Humans Are Superorganisms

colonist writes "You are not completely human. You are a superorganism made up of human cells, fungi, bacteria and viruses. That's the view of scientists from Imperial College London and Astra Zeneca, published in Nature Biotechnology. Microbes in the gut can weigh up to one kilogram, forming the second largest metabolic 'organ'. Human cells and genes are outnumbered by microbial cells and genes. 'Understanding the man-microbe interaction is likely to be crucial in realising personalised medicine and healthcare in the future,' says the lead researcher."

Comments

What's new?

[Finuvir]

What's new here? We've known for a long time that eukaryotic cells contain bacteria that do most of the interesting chemical work for us. Chloroplasts in plants are seperate organisms that photosynthesise. Mytochondria, which are so useful in tracing animal lineages, are bacteria inside animal cells that extract energy from sugars and oxygen (they metabolise for us). Termites in Darwin, Australia (known as Darwins termites) don't digest their own food. That's done by prokaryotes in their gut, which themselves are crowded with other tiny critters that do most of their work (propulsion is done by one set of bacteria which are powered by another group).

For an accessible introduction to this kind of symbiosis, see The Ancestor's Tale: A Pilgrimage to the Dawn of Life by Richard Dawkins.

Re:Well

[reverseengineer]

I think the mitochondria argument is in reference to the idea of "endosymbiosis," which suggests that mitochondria (and chloroplasts) were originally independent prokaryotic organisms that were at some stage incorporated into eukaryotic cells, the primary evidence for this being that these organelles have their own DNA. They then became highly specialized at a certain task (aerobic respiration, photosynthesis) and discarded the machinery required for independent survival. The eukaryotic cell benefited by gaining sets of powerful new energy pathways in nice self-contained packages, and the organelles benefited by being passed on whenever eukaryotic organisms reproduced (you have your mother to thank for your mitochondria, as yours descend from the mitochondria of her egg cell). As to whether mitochondria are alive, well, biology has a way of making airtight definitions very difficult- after all, there are plenty of complex species which are completely dependent on other species in order to live and reproduce; we call them parasites.

Now, despite that, I'm personally in the "not an organism" boat, as mitochondria are really not much different from other "opportunistic" pieces of DNA like viruses and plasmids. It just happens that the bag the DNA comes in is extraordinarily useful to the host cell. Indeed, while mitochondria are completely dependent on host cells to reproduce, life on earth would be far different- there'd be no way an ATP-guzzler like the human brain could have evolved without the benefit of aerobic respiration, for instance.

In reference to the whole "humans are superorganisms" idea, one of the things I got from a microbiology course I took in college was the ubiquity of microorganisms on and in the human body- and how their relationship to the host organism can be anything from beneficial to deadly. I think that considering the other billion residents of the body when examining avenues of treatment is a wise move.

Re:Lynn Margulis' Research

[reverseengineer]

Yeah, good point, I was somewhat surprised too. I should have mentioned her in my post, actually- endosymbiosis, which I did mention, is her idea, and along with James Lovelock, so is the Gaia Hypothesis (which admittedly I'm less hot on). The idea of complex organisms as "superorganisms" in symbiosis with their own ecosystem of microbes fits nicely in scale between her two major ideas, one of which is about the relationship between a cell and some of its organelles and the other of which is about the relationship of the entire biosphere to all of its inhabitants.