There is an amazing new series on BBC. Animated by Brian Cox again, called ‘Wonders of Life’. If you can figure out how to get access (within the UK it is available to licence holders, outside of the UK you have to make their servers think you are in the UK. I am not going to tell you how to do that, as it might make me liable for something, but if the initials VPN mean anything to you, you might be able to work out how to do it.)¸In the first episode he talks about (and shows some amazing footage of) an animal that I didn’t know about, a jellyfish that has an intracellular parasite that photosynthesizes. So the jellyfish migrates every day in a reproducible pattern, that leads to the greatest exposure of these parasites to light. They even rotate as they swim so that the largest possible number of parasitic algae are exposed to the light.
We know that one of the crucial steps in the evolution of eukaryotes was the invasion of prokaryotic cells by parasitic organisms that became mitochondria or chloroplasts. I do not have the biology education that I wish I had, so I did not realize that there are many examples of intracellular parasites, similar to what must have happened a few billion years ago in the early evolution of complex life.
You might ask why a physicist is presenting a biology program. I will let Brian Cox himself explain; so go see the programs, if you can.