"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
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).
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
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!).