Chapter 15 Evolution - All Sections 15.1 - 15.3

Unit 8-Evolution

15.1 Darwin’s Theory of Natural Selection

15.2 Evidence of Evolution

15.3 Shaping Evolutionary Theory

Name _________________________ Period _______

15.1 Darwin’s Theory of Natural Selection• Main idea:

• Objectives– Discuss the evidence that convinced Darwin that

species could change over time.– List the four principles of natural selection.– Show how natural selection could change a

population• New Vocabulary

– Selective breeding, Artificial selection, Natural selection, Evolution

Developing the Theory of Natural Selection

• Charles Darwin boarded the HMS Beagle in 1831.

• Most believed the world was about 6,000 years old.

• During the ship’s five year voyage, Darwin made extensive collections of rocks, fossils, plants and animals.

• He also read Charles Lyell’s Principles of Geology – a book proposing the Earth was millions of years old.


• In 1835, the Beagle arrived in the Galapagos Islands off the coast of South America.

• Darwin began to collect mockingbirds, finches, and other animals on the four islands.

• He noticed that the different islands seemed to have their own, slightly different varieties of animals.

HMS Beagle


• Almost every specimen that Darwin had collected on the islands was new to European scientists.

• Darwin suspected populations from the mainland changed after reaching the Galápagos.

Galápagos Islands


• Darwin hypothesized that new species could appear gradually through small changes in ancestral species.

• Darwin inferred that if humans could change species by artificial selection (selective breeding), then perhaps the same process could work in nature.


• Darwin called his theory Natural Selection

Natural SelectionNatural Selection

• He reasoned that, given enough time, natural selection could modify a population enough to produce a new species.

Basic Principles of Natural Selection

The Origin of Species

• Darwin published On the Origin of Species by Means of Natural Selection in 1859.

• Today, biologists use the term evolution to define changes in groups of organisms through time.

• Darwin’s theory of natural selection is NOT the same as evolution. Natural selection is a means of explaining HOW evolution works.

15.2 Evidence of Evolution• Main idea:

• Objectives: – Describe how fossils provide evidence of evolution.– Discuss morphological evidence of evolution.– Explain how physiology and biochemistry provide

evidence of evolution.

• New Vocabulary Derived trait Ancestral trait Homologous structure Vestigial structure Analogous structure

Embryo Fitness Mimicry Camouflage

Support for Evolution• The theory of evolution states that all organisms

on Earth have descended from a common ancestor.

• The fossil record offers some of the most significant evidence of evolutionary change.– Fossils provide a record of species that lived

long ago.– Fossils show that ancient species share

similarities with species that now live on Earth.

• The giant armadillo-like glyptodont, Glyptodon,is an extinct animal that Darwin thought must be related to the living armadillos of today.

• The fossil record provides information for determining the ancestry of organisms and the patterns of evolution.

Support for EvolutionThe Fossil Record

Support for Evolution

Two major classes of traits:•Derived traits are newly evolved features, such as feathers, that do not appear in the fossils of common ancestors.•Ancestral traits are more primitive features, such as teeth and tails, that do appear in ancestral forms.

The Fossil Record


• Transitional fossils provide detailed patterns of evolutionary change for ancestors of many modern animals, including mollusks, horses, whales and humans.

Example:•Archeopteryx

Shares features of both dinosaurs and birds.

The Fossil Record


• Homologous structures are anatomically similar structures inherited from a common ancestor.

• The forelimbs of vertebrates are adapted for different uses, but they all have similar bones.

• Similar structure; different function.

Comparative Anatomy


• Vestigial structures are the reduced forms of functional structures in other organisms.

• Evolutionary theory predicts that features of ancestors that no longer have a function for that species will become smaller over time until they are lost.• Examples: Snake pelvis and

human appendix.

Comparative Anatomy


• Analogous structures can be used for the same purpose and can be similar in construction, but are not inherited from a common ancestor.

• Show that functionally similar features can evolve independently in similar environments.

• Different structure; same function;

Comparative Anatomy


• An embryo is an early pre-birth stage of an organism’s development.

• Vertebrate embryos exhibit homologous structures during certain phases of development but become totally different structures in the adult forms.

Comparative Embryology

Comparative Biochemistry• Common

ancestry can be seen in the complex metabolic molecules that many different organisms share.


Geographic Distribution

• The distribution of plants and animals that Darwin saw during his travels first suggested evolution to Darwin.

Rabbit in Europe Mara in S. America


• Scientists have confirmed and expanded Darwin’s study of the distribution of plants and animals around the world in a field of study now called biogeography.

• Evolution is intimately linked with climate and geological forces.

Geographic DistributionSupport for Evolution

Adaptation

• An adaptation is a trait shaped by natural selection that increases an organism’s reproductive success.

• Fitness is a measure of the relative contribution an individual trait makes to the next generation. It is often measured as the number of reproductively viable offspring that an organism produces in the next generation.

• Camouflage allows organisms to become almost invisible to predators. Some species have evolved morphological adaptations that allow them to blend in with their environments.

• Mimicry is another morphological adaptation that allows one species to evolve to resemble another species.

AdaptationTypes of Adaptation

• Antimicrobial resistance - An antibiotic is a medicine that slows or kills the growth of bacteria.– Some bacteria have

evolved a resistance to certain antibiotics.

