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