EVOLUTION• Evolution = change over time.Evidence for evolution• 1.Fossil evidence—molds, casts, amber, ice, or become petrified. (Fossil record is incomplete---soft tissues not preserved)

• 2. Comparative anatomy— the study of the structures of different organisms.

-different kinds of organisms share similar structures—ex: bird, horse, human forelimbs.

-homologous parts—modified structures among different groups of descendants. (bird wing and insect wing are NOT) - the greater number of homologous parts two organisms share, the more closely related the organisms.

-vestigial structures—structures which have no function in one organism but are homologous to functional structures in another organism.

ex: whales have a nonfunctioning pelvis and leg bone.

ex: humans: appendix

3. Comparative embryology—compare the embryos of different organisms. (The more alike, the closer they are related)

4. Comparative biochemistry----compare the biochemical components of organisms. Ex: DNA, compare amino acid sequences of proteins (hemoglobin in humans and chimpanzees—very similar amino acid sequences.)

• Genetic evidence---

-genes and chromosomes can mutate and give rise to new alleles or genes, and therefore new proteins.

-meiosis and fertilization also reshuffle the genes= genetic recombination….leads to genetic variations.

-In any given population there is constant change.

--population=all organisms within a breeding group.

• Selective breeding—humans choose those organisms with the traits they desire and mate them. (Artificial selection)

• DNA---the DNA of humans and chimpanzees are 99% identical.

• Humans and other mammals---80% identical

• Direct observation—rapid evolution of bacteria—resistance to antibiotics. The few bacteria that are resistant to Penicillin will survive and reproduce—producing more bacteria that are also resistant to the Penicillin. Also a good reason to take your antibiotic prescription FULLY.

• The organisms that continue to live and reproduce are adapted to the new environment.

• Also occurs in weeds and insects—evolve to have a resistance to pesticides.

• Darwin’s explanation----(1809-1882) Theory of Natural Selection.

• HMS Beagle—ship’s naturalist• Became aware that organisms adapted to their environment

must change to remain adapted.• The Galapagos Islands---evolution=descent with modification• Giant tortoises, swimming iguanas—not found anywhere else• Plants and animals on the islands were similar to the ones on

the mainland.• Galapagos finches: adaptive radiation

The Theory of Natural Selection—

1. In nature there is a tendency of overproduction.

2. Not all offspring survive.

3. Variations (differences) exist in any population.

4. Variations are inherited.

5. Individuals with variations that make them more suited to their environment will live and produce more offspring that will have suitable traits like their parents.

6. The population as a whole changes as it becomes better adapted to its environment.

Adaptations—any structure,chemical or behavior

that allows an organism to survive better.

• Structural—structure—shell, finch beaks, fur, blubber

• Physiological---Chemical—octopus ink, snake venom, pheromones, chameleon skin color

• Behavioral---something the organism does—honeybee dance, insect acting like a leaf blowing in the wind.

• Gene pool—collection of all the genes present in a population.

Biological species

• Species- group of naturally interbreeding organisms that produce fertile offspring.

• (female horse x male donkey=mule=sterile)• (lion x tiger =tiglon {in captivity only} )

• Evolution of a new species=speciation.

Tiglon vs. Liger

Monarch vs. Viceroy

• Bad-tasting Monarch is mimicked by the good-tasting Viceroy butterfly.

Speciation-formation of new species over time. Can occur by:

• Geographic Isolation– separation of a population by a river, canyon, mountain, etc. The population becomes separated, evolves different adaptations, and become genetically different. Too different to interbreed.

• Reproductive Isolation---no interbreeding, and gene exchange is prevented. (sperm unable to fertilize egg)

• Genetic Drift--- a small number of individuals become isolated, a rapid change in numbers and kinds of genes. ( G.I. Followed by R.I.)

Speciation continued

• Polyploidy—individuals containing some multiple of the normal number of chromosomes. (Some plants are tetraploids—4n—often larger and produce larger flowers and fruits.) Ex. Wheat, cotton, daylilies.

• Adaptive Radiation ---Galapagos finches.

• Divergent evolution—when one species evolves into two or more species with different characteristics.

• Convergent evolution---species that are not closely related evolve similar traits. It usually occurs in unrelated species that have similar roles and live in similar environments.

Ex: butterfly and a bird

Ex: Mimicry ( Viceroy and the Monarch

Butterflies), Fish looks like coral, insect

looks like a leaf.

Ex: Coevolution—mutual adaptations evolve between a plant and its pollinator.

Tempo for Speciation

• Gradualism---slow, steady changes in a species.

• Punctuated equilibrium—slow evolution interrupted by short events of rapid evolution.

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Industrial Melanism and Microevolution

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Causes of Microevolution

• Genetic Mutations

– The raw material for evolutionary change

– Provides new combinations of alleles

– Some might be more adaptive than others

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Causes of Microevolution

• Gene Flow– Movement of alleles between populations

when:­ Gametes or seeds (in plants) are carried into another

population

­ Breeding individuals migrate into or out of population

– Continual gene flow reduces genetic divergence between populations

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Causes of MicroevolutionGenetic Drift

– Occurs by disproportionate random sampling from population

– Can cause the gene pools of two isolated populations to become dissimilar

– Some alleles are lost and others become fixed (unopposed)

– Likely to occur:­ After a bottleneck

­ When severe inbreeding occurs, or

­ When founders start a new population

– Stronger effect in small populations

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Genetic Drift

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Bottleneck Effect: A random event prevents a majority of individuals from entering the next generation. Next generation composed of alleles that just happened to make it. Can be followed by Genetic Drift.

Founder Effect: When a new population is started from just a few individuals. The alleles carried by population founders are dictated by chance and Formerly rare alleles will either:

­ Occur at a higher frequency in the new population, or Be absent in new population

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Founder Effect

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Natural Selection

• Results in:

– A change in allele frequencies the gene pool

– Improved fitness of the population

• Major cause of microevolution

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Directional Selection

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Stabilizing Selection

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Disruptive Selection

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Sickle-cell Disease

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Biological Species Definition

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Reproductive Isolating Mechanisms

• Reproductive isolating mechanisms inhibit gene flow between species

• Two general types:– (1) Prezygotic Mechanisms - Discourage attempts to

mate ­ Habitat Isolation

­ Temporal Isolation

­ Behavioral Isolation

­ Mechanical Isolation

­ Gamete Isolation

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Temporal Isolation

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Reproductive Isolating Mechanisms

• Two general types:

– (2) Postzygotic Mechanisms - Prevent hybrid offspring from developing or breeding

­ Zygote Mortality

­ Hybrid Sterility

­ Reduced F2 Fitness

ORIGIN OF LIFE

• Earth is about4.6 billion years old.

• Primitive atmosphere—Alexander Oparin 1936 proposed—

-methane, ammonia, hydrogen and water vapor.

Earth’s crust cooled, runoff from torrential rains created the oceans, UV radiation and lightning

-The energy sources broke the bonds in the gas molecules releasing atoms to form simple organic compounds.

1953—Miller and Urey’s experiments---presence of amino acids

First organisms—ocean= primordial soup– anaerobic, prokaryotic, heterotrophic.

--then the evolution of autotrophs—chemosynthetic, then photosynthetic---then oxygen in the atmosphere, then aerobic respiration, eukaryotes, ozone production=ozone layer (blocks harmful UV radiation), then life on Earth’s surface.

-Endosymbiosis: A theorized process in which early eukaryotic cells were formed from simpler prokaryotes.