Has modern medicine halted human evolution?

[SCRawl]

Ok, first off I know the timescales involved in evolution, that things affecting two or thre generations won't change much long-term, but run with me on this.

Now, please note this is based on my understanding of evolution and natural selection. I am not a biologist (I'm an astronomer/accountant by training) so I may well be rusty on the details.

So, here it goes:

Evolution is determined, very simply, by the strong surviving and the weak dying, or rather, that those with sound genes will survive to procreate and those with flaws or defects will not. So, an intelligent, physically strong person will pass on their genes whilst someone who has some genetic flaw will not, so that flaw will not begin to propagate through the gene pool.

But, modern medical science has reached the point where those with genetic flaws do survive to procreate. My own family is a case in point; my father carried the genes for glaucoma, which he passed on to me. Thanks to medical science I retain a modicum of sight and am not completely blind and disabled, so I will, in all probability, be able to pass on said genes to my children. My best friends are further examples: one has spino buffidia (I think that's what it is anyway, he doens't talk about it much) but thanks to a surgery soon after he was born, he has survived to adulthood. My other best friend suffers from a couple of inherited thyroid conditions, but they are kept in check by pills and can be passed on to her kids.

So, it seems from my vantage point that medical science allows genetic flaws and defects to continue to exist in the human gene pool, rather than being bred out as natural selection might suggest.

Does this mean that medical science has halted, temporarily, human evolution? Or am I missing some important factor here?

[Borgholio]

We are allowing those with physical defects to live longer and pass on their genes. IMO, this means traits other than simple physical fitness will become dominant as time goes on. As an example, look at Stephen Hawking. He would be lion-food if left up to nature....and yet he is probably the smartest human who ever lived. Modern science has allowed his massive intellect to survive and help advance the species as a whole, despite his physical handicap. So evolution is taking place in spite of modern medicine...it's just taking a different path.

[General Zod]

It seems to me like this just changes the environmental pressures for selection. It doesn't eliminate them.

[Simon_Jester]

The biggest pressure is, I suspect, for subconscious desire to have kids, as opposed to just having sex. Contraception hugely changes the rules of Darwinian pressure on sexual selection.

Consider that it's only been for roughly two generations in the developed world, and zero to one generation outside of it, that people could realistically decide to not have offspring, except by basically deciding not to have a family or sexual life of any kind.

If there were a single gene that would cause the bearer to decide of their own 'free will' to have, on average, let's say 0.5 more children than would be had without the gene... a few centuries from now practically the entire human race would have that gene. Because in each successive generation, the couples with that gene will be having, say, 2.25 kids while the ones without it have 1.75.

Obviously it's not that simple, but I think this comic pretty much nailed it...

[Alyrium Denryle]

Does this mean that medical science has halted, temporarily, human evolution? Or am I missing some important factor here?

Yeah. You are.

Cognition does not simply depend on brain growth (which is limited primarily by the size of a woman's pelvic girdle and thus birth canal), but on the structure and cognitive processes of the brain.

Subconscious desire to have children? Selected for.
Refinements to the cognitive heuristics we use to process and understand the world better? Selected for.
Mate selection based on social and economic criteria important for child rearing? Selected for.

Our immune systems are constantly evolving even with modern medicine, and people with severe defects might survive, but they dont usually reproduce.

[Broomstick]

Evolution is determined, very simply, by the strong surviving and the weak dying, or rather, that those with sound genes will survive to procreate and those with flaws or defects will not.

Incorrect. Evolution is determined by those who manage to reproduce, regardless of other criteria. If a physically weak specimen nonetheless manages to leave more offspring behind than a physically strong specimen then weakness is selected for (or at least not too strongly against).

This is probably why human are weaker than other primates when accounting for size differences. General cleverness, manual dexterity, and communication skills started to have more impact on reproductive success than brute strength alone.

Those with “flawed” genes may have other more beneficial genes that allow them to be selected for reproduction, thus perpetrating “bad” genes along with “good” ones.

My best friends are further examples: one has spino buffidia (I think that's what it is anyway, he doens't talk about it much) but thanks to a surgery soon after he was born, he has survived to adulthood.

[nitpick] Spina bfidia is NOT a genetic disorder. It is most strongly linked to a folic acid deficiency/general malnutrition in the mother although it can and does still occur in the offspring of women with adequate nutrition. It's an error of development, not of genes, and is not passed on to subsequent offspring. [/nitpick]

So, it seems from my vantage point that medical science allows genetic flaws and defects to continue to exist in the human gene pool, rather than being bred out as natural selection might suggest.

Any flaw that does not kill you or render you sterile prior to reproduction will not be eliminated by natural selection.

