It seems that all eukaryotic cells either have, or once had (and then lost) mitochondria. In other words, possession of mitochondria is a sine qua non of the eukaryotic condition
The point I want to make about methanogens is that they were the losers in the race through a bottleneck, yet nonetheless survived in niche environments. Similarly, on a larger scale, it is rare for the loser to disappear completely, or for the latec...
