Modern medicine has made normal life possible for many people who would otherwise have died before they were able to reproduce. Consider those people who have a severe allergy to peanuts, and carry around epinephrine in the event that they accidentally contact something with peanuts in it. Or those who have a congenital heart defect that needs to be repaired by surgery. Or juvenile diabetes. And so forth.
Historically, I’d assume the fact that these diseases would normally kill their sufferers before adulthood limited their spread throughout the population. But in the past 100 years, modern medicine has meant that these diseases are not fatal, if treated or dealt with properly. And so, their sufferers are free to survive long enough to have children of their own, potentially passing on whatever genes may have contributed to their diseases.
Does this mean that, for the foreseeable future, an ever-growing fraction of children in the developed world will be born with these congenital diseases that need to be corrected or dealt with by medicine? Now that natural selection has been bypassed by medicine, is the human race destined to become progressively physical weaker, and continuously more dependent on our collective intelligence to keep us alive?
generally speaking, you’re right on, but I’ll add that genetic therapies, though still in its infancy, has the potential to get rid of the problem you mentioned
The medical advances that have made it possible for people with genetically determined illnesses to survive long enough to have children, have also made it possible to screen for genetic problems, both before and after birth. More choice is available on whether to risk having children with severe defects.
If you examined populations from different eras, would current ones really be sicklier? If you look into, for example, men entering military service in the WWI era and compared them to incoming servicemen now, I’d bet the current crop are much more physically impressive specimens.
Seems that advances in medical care and nutrition have outweighed whatever drain on our “genetic heritage” has occurred.
What does it matter whether our ability to deal with certain diseases comes from our genes or from medicine or from whatever else? Whatever the path, we still end up able to deal with the disease.
So, yes, perhaps we are becoming dependent on medicine, in the sense that medicine is giving us benefits we would rather not forgo. But why describe this as humanity’s health suffering? It seems to be aptly described as a good thing from the perspective of humanity’s health, even if the same good effect could perhaps be alternatively achieved, in the long run, by letting people today suffer in order to merely evolve back to the current level of ability to deal with disease. There’s no advantage to the evolutionary path over the medical path, and giving up the latter for the former just has the disadvantage of causing needless suffering now.
The intelligence that creates the technology that enables people to live longer, healthier lives is part of our evolution. In and of itself, it is as significant for our collective survival as the first sea creature to step foot on land.
I think you’re applying a modern definition of ‘adulthood’ to a very different historical one.
Currently, we consider ‘adulthood’ to begin at age 18 or 21.
But through much of history, people were married and reproducing much earlier – very soon after puberty. Often ages 13-15. Romeo & Juliet, for example, were 15 & 14 when married.
So while these diseases might kill their sufferers before what we would consider adulthood, quite possibly they will have already produced children (and thus passed on their genetic heritage) before then.
There are several reasons to think that there won’t be any tendency for people to more often have debilitating physical conditions in the future than there is in the present. The first is the analogy with the supposed tendency toward lowered intelligence because people with a lower I.Q. breed more than those with a higher I.Q. People who believe this is the case have calculated that the average I.Q. should drop by about one point per 30 years, given the differential between the number of children people with a lower I.Q. have compared to the number of children that those with a higher I.Q. have. (Actually, they don’t even know precisely the differential between these two numbers, since they can only calculate it indirectly. There aren’t any large databases correlating the number of children with the parents’ I.Q. What exists are databases correlating the number of children with the parents’ income. There are also databases comparing people’s income with their I.Q. Indirectly then one can calculate the differential in number of children with the I.Q. of the parents.)
The problem is that we now have 80 years of experience in giving I.Q. tests to large populations, and we know that the average I.Q. has been rising by about 9 points every 30 years. This is the Flynn effect:
So even if there is a tendency for less intelligent people to breed more, it’s completely swamped by some environmental factor which is increasing whatever I.Q. tests are measuring.
Look at allergies, which is one of the examples you cited in your OP. Allergies are apparently increasing because of an environmental cause:
It appears (although it hasn’t been definitively proven) that the increase in allergies recently is because our environment has less parasites, so children’s immune systems aren’t making the accomodations to them that they used to make. So this is another example where environmental factors are swamping genetic ones.
