Derek, Japan asked:
Over the past 100 years, and much more so in the past 40 years, medical science has been able to save an increasing number of babies (and mothers) being born that would have not survived if they had been born at any other time in human history. Complications that would have either ended the pregnancy, killed the baby during childbirth, and/or killed the mother are now easily overcome. Is this reducing the quality of the entire human race's gene pool? Due to medical science, the strongest are no longer the only ones to survive today. It seems to me like almost everyone I know has some type of health issue. Is this due to our "diluting" of the gene pool, and is it going to get worse as medical science gets better?
We put this question to Professor Bill Amos, from the Department of Zoology at Cambridge University...
Bill - This is an interesting question but I'm afraid many of the aspects really are quite unresolved.
Perhaps we could start with the problems with births. Humans of course have been evolving larger and larger brains for a while now which gives them larger skulls and this of course can present problems during the birth process. These days, we can use caesarean section but the key point here is that it’s only going to become an increasing problem if those children born by caesarean section are born, grow up and have larger families than on average.
This is a recurrent theme, so for example individuals with spina bifida – this is a rare genetic disease. If they also grow up, again, this is only going to become an increasing problem if they themselves then have larger families, and it’s almost certainly not the case that this would happen with most genetic defects.
I think perhaps more interesting is the question of the immune function, that genes that help us fight disease. And here, I think there may be an interesting issue. In developing countries where there's much less access to medical treatment and antibiotics, many children die through infections that are potentially preventable. This, in theory, removes some of those individuals with weaker or poorly attuned immune systems from the population, but in the western culture where more medicine is present, these individuals would grow up. So what happens to them in western culture? My best guess is that these are the people who are likely most prone to asthma and allergies since these are potentially reflections of a poorly tuned immune system and that is what we might predict these have.
Diana - So modern medicine might change who lives and who dies, but as the human population is so large, the overall effect on the gene pool shouldn’t be species altering and this is because the number of people either being born by caesarean section or surviving in spite of inherited diseases aren’t likely to breed in greater numbers than the rest of the population. Human immune function however may change through time.
Excellent question, and something I often have wondered myself. I look forward to reading the "answer".
While individuals with a given genetic defect wouldn’t be actively selected for, wouldn’t spontaneous random mutations tend to deteriorate functional genes over time in the absence of selective disadvantage to genetic defects?
I somewhat disagree with the stated answer. Looking at genetic disease statistically, many are becoming manageable and offsetting what was in the past a certain death sentence. Some diseases such as sickle cell, Huntington's, and FH are statistically significant and are becoming increasingly manageable. Not to mention if the future of medicine provides increased relief, you could certainly see the retention of genes that otherwise would be eliminated by early death. The Penguin, Tue, 18th Oct 2011
Sickle Cell disease is a somewhat unique disease.
You could take this a step further and ask the question what external factors might effect the human gene pool.