Why do some cells not have a nucleus?

The first living things appeared on earth around 3.7 billion years ago. They were small, unicellular organisms that didn't look much different from some of today's bacteria. Modern cells at this stage of development are called prokaryotes (previously mostly prokaryotes; literally: pronuclear) because they have no nucleus, no separate compartment for the genetic material.

This simple way of life is still very successful today. The prokaryotes (from Latin pro meaning before and from Greek karyon for core, stone, nut) have produced a rich variety of species due to their particularly high speed of reproduction and evolution and have been able to adapt to all possible environmental conditions - and still do .

The fact that the biosphere does not only accommodate such microbe-like beings goes back to an event through which eukaryotes (or eukaryotes), namely cells with a real cell nucleus and hereditary material packaged in it, emerged - completely different, much more complex organisms. A completely new epoch began in evolution: all plants and animals as well as fungi are eukaryotes. Today's multicellular organisms in all their manifestations would not exist without this development step and therefore also no people who are happy about them and can trace their still largely mysterious peculiarities.

It is very likely that the eukaryotes emerged from bacteria-like precursors. How this could happen is not easy to see, because any intermediate stages of the two types of cells no longer exist, not even fossil; and the end product is too different from the original shape. Thanks to the possibilities of modern biology, light comes into the long impenetrable darkness of the past. Many a kinship between characteristics of the two cell types that is to be demonstrated always leaves the path of development

This article is included in Spectrum of Science 6/1996