Elusive Form of Evolution Seen in Spiders
simonsfoundation.org
simonsfoundation.org
When these colonies were transplanted to a new habitat with different pressures, and then their ratio of nannies to warriors was forcibly changed to match the new habitat, the ratio quickly changed back to one that was suited to their old habitat, leading to the death of the colony.
This shows that the colony as a whole evolved to have a certain ratio, and is not merely adapting its ratio on-the-fly (pun intended).
This behaviour in spiders, on the other hand, is highly heritable, so it's definitely linked to a handful of genes, or maybe just one.
Unless, of course, I misunderstand what is claimed. (As always for me, very possible.)
Which is the whole point of "The Selfish Gene". It's not about individuals; it's about their genes. Genes win when their bearer helps out other individuals sharing the same genes.
It's one of my favourite books, but I wonder if it had much of a lasting influence academically. It seems this article doesn't even touch upon the selfish gene viewpoint.
Aside from a few prominent figures like E.O. Wilson, I believe that gene-level selection is accepted as the norm. And group-level selection has been almost completely out of favor for generations - gene-level selection killed it. That is why this article is interesting, it might show a new shift.
Pruitt and Goodnight don’t propose a mechanism by which the colonies boomeranged back to their original state. And without such a mechanism, some researchers argue that the results could be due to ordinary selection acting on individuals. “I think they over-interpret [the results] as evidence of group-level selection,” said Andy Gardner, a biologist at the University of Oxford. “Natural selection may factor in the needs of the group, to some extent, when it hones the adaptations of individuals. But group fitness is not the whole story.”
I understand Gardner's point to be that even if the selection pressure starts at the group level, it can still go down to the individual, and then down to the gene. In that sense, we're still selecting the gene.
Actually, upon reading the actual article, the authors say basically the same thing in the first paragraph:
"In societies in which individual fitness is tightly linked with the performance of the group, the theory of group selection predicts that evolution will favour traits in individuals that aid in maximizing their group’s success—which, in turn, are predicted to increase individuals’ long-term evolutionary interests. Here we define group selection as selection caused by the differential extinction or proliferation of groups1. This represents a broad definition that is not in any way adversarial to the importance of kinship selection for social evolution."
Assuming I understand the authors correctly, they mean that the "fitness" of an individual cannot always be considered to be in isolation. In order to determine the fitness of an individual, we may have to consider the combination of the individual, and the group in which they live. I see that as consistent with the notion of a "selfish gene", as I understand it.
Obviously many/most? animals have evolved group behaviours that benefit their species over other species which in turn benefits themselves.
Often these behaviours are not directly related to propagating their own genes ie protecting someone else's kid or having enough poison in you to scare something that kills you into not eating others like you.
How are these spiders different?
The 'group' that was suited to the environment failed.
This to me proves that groups don't evolve. If it was the group that evolved and not the individual then the group suited to the environment would have survived.
Instead it reverted back to combined individual behaviour.
The individuals had evolved to their environment and had genetic behaviour that allowed them in their natural environment to work as a team for the success of all members as per usual. Put them into another environment and they fail because their personal evolution was not perfected for that environment.
Is it not just a question of whether evolution could produce specialized one-offs that don't reproduce but do serve a purpose? Wouldn't the significant population of homosexuals be a sign of this? Perhaps a biologist could give some info on why many biologists think this is unlikely?
http://en.wikipedia.org/wiki/Fraternal_birth_order_and_male_...
Biologists do not normally regard it is "altruism" if you give resources to someone who shares at least "50%" of your genes. (The 50% is in quotes because any 2 creatures that belong to the same species will have well over 99% of the same genes, and often 99.9% of the same genes. The "50%" actually refers to only to those genes that vary in your species. Dawkin talks about this, too, in "The Selfish Gene".)
Of course, all other things equal, when you pit groups against each other then group selection will occur. But the problem is that a huge body of science, both theoretical (game theory) and observational, argues that things are not equal: At the same time as the groups are competing, there is in-group competition. There has to be, because the groups consist of organisms that are being selected for, unless someone can propose a mechanism that would suppress that.
What this means is that group selection is unstable. A group behavior might be selected for, but individuals in the successful group will still be selected for "selfishly" - normally - breaking the pattern. If selection operates on the gene level - and almost all biologists believe it does - then it is inherently going to act on a scale much smaller than that of groups, and in an inevitable manner. And that is going to destabilize any group selection.
For these reasons it was thought that altruism couldn't be easily explained through evolution. That's why kin selection, reciprocal alruism, and a few other theories are so revolutionary - they show how useful group behaviors arise from selection at the gene level.
> Is it not just a question of whether evolution could produce specialized one-offs that don't reproduce but do serve a purpose?
That does occur in the "eusocial" animals, such as ants and bees. But it is generally believed that happens due to how genes are passed on in those insects (different than we are used to among mammals), and they are a large exception. In practically every species we are aware of, group-level selection does not occur. Hence any evidence, as in this article, is very interesting.
The whole evolutionary biology field is quite depressing actually. It doesn't seem to make any cumulative progress whatsoever.
http://en.wikipedia.org/wiki/Mutual_Aid:_A_Factor_of_Evoluti...
* How did they change a docile group into an aggressive one? If I understand this correctly, they took a group of, say, 1000 spiders with a ratio of, say, 10-to-1 docile and removed about 890 spiders to create a new 1-to-10 ratio with 110 spiders. But doesn't such a change in group size also change the group itself significantly?
* How was everything tracked after they've been transferred to an environment?
Douglas Adams described it years ago: https://www.youtube.com/watch?v=sCsHuoVABgI