Modern Theory of Evolution

I. Much of Darwin’s theory of evolution is still widely accepted among the scientific community.– A. Weakness of Darwin’s theory:

» 1. He has not offered an explanation for causes and transmission of variations

II. Hugo DeVries (early 1900’s)- Mutation Theory– A. Studied the Primrose

» 1. DeVries discovered that these plants sometimes reproduced offspring that were structurally different then they bred “true” in the following generations

a. He called these “changes” Mutationsb. As a result, DeVries believed evolution of

new species occurred due to large amounts of sudden variations

III. Population Genetics– A. A population is a group of organisms of the same

species living together and capable of interbreeding» 1. According to modern evolution:

a. individuals do not evolveb. populations evolve as new generations arrive

» 2. All of the genes present in a given population is known as the gene pool

a. Over time, gene pools change as a result of natural selection (mutations and sexual repro.)

b. Natural Selection places a “survival value” on specific genes, gene pools change as a function of the environment, and new species form

– Gradualism or Punctuated Equilibrium?

EvolutionEvolution– Based on observations, scientists have Based on observations, scientists have

suggested that various things have suggested that various things have changed over long periods of timechanged over long periods of time

– Geologic EvolutionGeologic Evolution- Changes that have - Changes that have occurred, and are still occurring, to the occurred, and are still occurring, to the EarthEarth over time over time

– Organic EvolutionOrganic Evolution- Changes that have - Changes that have occurred, and are still occurring, to occurred, and are still occurring, to living thingsliving things over time over time

Geological Time- The Earth is believed to Geological Time- The Earth is believed to be 4.5 billion years oldbe 4.5 billion years old–4.5 billion = 4,500,000,000 = 4.5 X 104.5 billion = 4,500,000,000 = 4.5 X 1099

–As a result of these large numbers, As a result of these large numbers, scientists have named large chunks of scientists have named large chunks of time based on dominant events of the time based on dominant events of the time.time.

– c. The fossil record seems to support this

-a. Darwin, however, explained evolution as a gradual accumulation of variations

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SuddenChanges

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**Known as: Punctuated Equilibrium

**Known as: Gradualism

Mechanism of Evolution

Natural Selection-Natural Selection-

"Survival of the fittest“"Survival of the fittest“

The survival and reproduction of individuals w/ certain advantageous characteristics

. Charles Darwin (1830)

– 1. Overproduction

– 2. Struggle for existence (survival)

– 3. Variation

– 4. Survival of the fittest

– 5. Natural selection

– 6. Evolution of new species

Natural selection is based on . . .Natural selection is based on . . . Non-random survivalNon-random survival

– Albino squirrelsAlbino squirrels Non-random matingNon-random mating

– Mate selectionMate selection» Woman’s choiceWoman’s choice

Non-random fecundityNon-random fecundity– Production of offspringProduction of offspring

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Modes of Modes of SelectionSelection

Stabilizing Selection favors the intermediate phenotype out of a range of phenotypes. The extremes in variation are selected against. Infants weighing significantly less or more than 7.5 pounds have higher rates of infant mortality. Selection works against both extremes.

After a few years of extensive use, DDT lost its effectiveness on insects. Resistance to DDT is a genetic trait that the presence of DDT in the environment made into a favored trait. Only those insects resistant to DDT survived, leading over time to populations largely resistant to DDT.

Directional Selection

Disruptive Selection favors individuals at both extremes of variation: selection is against the middle of the curve. This causes a discontinuity of the variations, causing two or more morphs or distinct phenotypes.

Evidence for EvolutionEvidence for Evolution

A.A. The fossil recordThe fossil record1.1.Geological time scale - major eventsGeological time scale - major events

Evidence from Comparative Anatomy Comparative Anatomy- the study of structural

similarities and differences between living things» 1. Homologous Structures- parts of different

organisms that have similar structure, but different forms and functions

a. human arm and hand, whale flipper, cat leg, bat wing, bird wing

» 2. analogous structures- parts of different organisms that have similar forms and functions, but different internal structure (example: wing of a bird, wing of an insect)

» 3. Vestigial Structuresa. remnants of structures that were once

functional in an ancestral form– -appendix, wisdom teeth, coccyx (tailbone)

Homologous Structures- same Homologous Structures- same structure: different functionstructure: different function

A.A. The fossil recordThe fossil record

Living fossils, like the coelacanth, ginkgo, and horseshoe crab, are examples of organisms that are relatively unchanged from their distant ancestors. Exterior of a horseshoe crab, an example of a living fossil.

B. Comparative Embryology– 1. Structurally different species show

common patterns in embryological development

»a. presence of gill slits, 2-chambered hearts, tails

»b. the longer the embryos show similarities, the more closely related the species

C. Evidence from DNA– 1. Each individual organism has its own

specific DNA structure (DNA fingerprint)

– 2. The closer the structure of DNA between organisms (species), the closer the evolutionary relationship

TWO TYPES OF DATINGTWO TYPES OF DATING• Relative Time

• I went to the store

• Example-

•I then got gas in the car

• I then drove home

• Puts event’s into a sequence but doesn’t identify their actual date of occurrence...

• Absolute Time• Example

• At 3 PM I went t the store

• I got gas for my car at 3:45 PM

• I drove home at 4 PM

• Shows actual dates

Absolute Dating– A. Radioactive Dating

»1. by using the half-life of certain radioactive elements, it is possible to calculate the age of certain fossils by their rate of decomposition

Relative Dating– A. Different layers of bedrock can be

examined

»1. generally, the deeper the layer, the older the rocks and the fossils preserved within them

»2. index fossils have been identified to set a standard for comparative dating