

Elusive Form of Evolution Seen in Spiders - digital55
http://www.simonsfoundation.org/quanta/20141002-in-social-spiders-evidence-that-groups-evolve/

======
knodi123
TL;DR: Different colonies of these spiders had different ratios of nanny
spiders to warrior spiders, based on the specific pressures of the habitat
they grew up in.

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).

~~~
taeric
I'm somewhat frightened by what this could imply about our cultures. :(

~~~
a_bonobo
Nothing? Cultures are complicated things that may or may not be influenced by
our genetic makeups. The life and death of culture involves thousands if not
tens of thousands of factors, you don't directly inherit your parents'
culture, you have to learn it first.

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.

~~~
taeric
Right, it could certainly be nothing. Which would be among the better things
it implies. It could also be that changing the "makeup" of a society that is
heavy in aggressors is not something that can be done.

Unless, of course, I misunderstand what is claimed. (As always for me, very
possible.)

------
gyom
_The spiders present a puzzle to evolutionary biologists. According to
ordinary Darwinian natural selection, only the fittest individuals will pass
on their genes. But if that’s the case, why do tangle-web spiders act in ways
that might conflict with an individual’s drive to outcompete its neighbors? A
spider that defends the nest might put itself at personal risk, jeopardizing
its chances of producing offspring. And a spider that rears the young might
have to wait to eat until the hunters are sated, so it might go hungry. These
are not behaviors that would be expected to enhance an individual’s fitness._

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.

~~~
pesenti
No, this article does go against the theories in "The Selfish Gene" (which
only predict kin selection). See the whole row between Dawkins and Wilson over
multi-level selection: [http://www.theguardian.com/science/2012/jun/24/battle-
of-the...](http://www.theguardian.com/science/2012/jun/24/battle-of-the-
professors)

~~~
scott_s
To me, the key point of "The Selfish Gene" was that the base unit of evolution
is the gene. I don't see anything in this article which disagrees with this
notion, and they did quote a biologist who said something similar:

 _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.

------
aaron695
This experiment seems to prove the exact opposite to what they are saying.

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.

~~~
SoftwareMaven
A group doesn't "evolve" overnight. That would be environmental pressures
influencing it, not evolutionary. That the groups reverted showed heritability
in the face of individual needs. If it were strictly individual needs, the
colonies shouldn't have reverted; the evolutionary forces that directed
warrior/nanny ratio should have reflected the environment instead of the
ancestry of the group.

------
tokenadult
I'm eager to see biologists who write online regularly about evolutionary
theory comment about this. I've asked Jerry Coyne of _Why Evolution Is True_
to do so by sending him the link. Thanks for sharing the link here; I like
Simons Foundation stories about mathematics, and I wonder whether or not this
finding in biology will hold up.

------
tinco
I've never understood how biologists could argue non-selfish evolution
couldn't be a thing. If you look at groups of organisms as systems, and you
pit the systems against each other, surely eventually the system that evolved
to be superior would win in the end, regardless of whether that means any
subspecies in that group of organisms would evolve to not reproduce?

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?

~~~
azakai
> I've never understood how biologists could argue non-selfish evolution
> couldn't be a thing. If you look at groups of organisms as systems, and you
> pit the systems against each other, surely eventually the system that
> evolved to be superior would win in the end, regardless of whether that
> means any subspecies in that group of organisms would evolve to not
> reproduce?

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.

~~~
jostmey
Well put! Selfless behavior may sometimes evolve, but it is unstable and will
eventually be selected against.

------
m_mueller
They are discussing the results, but I have trouble understanding the methods
and mechanisms.

* 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?

------
bronson
Isn't it well known that natural selection operates on communities? Doesn't
seem very controversial to me.

Douglas Adams described it years ago:
[https://www.youtube.com/watch?v=sCsHuoVABgI](https://www.youtube.com/watch?v=sCsHuoVABgI)

------
drincognito
I'm confused by the subhead. Natural selection occurs at the population level.

~~~
SoftwareMaven
Evolution occurs at the population level, but populations are generally not
thought to evolve.

