Chapters 20-22, Evolution

Evolution:

Science: The word means to know.
Webster's Definition:
1) Systematized knowledge derived from observation and experiments carried on to determine the principles underlying what is being studied.
2) Biology: The science of life, of all living matter and the life processes common to all living things.

Vocab:
-Genotype: Genes of an organism for a particular trait or traits. Ex: BB or Ab
-Phenotype: Visible expression of a genotype. Ex: brown eyes or attached earlobes.
-Allele: An alternative form of a gene (occurs at the same locus on homologous chromosomes).

Evolution During the 19th Century:

1) Lamarck (before Darwin) 1744-1829
-First biologist who really believed in evolution.
-Believed that

a) Descent with modification occurs
b) Organisms adapted to their environment
c) Supported the theory of inheritance of acquired characteristics - Giraffes in Figure 20.1, page 396

-However, experimentation in genetics show us that phenotypic changes acquired during an individual's life are not passed on to its offspring.

2) Charles Darwin
-Hypothesized that common descent occurs and that natural selection results in adaptation to the environment.
-Concluded that adaptation to the environment caused diversification , and this diversification causes the origin of new species.
-Today we say that evolution is descent with modification.

a) The descent of organisms from common ancestors with the development of genetic and phenotypic changes over time that make them more suited to the environment.
*Change is the operative word.
b) If organisms do not change and adapt to the changing environment, they become extinct.
c) Extinction is a big part of evolution, it is normal.

3) The Hardy-Weinberg Principle
-Modern method used to day to tell us what causes evolution.
-Method was developed by G. H. Hardy, an English mathematician, and W. Weinberg, a German physician, early last century.
-Five conditions must be met so that original proportion of the genotype in a population remain constant (a situation that is virtually impossible):

a) No mutation.
b) No gene flow: migration of alleles into or out of the population does not occur.
c) Random mating (by chance); not according to phenotype.
d) Large population with insignificant change in allele frequency - no genetic drift
e) No selection- no selective favors over one genotype than another.

If these conditions are not met, there is evolution.

- Selection

a) Natural selection is the environmental selection of organisms most fit to reproduce, resulting in adaptation.
b) Variations are essential, they make adaptation to the environment possible. Ex: pesticides.

-Mutations during sexual reproduction cause new variations to arise.

4) Evidence for Evolution

-Paleontology- The study of fossils
-Biogeographic Separation
-Comparative Anatomy
-Biochemistry and Molecular Data

A. Fossil:
-any past evidence of an organism that has been preserved in the Earth’s crust.
a) There are intermediate fossils that show intermediate changes, they show a stepping stone in major changes
b) Archaeopteryx: The intermediate between dinosaurs and birds.

B. Biogeography:
- Study of plant and animal distribution on Earth.
-States that related forms evolved in one location then diversified as they continued to spread into other, more accessible areas.
a) Example: Australian continent separated from the other continents about 50 million years ago
b) Marsupials came earlier, placental mammals later.
c) Marsupials have evolved in a different, isolated area as a result of natural selection in relation to similar environments. See Figure 21.18, page 428.

C. Homologous Structures:
a) Structures that are similar because they were inherited from a common ancestor. Not necessarily common function.
-Example: Birds from reptiles: scales changed to feathers.
-Vertebrate forelimbs: same bones, different functions, birds and bats for flight, penguin for swimming, horses for running.
b) Then we have vestigial structures: these are found on current species but are not functional.
-Example: Snakes, loss of legs, but some still have a pelvic girdle, hips with little legs (whales too).
-Humans have a tailbone but no tail.
-Human embryos possess gill slits like a fish and later exhibit a tail.
-We also possess a fine fur (lanugo) during fifth month of development.
c) Analogous structure: different evolutionary origin, similar function.
-Example: Bat wing and butterfly wing.

D. Biochemistry and Molecular Data: (video watched in class)