Doug S, G has given a good explanation (except possibly the last sentence which is debatable.) I’ll explain again: Selection happens when genes increase in frequency compared to other genes. Since genes always happen inside individuals, a gene that causes its individuals to leave fewer offspring in the population will be selected against, regardless of what it does for the population as a whole.
A gene that results in good stuff for the population but that doesn’t result in its own carriers increasing more than others won’t increase in the population even though all the individuals in the population would be better off.
You can get by this a little by assuming a population split into breeding groups with limited outbreeding, where a gene that improves the group enough can take over in a small group, and then when the group gets bigger it splits and both groups increase compared to other groups, etc. But too much outbreeding would stop it. Something like this may happen in rats and fruit flies etc, too soon to be sure.
There could be specific genetic mechanisms that provide a system to to create group selection. Diploidy is a peculiar genetic mechanism, as are sexuality and dominance. There could be others that are less obvious, that benefit the populations that let them operate, and group selection is one of the things they might promote. But that’s entirely speculative at this point.
Doug S, G has given a good explanation (except possibly the last sentence which is debatable.) I’ll explain again: Selection happens when genes increase in frequency compared to other genes. Since genes always happen inside individuals, a gene that causes its individuals to leave fewer offspring in the population will be selected against, regardless of what it does for the population as a whole.
A gene that results in good stuff for the population but that doesn’t result in its own carriers increasing more than others won’t increase in the population even though all the individuals in the population would be better off.
You can get by this a little by assuming a population split into breeding groups with limited outbreeding, where a gene that improves the group enough can take over in a small group, and then when the group gets bigger it splits and both groups increase compared to other groups, etc. But too much outbreeding would stop it. Something like this may happen in rats and fruit flies etc, too soon to be sure.
There could be specific genetic mechanisms that provide a system to to create group selection. Diploidy is a peculiar genetic mechanism, as are sexuality and dominance. There could be others that are less obvious, that benefit the populations that let them operate, and group selection is one of the things they might promote. But that’s entirely speculative at this point.