how do organisms evolve genetically into colony organisms?

[charles brough]

A number of animals such as ants, jellyfish, sponges, slime mold slugs and even we humans are multicellular colonies or live as social groups. Is that explained through genetic evolution? How?

 

 

[LawfulBlade]

We don't really need evolution for group formation, per se. Chance alone is sufficient to explain aggregation. Keep in mind, individual drops of oil will aggregate spontaneously into a micelle if they happen to bump into each other, and they have no brain, or capacity to evolve at all. Additionally, groups may form for external reasons where the individual members don't really benefit at all, and would "prefer", if given a choice, not to be in a group at all. A single tree in a forest is an example of this. (Please keep in mind, I'm not a plant biologist.) The forest has sprung up due to a combination of appropriate growing conditions and how far seed gets spread. Competing for soil space and sunlight doesn't benefit a tree, however. The group appears in this case to exist as a detriment to its members. If it's (evolution, now) needed at all, it's needed for retention of group. What's the benefit of remaining in a group?

 

The near-necessity of group living for anything that reproduces sexually is obvious: it requires a willing partner (or third party, with plants) of the opposite sex in order to exist. Furthermore, that means that there needs to be exposure to the opposite sex at appropriate times. Depending on the frequency of ovulation that exposure may just be annually, or it may be constant. If the offspring are dependent upon the parent, need for a nuclear group (at least) is immediate. But in general, weakness in an individual unit, or reliance upon a group to survive is sufficient to explain group existence. Emergent properties of group existence are sufficient to explain the retention of a group, even if it formed by chance alone, and even if reliance doesn't factor into the equation.

 

I'm not sure it makes sense to view these broad things in terms of evolution, when chance is sufficient to explain their occurrence and immediate benefit is present to sustain it. And, I hate to say it, but you'll need to define what you're willing to consider as a group if you want to think about this further.

[CharonY]

Short answer, one of the major mechanisms in social evolution appears to be kin selection (read up on that as well as Hamilton's rule to get a rough idea). There are certain elements that are extremely tricky (most notably the threat of cheaters).

There is a whole branch of evolutionary biologists that focuses on this particular area. Sex is an extremely bad example as it actually is a case against collaboration. It is associated with the famous two-fold cost as opposed to non-sexual reproduction and models using the increase of allelic variance have not been able to resolve this problem. Other, more molecular oriented explanations appear to be more reasonable, but I am not sure if it has been shown mathematically to be a viable solution.

[charles brough]

We don't really need evolution for group formation, per se. Chance alone is sufficient to explain aggregation. Keep in mind, individual drops of oil will aggregate spontaneously into a micelle if they happen to bump into each other, and they have no brain, or capacity to evolve at all. Additionally, groups may form for external reasons where the individual members don't really benefit at all, and would "prefer", if given a choice, not to be in a group at all. A single tree in a forest is an example of this. (Please keep in mind, I'm not a plant biologist.) The forest has sprung up due to a combination of appropriate growing conditions and how far seed gets spread. Competing for soil space and sunlight doesn't benefit a tree, however. The group appears in this case to exist as a detriment to its members. If it's (evolution, now) needed at all, it's needed for retention of group. What's the benefit of remaining in a group?

 

The near-necessity of group living for anything that reproduces sexually is obvious: it requires a willing partner (or third party, with plants) of the opposite sex in order to exist. Furthermore, that means that there needs to be exposure to the opposite sex at appropriate times. Depending on the frequency of ovulation that exposure may just be annually, or it may be constant. If the offspring are dependent upon the parent, need for a nuclear group (at least) is immediate. But in general, weakness in an individual unit, or reliance upon a group to survive is sufficient to explain group existence. Emergent properties of group existence are sufficient to explain the retention of a group, even if it formed by chance alone, and even if reliance doesn't factor into the equation.

 

I'm not sure it makes sense to view these broad things in terms of evolution, when chance is sufficient to explain their occurrence and immediate benefit is present to sustain it. And, I hate to say it, but you'll need to define what you're willing to consider as a group if you want to think about this further.

 

I find it hard to figure it is chance that causes amoeba to swarm together and form slugs that

move out of the water to land and form into upright stalks which, when brushed by passing animals, enable amoebas to reach other bodies of water. Jelly fish are composite animals made up of groups of different animal organisms. They do not do this by choice but because it is innate or instinctive and doesn't that mean it had to evolve that way?

[CharonY]

As I said in my earlier reply, there are whole disciplines dedicated to this particular question. It is quite a non-trivial process. And no, it is not explainable outside the framework of evolution in general and social evolution in particular.

 

Note that cellular behavior is the consequence of the working of their regulatory networks. I would avoid terms like instinctive as much as possible, as it may be misleading in many ways.

Edited October 4, 2011 by CharonY