Ciliates, such as paramecium, are another interesting group with a completely different approach to life. They are usually described as "single celled", and by

Ciliates, such as paramecium, are another interesting group with a completely different approach to life. They are usually described as "single celled", and by implication simple, but the cell in this case is much more complex than one of ours. Animals (and for that matter, plants) develop from a single-celled zygote, into a multicellular organism, which eventually dies, after producing gametes to merge into zygotes to continue the cycle. Ciliates have an analogous, but totally different, approach. A newly "born" ciliate has a "micronucleus", similar to one of ours, from which it makes multiple copies of its DNA to form a "macronucleus", which does all the work. Perhaps gene expression in the macronucleus even changes in a way that learns about its environment. But eventually, the ciliate mates, or goes through a sort of self-conjugation event, dividing into more than one cell, each of which gets a new micronucleus formed by recombination. These cells discard the macronucleus, forming a new one from the new micronucleus. It's sort of like a multicellular organism dying, since whatever the old macronucleus learned will be forgotten. (Perhaps that's the point, if the environment has changed, requiring a new approach.)