Evolution

Just a “Theory?”

Evolution

• Genetic change in species through time

• Microevolution: a change in a population’s allele frequencies

• Macroevolution: large scale patterns, trends among larger groups

Is God Involved?It depends on who you ask!

• Atheistic evolution: does not believe in God• Nontheistic evolution: divorce the two ideas;

believe in God, but believe that God has nothing to do with evolution; scientific approach is separate.

• Theistic evolution (gradual creation): creator was responsible for the initial creation event, but then “hands off.”

• Progressive evolution: creator is playing a role in directing evolution; guides it (implies a goal)

• Quick creation (Scientific Creationism”): believe in the biblical account of creation. (Genesis)

Craig Nelson, Indiana University

Darwin’s Theory

• Variation already exists within a species

• Scarcity of resources leads to competition

• Only the “fittest” survive to reproduce

• Natural selection: organisms with favorable variations survive and reproduce

Darwin’s Theory• Natural selection can lead to the formation of new

species

• Implies that many species once shared a common ancestor

• Adaptive radiation: where many species evolve from one

Change in gene frequency

• A population contains variation: same traits, but different alleles.

• A given allele may become more common, less frequent, or stay the same.

• So differences from point A to B on a time line can occur

Change over time

• Populations can evolve—individuals cannot evolve!

How do Gene Frequencies Change?

• Mutation

• Gene flow

• Genetic Drift

• Natural selection

• There is not a goal, as some cartoons depict

Evidence of Evolution

• Fossil

• Comparative anatomy

• Homologous structures analogous structures vestigial structures

• Comparative embryology

• Biogeography

• Comp biochemistry

Fossil evidence

• Deepest layers of rock are the oldest

• Can trace the changes that occurred in some species over time

• Not all species are fossilized

Comparative Anatomy

• Homologous structures: similar in skeletal structure

• May look different on the outside

• May vary in function

Comparative Anatomy

Suggest a common ancestor

Homologous Structures

Homologous Structures

Whale metacarpals are similar to our knuckle bones

Whale

Whale phalanges are similar to our finger bones

Vestigial Structures

• Structures or organs that appear to serve no purpose

• Examples: human tailbone, appendix

• Often homologous to structures that are useful in other species

• Suggest common ancestry

Comparative Embryology

• Embryos of certain species develop almost identically, especially in the early stages

• Similar genetic instructions

• Suggests that organisms descended from common ancestor

Biogeography

• Same environments in different parts of the world yield different organisms

• Ostrich, rhea, emu

Biogeography

Comparative Biochemistry

• Complex biochemical compounds such as cytochrome c, antibodies, and blood proteins are almost identical in many species

• Suggests high degree of relatedness and common ancestry

Microevolution

Changes occur in a population’s allele frequencies over time.

Microevolution

• Individuals in a population have same number and kinds of genes

• But forms of the gene may vary (alleles)

• Each individual is unique because of his combination of alleles

Microevolution

• One allele may be more or less common than others.

• One or more alleles may disappear

• One or more alleles may become more or less common

Causes of allele frequency changes

• Recombination• Mutation• Gene flow• Genetic drift• Natural selection

• All these shuffle the alleles

Recombination

• Creates new genetic varieties

• Sperm and ovum both bring 23 chromosomes

• Resulting in a zygote with a new combination of chromosomes distinct from either parent

Mutation

• Heritable change in the DNA

• Can be helpful, harmful, lethal, or neutral

• Can cause changes in the individual’s ability to survive and reproduce

Gene Flow

• Genes are transferred from one population to another.

• Migration• People travel to

another area and successfully mate with the population there.

Genetic Drift

• In small, reproductively isolated populations, chance can change the gene frequency.

• The smaller the population, the more dramatic the change

Genetic Drift• Very pronounced

after a bottleneck• A severe reduction

in population results in only a small population surviving

• Gene frequencies are altered

• Page 288-289

Natural Selection

• Usually the most important mechanism of evolution

• Environment selects the individuals with the best suited genotypes for survival and reproduction

Natural Selection

• For natural selection to cause evolution, it must select for or against one or more genotypes for a trait

• AA Aa aa• AA and aa• AA or aa… and so on

Frequency drops, but not to 0.

• The a will never completely disappear as long as there are heterozygotes (Aa)

• It is not a disadvantage to the heterozygote 

Selection against one of the homozygotes (aa)  Possible

  parent mating  patterns

Expected  offspring genotypes 

AA Aa aa

AA   X   AA 4

AA   X   Aa 2 2

 Aa   X   AA  2 2

 Aa   X   Aa  1 2 1

Total9

( 56% )

6( 38% )

1( 6%

Selection against aa

Directional Selection

• Allele frequencies tend to shift in a consistent direction

• In response to the environment, or a new mutation gets it started

• One end of the range becomes more common than the midrange

Peppered moth example; page 282

Stabilizing Selection

• Intermediate forms are favored.

• Tends to counter mutation, gene flow, and genetic drift

• Could favor the heterozygote

• Page 284

Disruptive Selection

• Forms at both ends of the range are favored; the intermediate forms are selected against

• Page 285

Speciation

An example of microevolution

What is a species?

• A species consists of organisms that can interbreed and produce fertile offspring

• A horse and a donkey can interbreed to produce a mule, but the mule is not fertile

New species emerge…

• As a result of reproductive isolation

• As a result of geographic isolation

• Populations become cut off from each other, and evolve separately

Reproductive isolation

• Any heritable feature of body form, function, or behavior prevents interbreeding

• Not necessary to have a physical separation

• Prezygotic or Postzygotic

• Pages 294-295

Geographical isolation• Physically separated• Could by mountains,

river, body of water separating islands, etc.

Geographical isolation

• Allopatric speciation: a physical barrier intervenes between populations and prevents gene flow among them

• Hawaii, Galapagos Islands, Florida Keys

Sympatric Speciation

• A species may form within the home range of an existing species

• No physical barrier

Parapatric Speciation

• Neighboring populations become distinct species, while maintaining a hybrid zone

Bullock’s oriole range

Baltimore oriole range

Adaptive Radiation• A burst of different species from a single lineage• May be due to physical access to a new habitat or• Key innovations may permit better survival

Classification

Five or six kingdoms?

The Old 5 Kingdom System

The Old 5 Kingdom System

• All the bacteria were grouped into Kingdom Monera

• Monera included eubacteria and archaebacteria

New relationships discovered

• In the 1970’s, with better methods to analyze biochemical makeup and sequence DNA, huge differences emerged between eubacteria and archaebacteria

Differences emerge• Archaebacteria live in

harsh environments• Subdivided into three

groups bases on habitat: methanogens, thermoacidophiles, and extreme halophiles

Archeabacteria

• Methanogens are anaerobic, and are found in swamps, marshes, sewage treatment plants, digestive tracts

• Produce methane

Archeabacteria

• Extreme halophiles live in very salty water

• Use salt to generate ATP

• Found in Dead Sea, Great Salt Lake

Archaebacteria

• Thermoacidophiles live in extremely hot and acidic water

• Temp of 110 C, and pH of 2

• Hot springs, volcanic vents, cracks on ocean floor that leak scalding water

The New 6 Kingdom System

Higher organisms are more closely related to the archaebacteria than to the eubacteria.

Showing relationships

• Phylogeny: evolutionary relationships between species, starting with ancestral forms and showing branches leading to descendants

Showing relationships

• Phylogeny can be shown in an evolutionary tree or a cladogram

Showing relationships

Showing relationships

Taxonomy

• Identifies, names and classifies species

• Binomial system• Scientific name is

Genus species • Homo sapiens