5 Factors responsible for evolutionary change
1) nonrandom mating
2) mutations
3) genetic drift
4) genetic flow
5) natural selection
sexual dimorphism
individuals of most sexually reproducing species have a distinctively male of female phenotype (males are flashier and more aggressive)
-has to do with nonrandom mating
Natural Selection: Stabilizing Selection
selects against phenotype extremes, individuals with average phenotypes are favored.
-babies with average weights are more likely to survive (the mother isn’t burdened and the baby isn’t too small to get food)
Natural Selection: Directional Selection
may favor phenotypes at one of the extremes of the normal distribution; over time one phenotype replaces another in frequency
-speckled rats survive better in the patchy canopy shade, then the trees get cut down so the white rat survives better
Natural Selection: Disruptive Selection
the average is selected against, more than one phenotype is favored but it isn’t the average
-white beach with black rocks, the average speckled rats won’t survive
Hardy-Weinburg requirements
- no mutations
- no gene flow
- yes random mating
- no genetic drift
- no selection
evolution can be detected by…
…noting any deviation from the equilibrium, there would be a change in allele frequencies
-this is microevolution
Evidences of Evolution:
- fossils
- biogeography
- comparative anatomy
- molecular biology
- embryology
Date a fossil using half-life
- us radioactive isotopes found in the fossils, these have a particular half life (the time it takes for 1/2 of the isotope to change into another stable element)
- if a fossil has organic matter, than 1/2 of the Carbon-14 isotope will be changes to Nitrogen-14 in 5730 years (the next half-life would be 11,460
Relatively date a fossil
- fossils found in the stratum of sedimentary rock are a local sample of the organisms that existed at the time
- strata at one location often can be correlated with strata at another location by similar fossils known as index fossils
- like peeling off wallpaper of an old house, oldest is buried deepest
Biogeography
the study of geographic distribution of a species
- Australian wildlife evolved on the island continent in isolation from regions where early placental mammals diversified
- we find species where they are because they evolved from ancestors that inhabited those regions
Comparative Anatomy
comparison of body structures between different species
- the same skeletal remains make up the forelimbs of humans, cats, whales, and bats (all mammals)
- this means we all descended from a common ancestor
homologous, analogous, and vestigial structures
- similar structures that have adapted to different functions
- traits inherited from the common ancestor, such as spines and tails
- similarity due to convergent evolution, not a common ancestor
- had to meet the same needs, so they developed the same things on their own
- squid eyeballs and cat eyeballs
- had to meet the same needs, so they developed the same things on their own
- body structures that no longer function
- wings on flightless birds (like ostriches), human tailbones
Molecular Biology
- if two species have lots of genes and proteins with sequences of monomers that match closely, the sequences must have been copied from a common ancestor
- all living organisms have the same genetic code, the greater the % in nucleotide sequences the more related they are
Embryology
comparing the embryos of organisms to show common ancestry
