flow Immigration or emigration occurs based on the trait

Microevolution

Microevolution is the occurrence of small-scale changes in gene frequencies in a population over a few generations, also known as change at or below the species level.

Mechanisms of Evolution (cont.)

Natural Selection Natural selection, the last of the four forces, is

based on three principles: (a) there is VARIATION within a species and

this variation is HERITABLE (b) parents have more offspring than can

survive (c) surviving offspring have favorable traits

The mechanism by which it operates is termed survival of the fitter meaning differential mortality and fertility. Differential mortality is the SURVIVAL rate of

individuals before their REPRODUCTIVE AGE. If they survive, they are then selected further by differential fertility – that is, their total genetic contribution to the next generation.

VARIATIONVARIATION HERITABLE HERITABLE SURVIVAL TO REPRODUCE SURVIVAL TO REPRODUCE

Darwin’s Observations

Biogeography It is the study of distributions of

organisms, both past and present, and of related patterns of variation over the earth in the numbers and kinds of living things

Agriculture Selective breeding

Fossils Evidence of organisms no longer

present Evidence that many living

organisms were not present in the past

Geology New ideas about the age of the

Earth via plate tectonics

Economics Competition for resources and

the effects of overpopulation

Evolution by Natural Selection

(a mechanism of evolution)

Population level:

If variation exists and If variation is heritable and If differential reproduction (differential selection) exists

Then over time, those variations that enhance the ability of the organism to reproduce will increase in any population

Natural Selection leads to ADAPTATION

Adaptation

A biological adaptation is an anatomical structure, physiological process or behavioral trait that has evolved over a period of time by the process of natural selection that increases the likely hood of producing larger numbers of offspring or its reproductive success.

A heritable characteristic of an organism that helps it to survive and reproduce in a particular environment.

Adaptation vs. Acclimatization

Evolutionary biologists refer to an adaptation as a trait that evolved as the result of natural selection.

Physiologists use “adaptation” when they mean “acclimatization” – A nerve “adapts” to a continual stimulus or our eyes “adapt” to darkness

does not involve genetic change!

Adaptation refers to traits that are heritable

Acclimation: Changes in the structure or physiology of an individual over its lifetime

Examples: Increasing muscle mass via weightlifting

High altitude acclimation:

But, neither of these involves genetic change!

Human example of an adaptation: Sickle Cell Anemia

In North America, sickle cell anemia is uncommon and a disadvantage.

However, in other parts of the world, specifically areas where malaria is common, the occurrence of sickle cell anemia is greater.

Why?

Sickle Cell Anemia Because the heterozygous (SS, Ss, ss) Sickle Cell Anemia

genotype gives a higher resistance to malaria, however a homozygous genotype is still a disadvantage.

Sickle Cell Anemia Because the heterozygous (SS, Ss, ss) Sickle Cell Anemia

genotype gives a higher resistance to malaria, however a homozygous genotype is still a disadvantage.

DNA (gene) DNA (gene) →→ RNA → protein → trait RNA → protein → trait

Flattened tail – aids in swimming

Long, sharp claws – Aid in clinging to rocks

Salt gland – Allows drinking of salt water

Diving adaptations. While diving they: Reduce blood flow to

body surface- helps retain heat

Lower metabolic rate – conserves O2

Imperfect Adaptations

Multi-tasking may force an evolutionary compromise

Can’t simultaneously optimize distinct functions.

trait performance fitness

fitnesstrait

feeding

defense

thermoregulation

Adaptation – organisms are not perfectly adapted ( have to make due with your genetics)

Examples: panda thumb

All traits evolve from something else, so carry historical baggage thus can be “contrivances” (make do!)

HomologousHomologous structures which have a common origin.

Divergent Evolution

Divergent evolution is the process of two or more related species becoming more and more dissimilar.

The red fox lives in mixed farmlands and forests, where its red color helps it blend in with surrounding trees.

The kit fox lives on the plains and in the deserts, where its sandy color helps conceal it from prey and predators.

Convergent Evolution Convergent evolution is an evolutionary process in

which organisms not closely related independently acquire some characteristic or characteristics in common, or the evolution of species from different taxonomic groups toward a similar form.

This usually reflects similar responses to similar environmental conditions.

Structures that are the result of convergent evolution are called analogous structures or homoplasies; they should be contrasted with homologous structures which have a common origin.

WingsWings