BIO 7: Lecture 27 Preview
Scientific Theories, Laws,
Principles = ideas receiving support from many studies and are therefore widely
Support from Mendel's discovery of genes. Early weakness in Darwin's idea: no explanation for source of random heritable variation.
1860's Mendel discovers genes = sources of heritable variation
Mutations create new forms of heritable information
Meiosis and sexual reproduction create new combinations of heritable information
Lots of genetic variation (many different combinations of alleles) observed in natural populations.
Evolution = change in the average phenotype in a population; change in genotype and allele frequencies
Support from ecology: Many studies show that environments have carrying capacities.
Microevolution due to natural selection observed directly in organisms with short generation times
(What is the adaptation? What is the selective agent in the environment?)
e.g. drug-resistant bacteria and DDT-resistant mosquitoes arise
e.g. Industrial Melanism (example in lab) of peppered moths in Britain
Support from plant and animal breeding studies: Artificial Selection: reproduction of certain types chosen by humans
Support from population geneticists: Populations' gene pools can change due to other factors besides natural selection.
Factors changing populations
Migration (Gene flow)
Macroevolution inferred from studies of other isolated populations
e.g. Fruitflies in the Hawaiian Islands: 8 volcanic islands formed 1-2 million years ago
2000-2500 miles away from mainlands
have several hundred species of fruitflies
fruitflies related to each other and mainland species, but adapted to different parts of different islands
e.g. Cichlid fish in Lake Victoria: several hundred species in lake filled 12,000 years ago
Formation of new species requires reproductive isolation.
Can occur when a population is separated into 2 subpopulations by a geographical barrier.
Can occur in the same location due to other barriers
A recent example of speciation: Hawthorn flies used hawthorn fruit for food before colonists came to America. Colonists brought apple trees. Apples ripen a few weeks later than hawthorns. Some hawthorn flies used apples for food. Now 2 species: hawthorn fruitflies and apple maggot fruitflies. What is the reproductive isolation barrier?
Evolution by Natural Selection (or descent with modification) is like a low-budget remodeling job: Each species is not an ideal "house" built from the ground up with a specific design. Rather, species start with a structure passed on from an ancestor and make use of modifications that become available through mutations.
Support from embryological studies
Support from anatomy studies: homologous structures and vestigial structures