People infected with resistant bacteria can never get rid of it.

AdaptationTypes of Adaptation


• Main idea:

• Objectives:– Discuss patterns observed in evolution.– Describe factors that influence speciation.– Compare gradualism with punctuated equilibrium.

• Review Vocabulary– Allele: alternative forms of a character trait that can be

inherited.


• Hardy-Weinberg Principle• Genetic drift• Founder effect• Bottleneck• Punctuated Equilibrium• Sexual selection

New Vocabulary

Mechanisms of Evolution

• Darwin’s theory of natural selection remains the central theme of evolution

• Scientists of today know that natural selection is not the only mechanism of evolution

• Evolution occurs at the population level, with genes as the raw material.


• Hardy-Weinberg Principle states that when allelic frequencies remain constant, a population is in genetic equilibrium.

Population Genetics

Even though the number of owls doubled, the ratio of gray to red owls remained the same.


• p2 + 2pq + q2 = 1• This equation allows us to determine the

equilibrium frequency of each genotype in the population:

• homozygous dominant (p2)• heterozygous (2pq)• homozygous recessive (q2)

– Note the sum of these frequencies equals one.

Population Genetics


A population in genetic equilibrium must meet all five conditions

•The population is very large•No immigration or emigration•Mating is random•Mutations do not occur (no new variations)•Natural selection does not occur

Population Genetics

• Genetic Drift is a change in the allelic frequencies in a population that is due to chance.

• In smaller populations, the effects of genetic drift becomes more pronounced, and the chance of losing an allele becomes greater.

• Examples: Founder Effect & Bottleneck

Mechanisms of EvolutionGenetic Drift

• Founder Effect occurs when a small sample of a population settles in a location separated from the rest of the population

Genetic Drift

• Alleles that were uncommon in the original population might be common in the new population.


• Alleles that were uncommon in the original population might be common in the new population.

• Bottleneck occurs when a population declines to a very low number and then rebounds

Mechanisms of EvolutionGenetic Drift

Can decrease genetic variety.

• A population in genetic equilibrium experiences no gene flow, however, few populations are isolated

• Random movement of individuals between populations reduces differences between populations

Mechanisms of EvolutionGene Flow

• Rarely is mating completely random in a population.

• Usually individuals mate with individuals in close proximity.

Nonrandom mating


• This promotes inbreeding and could lead to a change in allelic proportions favoring individuals that are homozygous for particular traits.

• A mutation is a random change in genetic material.

• Occasionally mutations provide an advantage to organisms and become more common in subsequent generations.

• Basis upon which natural selection works.

Mechanisms of EvolutionMutation

Select the individuals that are best adapted for survival and reproduction•Stabilizing selection – eliminate extreme

expressions• Birth Weights

•Directional selection – makes organisms more fit.• Peppered Moths

•Disruptive selection – process that splits a

population into two groups. • Lake Erie Water Snakes

Mechanisms of EvolutionNatural Selection

• Sexual selection operates in populations where males and females differ significantly in appearance.– Males are largest and most colorful

in the group– More likely target for predators yet

bodies enhance reproductive success• Examples: Peacocks & Deer

Natural Selection


• prevents reproduction by making fertilization unlikely.– Eastern and Western

meadowlarks similar in appearance but their mating songs separate them behaviorally.

Reproductive IsolationPrezygotic Isolation

• Occurs when fertilization has occurred but a hybrid offspring cannot develop or reproduce.

Reproductive IsolationPostzygotic Isolation

A Liger is the offspring of a male lion and a female tiger. Ligers are sterile.

• A physical barrier divides one population into two or more populations.

Speciation

Allopatric speciation

• For speciation to occur, a population must diverge and then be reproductively isolated.

• Species evolves into a new species without a physical barrier

Speciation

Sympatric speciation

Apple maggot flies lay eggs on apples or hawthorns depending on the type of fruit the grew up on.

• For speciation to occur, a population must diverge and then be reproductively isolated.

• Can occur in a relatively short time when one species gives rise to many different species in response to the creation of new habitat or some other ecological opportunity.

Patterns of EvolutionAdaptive Radiation (aka divergent evolution)

• Follows large-scale extinction events

Cichlid fish of Lake Victoria in Africa.

• The relationship between two species might be so close that the evolution of one species affects the evolution of the other species.

• Mutualism – occurs when two species benefit each other.

Coevolution

Patterns of Evolution

• The plant evolves a chemical defense

• The insects evolve the biochemistry to resist the defense

• Response continues to escalate.

Patterns of EvolutionCoevolution• Coevolutionary arms race – one species can

evolve a parasitic dependency on another species.

• A plant and an insect that is dependent on the plant for food

• Unrelated species evolve similar traits even though they live in different parts of the world.

• Occurs in environments that are geographically far apart but have similar ecology and climate.

Patterns of EvolutionConvergent Evolution

• Punctuated equilibrium explains rapid spurts of genetic change causing species to diverge quickly.

Rate of Speciation

Patterns of Evolution

• Evolution proceeds in small, gradual steps = gradualism.

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Chapter 15 Evolution - All Sections 15.1 - 15.3

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