Sunday, 9 June 2013

'Selfish' Genes Create Cooperative Organisms

Diagram of a generalised plant cell
One of the criticisms of Richard Dawkins' seminal work, and the work which initially made him famous as an evolutionary biologist, The Selfish Gene, is that it portrayed life itself as essentially selfish, so undermining any claim Atheists might have to be moral, empathetic and considerate people. This was of course always nonsense and is an example of attacking a scientific theory based on its consequences not on its validity, as though truth is subject to a human convenience test - rather like claiming nuclear fission doesn't work because atom bombs are destructive or that the Big Bang can't have been an uncaused event because that would shut god(s) out of the picture.

But the consequences of 'selfish' genes are not as is claimed anyway. In fact, anything more than a cursory glance at biology will reveal how cooperation, at all levels of organisation, has almost always been the key to long-term success. Examples of cooperation are alliances of 'selfish' genes to create vehicles for their replication and continuation over time - in other words the things we call organisms and species - the whole of life in fact. It is to the mutual benefit of all these genes to work together - not as a conscious cooperation but merely as a consequence of their 'selfishness'. Quite simply, cooperative alliances are much more likely to be successful in terms of the number of descendants they produce than is competition. In biological terms, that is all that success means.

Alliances are not confined to genes within a single organism, of course. Alliances between organisms are common-place too: Bees and flowering plants, fungi and trees (and several other plants such as orchids), fungi and bacteria in lichens, ants and aphids, humans and domestic animals, etc, etc. These are all examples of alliances of genes in individual species being more successful in cooperation with other alliances of genes in other species. Cooperative alliances are always more stable than predator-prey relationships which lead to the huge overhead of arms races to no one's long-term benefit.

One fascinating alliance that we only really became aware of in 1966, and then only gradually, was the theory of complex cell (eukaryotic) origin proposed by Lynn Margulis, and now widely accepted, that eukaryotic cells are actually alliances of simple (prokaryotic) cells which may have begun as endoparasitic or prey-predator relationships - the Endosymbiotic theory. The former prokaryotic cells are now the organelles in eukaryotic cells, of which all higher life, including multicellular life, is composed.

In a very real sense, we are all alliances of bacteria!

Chloroplasts in Plagiomnium affine. Photo by Kristian Peters
One such organelle, which is now fundamental to plant life, and, through its production of oxygen in the atmosphere, to almost all life barring a few anaerobic bacteria and specialist extremophile organisms clustered around 'black smokers' in deep ocean trenches, is the chloroplast which contains the green pigment in plants and which turns carbon dioxide, water and sunlight into sugar, forming the basic energy source for almost all living things. These are believed to have begun life as free-living bacteria which evolved the ability to photosynthesise sugar to become cyanobacteria, and were then incorporated into algal cells, probably first as ingested food and then as a source of sugar for the algae. It's not hard to imagine how an algal cell which swallowed cyanobacteria for food would quickly evolve to not actually digest it but to let it live and to simply appropriate the surplus sugar. No point in killing the goose that lays the golden eggs!

There was only one snag to this theory: there were no examples of algal cells feeding by ingesting bacteria!

Now, as reported in this week's New Scientist, a team from the National Institute for Basic Biology in Okazaki, Japan, led by Shinichiro Maruyama think they have found one.

The pair studied Cymbomonas, a single-celled alga which belongs to one of the oldest algal groups. Cymbomonas ordinarily survives by photosynthesising, but when they grew it under low light levels it took to eating bacteria (Current Biology, doi.org/mm2).

However, rather than extending a blobby "arm" to engulf its prey like other single-celled organisms, Cymbomonas sucked the bacteria up into a feeding tube. The tube led to a bubble-like chamber called a vacuole, a sort of microscopic stomach where the bacteria were digested. Maruyama says that the first green algae may have taken up their bacterial companions in the same way as Cymbomonas, except they didn't digest them.

Hungry algae may explain how plants became green; Michael Marshall, New Scientist Issue 2920, 06 June 2013.

Cooperative alliances are the single greatest achievement of selfish genes. The entire web of mutually interdependent life on Earth owes its existence to these alliances, even the mutual interdependence of plant and animal life as animals provide the carbon dioxide for plants to use to make the sugars for animals to eat.

The lesson from evolutionary cell biology for evolving and developing human society is that cooperation and inclusion works for the long-term benefit. If we are to have any future we have to learn to cooperate not just with one another and one culture with another but with the entire system of life on this planet.

References:
Hungry algae may explain how plants became green; Michael Marshall, New Scientist Issue 2920, 06 June 2013 (subscription required)

Wikipedia - Endosymbiotic theory





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1 comment :

  1. I love this theory as it gives us the mitochondria. Which in turn gives us mitochondrial DNA which sends creationists all over the planet running for shelter.

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