A friend noticed that I am confused about the effects of removing genetic load.
The story I’ve heard being advanced by e.g. Steve Hsu goes like this:
If you remove rare mutations from the genome of an animal (replacing them with the common variants), e.g. everything that less than 1% of other animals in the same species share, you will remove mostly slightly harmful mutations. So, the animal with modal genes would be healthier, stronger and probably more intelligent than the typical animal from that species.
But I’m confused about rare slightly beneficial mutations. Some of them might not be beneficial enough to have reached fixation, so they would be removed as well. Why shouldn’t the effects then cancel out?
I can imagine two answers: First, slightly beneficial mutations are much rarer than slightly harmful mutations, or second, perhaps helpful mutations either reach fixation quickly or disappear quickly, while slightly harmful mutations linger for a long time.
Is any of these two is accurate? Or am I overlooking something crucial?
Might help if you look at fixation as a property of population size. (Different groups that don’t have contact with each other, can vary in size and thus fixation difficulty/speed. Smaller populations have stuff reach fixation faster (positive and negative*).)
*I haven’t heard a lot about interactions between genes, and how ‘positive/negative’ a gene is is a function of what other genes you have (and environment). (For some, what others have is also relevant, and I have heard about one of those.)
Why shouldn’t the effects then cancel out?
This is about a baseline. When you consider that the baseline takes for granted a certain level of performance, then, maybe there are beneficial mutations which are taken for granted now, but took time to develop. (i.e., what a species looks like now, can be very different from what came before, if you go back far. Change can be slow...though, so ‘a long time ago’ might not be as long for, say, flies.)
Both your answers are right. Another reason is that evolution has been operating on the basic human genotype for a very long time and has likely found most of the one gene beneficial mutations and has had time to spread them. But because of copying error evolution is always able to “find” new harmful mutations.
A friend noticed that I am confused about the effects of removing genetic load.
The story I’ve heard being advanced by e.g. Steve Hsu goes like this:
If you remove rare mutations from the genome of an animal (replacing them with the common variants), e.g. everything that less than 1% of other animals in the same species share, you will remove mostly slightly harmful mutations. So, the animal with modal genes would be healthier, stronger and probably more intelligent than the typical animal from that species.
But I’m confused about rare slightly beneficial mutations. Some of them might not be beneficial enough to have reached fixation, so they would be removed as well. Why shouldn’t the effects then cancel out?
I can imagine two answers: First, slightly beneficial mutations are much rarer than slightly harmful mutations, or second, perhaps helpful mutations either reach fixation quickly or disappear quickly, while slightly harmful mutations linger for a long time.
Is any of these two is accurate? Or am I overlooking something crucial?
If you randomly change something in DNA it’s much more likely that something will work less well than that something will work better.
It’s similar to how making random changes to the computer code of a program is going to be harmful in most instances.
Thanks :-)
This was what I was trying to get at in the first possible answer.
Might help if you look at fixation as a property of population size. (Different groups that don’t have contact with each other, can vary in size and thus fixation difficulty/speed. Smaller populations have stuff reach fixation faster (positive and negative*).)
*I haven’t heard a lot about interactions between genes, and how ‘positive/negative’ a gene is is a function of what other genes you have (and environment). (For some, what others have is also relevant, and I have heard about one of those.)
This is about a baseline. When you consider that the baseline takes for granted a certain level of performance, then, maybe there are beneficial mutations which are taken for granted now, but took time to develop. (i.e., what a species looks like now, can be very different from what came before, if you go back far. Change can be slow...though, so ‘a long time ago’ might not be as long for, say, flies.)
Both your answers are right. Another reason is that evolution has been operating on the basic human genotype for a very long time and has likely found most of the one gene beneficial mutations and has had time to spread them. But because of copying error evolution is always able to “find” new harmful mutations.