ARCHIVE - Evolution

Doing Science

Epistemic values and an introduction to Evolutionary theory

Epistemic values

From Michael Ruse Mystery of Mysteries (1999): a contrast to cultural values

Promote the "truth-seeking" nature of science

Epistemic values: a good theory should show

Predictive accuracy - the power to make forecasts about what one will find.
Internal coherance - the parts must fit together
External consistency - must fit with other known facts.
Unifying power - unites previously unrelated material under "a single explanatory roof"
Fertility - makes predictions beyond the original observations
Simplicity - Ockham's razor: the simpler of two competing hypotheses is more likely to be true. Is this too close to nonepistemic values? An aesthetic preference?

Evolution

What are we trying to explain?

Why are there so many species (plants, animals, etc.)?

How are species related to each other?

By what process are species formed?

Theory must accommodate these observations

the earth is very old

there are fossils of extinct forms

diversity and complexity increase with time

organisms show "homologous" structure and biochemical similarities (DNA)

Natural selection as the mechanism

similar theories were developed independently by Charles Darwin and Alfred Russell Wallace

Definitions

population — a group of interbreeding individuals of the same species, in a more-or-less definable area.

fitness — the total number of offspring that an individual leaves behind when it dies

adaptation — a genetically-determined trait that helps an organism to survive and reproduce in a particular environment; the process by which such traits evolve.

Evolution by natural selection is a consequence of these conditions

potential for rapid reproduction — most organisms can produce more offspring than the environment is capable of supporting

because of condition 1, the availability of resources (food, water, space, light, etc.) will limit the size of the population

where there is heritable variation in traits that influence reproductive success, individuals with those traits should become increasingly predominant in the population.

As a consequence of the three conditions listed above, over a long period of time, the frequency of alleles that result in higher fitness should increase over time.

Note that neither Darwin nor Wallace knew anything about the mechanisms of inheritance.

The precise definition of evolution, according to the modern "Neodarwinian synthesis" is: Change in the relative frequencies of alleles in a population over time. (This definition will make more sense after the third evolution talk.)

If over a long time, populations become so different that they are no longer capable of interbreeding, they are then considered to be different species. This outcome of the evolutionary process is called speciation.