Bacteria Conquer the World
THE C0MM0N ANCEST0R of all living things most likely was a bacterium, or prokaryote. Were it not for one line--which entered the long, complex, and mysterious pathway that led to eukaryotes--all of its progeny today would consist exclusively of bacteria. Even though they are no longer alone, bacteria still make up the larger part of the living world. Their evolution from the common ancestor illustrates the astonishing durability and versatility of prokaryotic forms of life. These qualities have allowed them to adapt to all sorts of different environments and to establish themselves and flourish in almost every kind of habitat. The diversity of bacteria is staggering and still incompletely inventoried. The reason for this success is simple: Bacteria are built to grow and multiply as fast as materially possible. They epitomize life at its rawest, with no frills.
A bioengineer attempting to construct a cell designed to proliferate as fast as possible could not come up with anything better than a bacterial cell. The bacterial genome is "streamlined" for fast replication. Genes are not split by introns and are crammed in the chromosome with hardly any space left for "junk" DNA. The chromosome itself is loosely structured, offering little impediment to the replication process. Furthermore, bacteria hardly ever stop duplicating their DNA and they manage to transcribe their genes and build all the RNAs and proteins they need for growth while they go about this activity. Some even start a second round of duplication before the first one is finished. As soon as two copies of their genome are available, they divide. As a result, it takes the average bacterium no more than twenty to thirty minutes to go through a complete growth and division cycle, as opposed to some twenty hours for the average animal or plant cell.