I think that people who believe that physical weaknesses are being bred into the human race because of our better medical treatments are implicitly assuming the following: In the past, most people were superb physical specimens. The few who weren’t almost always died young because they got no medical treatment. They hardly ever had children, so their conditions weren’t passed on to later generations.
I suspect that that’s completely wrong. I suspect that the various sorts of physical weaknesses were just as common then as they are now, and there wasn’t much of a tendency for such people to have less children. Having physical problems was considered to be not even much of a thing to notice. People were often sick with diseases with a genetic cause, and the people around them would just say, “Well, that’s how life is. Most of us can expect to be sick for significant portions of our lives. Most of us will die fairly young. There’s nothing to be done about it.”
Probably. But we’ll also probably be able to screen for or eliminate those genes. We already do the former to a certain extent.
Not really. We’re not losing any of our genetic diversity, and as long as there isn’t any selective pressure for those genetic diseases, there is no reason to think they will become predominantly represented in the general population.
If a natural disaster wiped out our technology base, and were effectively thrust back 10,000 years, there is no reason to think that we’d have less genetic diversity than we had 10,000 years ago. Certain genetic traits would be selected for, and certain ones would be selected against, and we’d almost certainly find our way back to civilization (assuming the environment wasn’t completely devastated, and we could begin farming again).
The other very important thing to consider is that deleterious recessive alleles are present in the population at much, much higher frequencies than they are expressed.
Suppose one person in 100 is a carrier for the disease. That means that on average, that person will mate with another carrier only 1 in 100 times. So the frequency of carrier-carrier matings is not .01, but rather .01 * .01, or .0001, or one in ten thousand. And out of those matings, only 1 in 4 of the children will actually have two copies of the bad allele, so even a very common genetic disease carried by 1% of the population will only be expressed in 1 out of 40 thousand individuals.
Now, suppose that the genetic disease is so severe that it is guaranteed that anyone afflicted will die before reproductive age. But the selective pressure against this gene is very very small. Only a few people actually have the disease and die from it, but lots and lots of people carry it. The increase in frequency of the allele in the next generation due to this one homozygous individual not dying is very very small. And note that the rarer the genetic disease is, the less impact removing that one person will have, because very rare genetic diseases are almost never expressed, because the frequency of expression is the square if the frequency of the allele.
If you really want to remove the allele from the population, letting the affected individual live or die is pretty much irrelevant. You’ve got to kill off the carriers. And the trouble with this is that almost everyone is a carrier for some genetic disease or another, we just never know it because the odds of reproducing with another carrier of that exact genetic disease is very low. Of course, these odds increase when you don’t mate at random, but instead mate with related people. Your relatives are more likely to share the same deleterious recessives, and this is why isolated populations tend to express genetic diseases more frequently…not because they carry more genetic disease, but because they are more likely to reproduce with another carrier of the same disease.
So selection against the affected individuals has very little effect on keeping frequency of the allele low. Killing the affected individuals won’t keep the gene pool clean, because the affected individuals are only a tiny tiny fraction of the people who have the allele.
Lemur866 said what I would have said in Tarzan speak : Type I Diabetes runs in families and the actual sufferers aren’t/weren’t the only carriers - it doesn’t really matter much that they personally have offspring or not (much) as long as they have brothers, sisters, cousins etc. that will carry the gens into the future - that is true of almost any genetic disease you care to mention.
Hijacking this ‘cos this is one of the subjects I can’t resist posting about: Juliet is indeed not quite fourteen at the time the play takes place; however, this was not the age at which non-aristocratic Elizabethans typically married. Shakespeare stresses R&J’s extreme youth in order to heighten the pathos and emphasize the degree to which the protagonists are victims of their parents’ schemes.
The average age of marriage in Elizabethan England was not much lower than it is in contemporary America – about 23 to 24 for women, 25 or 26 for men. In general, people needed that time to finish their apprenticeships and save up enough money to support a household. Obviously, among the royalty and aristocracy, these financial concerns didn’t apply, and teenagers could be and were married off at a very young age to cement political alliances. But as a rule, people did not marry at or immediately after puberty.