Caenorhabditis elegans is a species of nematode, or roundworm, which grows to about 1 millimetre (less than 1/16th of an inch) long. It is one of the simplest known animals to possess a nervous system, which makes it a useful model species for standing a range of components of advanced life, including the genome.
Better known simply as C. elegans, this roundworm lives on bacteria and vegetation. The species is somewhat unusual: it has male individuals and hermaphroditic individuals, but no true females. The males are an extremely small minority; the vast majority are hermaphrodites, meaning they possess both male and female reproductive organs. After being born, they mature through four stages, and in the absence of food the larvae can enter a hardier but non-aging stage. They are found in a range of environments in nature, but not normally in pure soil, since it lacks the organic deposits they feed on. Advanced research into C. elegans began in the 1970s, when biologists realized that this species offered a number of avenues for interesting biological research. As the simplest animal with a nervous system, it offers the easiest model for mapping out an entire network of neurons.
Geneticists have subsequently discovered that C. elegans has importance for their work, as well. Its genome was fully sequenced in 1998, making it the first animal sequenced. Although it is a small and comparatively simple organism, according to research published in Trends in Parasitology, its genes contain the data necessary to form many of the organs and functions present in larger and more complex organisms like human beings, like sexual differentiation, feeding and digestive processes, and so on. Overall, according to Rutgers University, C. elegans shares slightly over one-third of its genetic base code with human beings. This still makes up only a small proportion of the human genome, since C. elegans has only a few percent as much genetic material as human beings.
This does hold out a number of interesting options for genetic research, however. Much like fruit flies, C. elegans are easy to breed in the laboratory and use for experiments. They can even be easily frozen and revived, particularly as larvae. Genetic researchers have devised methods known as RNA interference which can be used to selectively eliminate genes from the C. elegans genetic code, or introduce genes back in. This has confirmed a number of important hypotheses about DNA. First, scientists were able to eliminate more than four out of every five genes from the C. elegans DNA without interfering with the basic survival of the worms, meaning that even its simplified genetic code is mostly junk left over from millions of years of evolution. Moreover, although roundworms and mammals are theoretically only distantly related, in the one-third of its code shared with human beings, genes derived from human cells can be introduced into the C. elegans genetic code and serve the same function as their original roundworm equivalents. Such experiments have corroborated important theories about genetic evolution and the interconnectedness of the origins of all animal species.