Genus (Evolution)

Featured in the 2001 comedy film Evolution (and its animated television series based on movie); these lifeforms are based on nitrogen, rather than carbon; and have a much faster metabolism than Earth creatures; as they are able to evolve into new species in a matter of hours or days, rather than millennia. They also have ten different fundamental bases in their DNA; whilst Earth organisms have only four. Exposure to great temperatures like explosions or fire causes these aliens to increase size tremendously.

Their origin is unknown. They arrive on Earth as blue-colored unicellular lifeforms inside a meteorite and soon some of them evolve to become multicellular, eventually spawning an entire ecosystem within the meteor's crater, which includes species analogous to lichens, worms and insects.

All Evolution lifeforms reproduce asexually, which is interesting given that this form of reproduction is often believed to be associated with slow, not fast, evolution. After a few days, some vertebrate analogues escape and start giving rise to several reptilianoid, and later mammalianoid forms, which threaten to take over Earth's entire ecosystem in no more than a few months. The only thing slowing down their progress is that they cannot breathe oxygen properly, making them slow and short-lived. Eventually however, some of the aliens do evolve the ability to breath oxygen and become far more dangerous. Based on the projections by Dr. Reed's team, it is estimated that the alien ecosystem will overwhelm the United States in two months.

In an attempt to wipe out the aliens, the USA military decides carpet-bomb the meteor site with napalm, supposedly destroying the center of alien activity. They were unaware of the creature's biological response to such explosions, however, and instead of killing the aliens the explosion results in the smaller lifeforms growing uncontrollably and fusing together to form a gigantic, amoeboid meta-organism. In the end, a weakness of the aliens is discovered: selenium, which is in the same position relative to nitrogen as arsenic is to carbon. Using grand quantities of selenium the giant alien is poisoned and killed.

In the animated television series, the aliens are referred to as "The Genus". The tv version does too have an intelligent form, called SCOPES.