Population Genetics

"Geneticists know that strength of a species comes from its diversity from the fact that the population as a whole can respond in mnay different ways to many different situations"
- Eric S. Lander, MIT

The more genes two animals have in common, the closer they are "related" (not by blood, but by evolution) to one another. Therefore, different levels of classification exist to illustrate this relationship. There are seven levels of classification, the highest group being a kingdom, and the lowest group a species (the others between the two extremes are, in order, phylum, class, order, family, and genus). Many thousands of different organisms may belong to a kingdom, but only one to a species. For example: humans, dogs, porcupines, rats, eagles, and salmon all belong to the same kingdom (Kingdom Anamalia), but only humans belong to the species sapiens and only dogs to Canis domesticus. Two organism are more closely "related" as they approach the level of species. This also means they have more genes in common. Taxonomists (scientists who classify living organisms into the seven groups) define a species as any group of closely related organisms that can produce fertile offspring. Sometimes, members of the same species will look alike (all brown bears look alike and all humpbacked whales look alike) and other times they won't (such as German Shepherds and Chihuahuas, which are both members of the same species).

The level of species can be further divided into smaller segments. A population is the smallest unit of a species and is made up of organisms of the same species. All the hemlock trees in a forest make up a population of hemlock trees, and all the rattlesnakes on an island make up a population of rattlesnakes, and so forth. Sometimes, a population will physically alter over time to suit the needs of its environment. This is called a cline, and can make members of the same species look different.

A subspecies is a distinct population of a species. A good example of a subspecies is the western flicker which has red wings and looks different than the eastern flicker which has yellow wings. The two types of birds belong to the same species, though, because they can produce fertile offspring (sometimes with orange wings!).