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Evolution question

dogjones

Graduate Poster
dogjones
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I think this may have been dealt with before, but does evolution as we understand it allow for traits to develop that may lessen the survivability of an individual but overall increase the survivability of a group/species? If so, how would the trait be selected for?

I guess I'm thinking of the whole altruism debate. Alice and Bob both see a stranger about to be run over by a bus. Alice dives in, saves the child and kills herself. Bob doesn't. Doesn't this give Bob-like, non-altruistic traits the obvious edge in terms of selection?
 
Sickle cell trait is a classic example. It's very bad for an individual that gets two copies of the gene but increases resistance to malaria in individuals who inherit one copy.

A trait is "selected" if it makes it to the next generation. It will increase in the population if it leads to more reproduction amongst those that posess the trait. And the details of how it increases reproduction don't matter. If a trait were to kill 50% of the individuals that carry it the second after they are born, but lead to fives time greater reproduction amongst the survivors, it would be selected.
 
Quite many small creatures multiply by the millions, which is bad for the many individuals who are doomed to die, but it ensures the survival of the species, as some of the millions of individuals will always survive.
 
dogjones said:
I think this may have been dealt with before, but does evolution as we understand it allow for traits to develop that may lessen the survivability of an individual but overall increase the survivability of a group/species? If so, how would the trait be selected for?

I guess I'm thinking of the whole altruism debate. Alice and Bob both see a stranger about to be run over by a bus. Alice dives in, saves the child and kills herself. Bob doesn't. Doesn't this give Bob-like, non-altruistic traits the obvious edge in terms of selection?
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Colonial insects, for example. The vast majority of the animals do not reproduce and work themselves to death so that the queen can reproduce.

The colony survives.
 
Without regard to people, ants (and bees) are the ultimate altruistic creatures. One female out of thousands or millions reproduces, while all of the others live a sterile life and die. How would this evolve? It appears that the colonial aspect evolved first, as there are no non-colonial ants (I believe) but there are some primitive ants (bulldog ants) that have fertile workers. These colonies can survive the death of the queen. Once the insects began their social behaviors, eventually there must have been colonies in which the reproductive abilities of the workers were less and less successful without significantly hurting the hive's ability to reproduce. Eventually we wind up with some ants that can breed and the vast majority that cannot. As far as the individual steps go, I don't know, perhaps there's an entomologist out there who knows.
 
dogjones said:
I think this may have been dealt with before, but does evolution as we understand it allow for traits to develop that may lessen the survivability of an individual but overall increase the survivability of a group/species? If so, how would the trait be selected for?

I guess I'm thinking of the whole altruism debate.
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Keep in mind that the key may not necessarily be survivability of the individual, but survivability of the individual's genes. Thus, a parent may be willing to sacrifice themselves for their children, or one sibling may be willing to sacrifice themselves for another sibling (since they share some of the same genes). Back when humans lived in smaller tribes, you'd have a better chance at having some genes in common with other tribe members, even if you weren't directly related. So, saving your neighbour may end up saving a few of your own genes indirectly.

Plus, developing 'altruistic' attitudes may not necessarily provide an immediate benefit; however, they may generate a longer-term benefit; a small group where everyone is altruistic might provide for better survivability of the group (and thus the individual or the individual's relatives). This is kind of like the prisoner's dilema.

Alice and Bob both see a stranger about to be run over by a bus. Alice dives in, saves the child and kills herself. Bob doesn't. Doesn't this give Bob-like, non-altruistic traits the obvious edge in terms of selection?
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There are a couple of possibilities:

- Although the child that Alice saves is a 'stranger', there's still a chance that they have some genes in common. (It would have been more common a few million years ago when humans, or pre-humans, lived in smaller tribes)

- By his lack of action in saving the child, its possible that Bob would be seen as a 'jerk' by others, and thus any potential mates would see him as a less desirable mate
 
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dogjones said:
I think this may have been dealt with before, but does evolution as we understand it allow for traits to develop that may lessen the survivability of an individual but overall increase the survivability of a group/species? If so, how would the trait be selected for?

I guess I'm thinking of the whole altruism debate. Alice and Bob both see a stranger about to be run over by a bus. Alice dives in, saves the child and kills herself. Bob doesn't. Doesn't this give Bob-like, non-altruistic traits the obvious edge in terms of selection?
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Dawkins' book The Selfish Gene addresses this in some detail.

The quick answer is "yes," but there are some subtleties involved. The first subtlety is that your example is too extreme; trading a life for a life is almost never worth it (evolutionarily speaking), but most instances of "altruism" are much more subtle. A better example would be sharing food with a neighbor instead of eating it yourself -- if you fail to eat it, you won't die, but your neighbor might if THEY die. Even trying to pull a child out from under a bus will usually save the child without killing you.

The trick is to look at survival not in terms of individuals, but in terms of genes. In other words, by saving that child, you are also saving all of her genes and allowing them to continue reproducing. If she shares many of your genes -- for example, she is your daughter or close relative -- then (some of ) the genes you are saving are the same as your genes. In other words, you're actually saving "yourself" in some sense.

For most of human history, any human you saw shared a lot of your genes, because of the group/tribe structure we inherited from the rest of the primates. Not so much any more, but our genes haven't really had time to dissociate themselves from roving bands of hunter-gatherers on the savannah.
 
dogjones said:
I think this may have been dealt with before, but does evolution as we understand it allow for traits to develop that may lessen the survivability of an individual but overall increase the survivability of a group/species? If so, how would the trait be selected for?

I guess I'm thinking of the whole altruism debate. Alice and Bob both see a stranger about to be run over by a bus. Alice dives in, saves the child and kills herself. Bob doesn't. Doesn't this give Bob-like, non-altruistic traits the obvious edge in terms of selection?
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evolution is genetic, not cerebral
;)
 
I found this article with a Google search for evolution altruism. It provides a thorough discussion of the subject but is too long to summarize here. It makes use of several different animal examples but mainly refers to Vervet monkeys who give alarm calls to warn fellow monkeys of the presence of predators, even though in doing so they attract attention to themselves, increasing their personal chance of being attacked.
 
Marduk said:
evolution is genetic, not cerebral
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Because, of course, no behavior has any basis in biology whatsoever.

Of course, in the reality-influenced world, "evolutionary psychology" is an active research field studying exactly how evolution affects thought and behavior.
 
I second the recommendation of reading The Selfish Gene, by Richard Dawkins (2nd Edition or later).

Altruism can actually emerge from units that individually act "selfish", when they discover that they can best suit their own needs by working well with others.

Some genes may sacrifice one individual if they "know" they can save many other copies of themselves, at least at a rough estimate.

It helps if you share two thirds of your genome with someone (instead of the typical 50% given to an offspring), as is the case with social insects.
 
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Wowbagger said:
I second the recommendation of reading The Selfish Gene, by Richard Dawkins (2nd Edition or later).
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The Selfish Gene is excellent and reasonably accessible. The Extended Phenotype is a better book, but depending upon your level of background knowledge, you may not find yourself able to get through it.

Linda
 
fls said:
The Selfish Gene is excellent and reasonably accessible. The Extended Phenotype is a better book, but depending upon your level of background knowledge, you may not find yourself able to get through it.
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True that. But, even so: I would say The Selfish Gene should be considered pre-requisite reading for The Extended Phenotype.
 
If the child Alice saves is her (and Bob's) daughter, then half Alice's genes - and half Bob's- survive.
So on balance, it's better to push your spouse under a bus than your kid.
 
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