Defects that do not manifest until after the typical age of reproduction might not be selected against at all, and if prior to lethality/sterility they confer some sort of benefit they might even be selected for rather than against. An example might be the hemachromatosis gene, which results (in a modern context) in too much iron being absorbed from the diet and slowly poisoning the body. In an iron-poor environment, or one where iron is often depleted from the body (intestinal parasite load, perhaps) this gene might actually be an advantage, particularly for women of child-bearing age. Even in an iron-heavy environment, though, it is unlikely to kill before the mid-40's, allowing ample time for those with the gene to reproduce.

Does this mean that medical science has halted, temporarily, human evolution? Or am I missing some important factor here?

All medical science has done is change the environment.

Some genes that used to be invisible to selection are now affecting reproduction due to increased lifespans making people more aware of them. Others that used to be an advantage may have become neutral or even a disadvantage.

Evolution never stops.

[Eleas]

Any flaw that does not kill you or render you sterile prior to reproduction will not be eliminated by natural selection.

That's not the whole story, I don't think. There should be numerous secondary benefits of, for instance, parents living long enough to protect their offspring and having an inclination toward imparting knowledge that would allow a child to thrive.

[Broomstick]

True, however, traditional societies usually have uncles, aunts, and others acting as back up, and an orphaned child with close living relatives usually has the chance to grow up to reproductive age. Those aren't (usually) as good as full parents but humans do practice adoption, both of relatives and even complete strangers.

[Eleas]

Yeah, that's valid. That's also selected for, though, and since such an extended family unit often shares genetic material, that also means that there's evolution in action.

TL;DR: Natural selection sometimes gets surprisingly convoluted.

[biostem]

My concern is if and when we get to the point where traits can be wholly selected for, said traits that are desirable now may be detrimental or less useful later on. However, once we do have the ability to select traits for the yet-to-be-born, it may not be too far until we can adjust traits of those who are already born as well, so we can simply modify our genome as needed.

[Eternal_Freedom]

OK, thanks everyone, that's quite reassuring. This is what happens when I'm sat around with nothing to do and no-one to talk to, my brain dreams up random questions. Like I said, I'm not a biologist.

[Knife]

Evolution is determined, very simply, by the strong surviving and the weak dying, or rather, that those with sound genes will survive to procreate and those with flaws or defects will not.

Incorrect. Evolution is determined by those who manage to reproduce, regardless of other criteria. If a physically weak specimen nonetheless manages to leave more offspring behind than a physically strong specimen then weakness is selected for (or at least not too strongly against).

To boot, has to do with traits that may help a critter survive and procreate over a trait that doesn't. Keeping in mind that any trait may or may not be beneficial depending on other factors, such as environment. So, a trait that helped a predator eat small critters when all the big ones died off helps but could end up hurting that same predator some thousand generations later when all the small critters die out.

Some of the things that modern medicine are 'allowing' to stay in the gene pool now, may actually be a benefit later. Or not.

[Ziggy Stardust]

A bit of a side note, but an article you may be interested in reading is this one.

It doesn't strictly address your question, really, but I think it is an important concept to understand. From an evolutionary perspective, our relationship with "disease" (and thus medicine) is a lot more complicated than simply "well, disease=bad so healthy people pass on genes". Usually I'd provide a summary or at least useful quotes, but I've had an extremely long day and don't have the energy at the moment.

[Lord of the Abyss]

So, it seems from my vantage point that medical science allows genetic flaws and defects to continue to exist in the human gene pool, rather than being bred out as natural selection might suggest.

Does this mean that medical science has halted, temporarily, human evolution? Or am I missing some important factor here?

Besides what others have mentioned, the time factor. Modern medicine hasn't been around long enough to have a significant effect, or stayed the same long enough to have a consistent effect. Evolution works on a time scale of generations, and it wasn't so long ago on that time scale that medicine was so bad that it was basically rolling dice whether doctors would make things worse or better if you went to them. And medical practice changes on a time scale of years, not generations; so it isn't applying a consistent selection effect.

And before modern medicine is around long enough to have much effect we are almost certainly going to start eliminating genetic defects by genetic engineering; so there's not going to be enough time in the future for natural selection to do much either.

[Broomstick]

I just hope that genetic engineering doesn't bring us new and exciting genetic defects. After all, anyone can make an oops.

[cosmicalstorm]

If* medical technology is allowed to progress it seems obvious we will have full control over biology in a century or so. It could happen much faster but the current paradigm is to try and fix biological damage very late in the process and make a ton of money while doing it. Having full functional control over our brain and genes should make for some interesting things, I doubt the current "problem" with evolution caused by contraception and morons getting paid to have moron kids will be a big problem later on.

*No carrington-events, AI-doom, nuclear war comes to stop us.

[Darth Flesh]

I was about to mention exactly that.
We're probably less than a century away from removing all current genetic flaws and creating all new kinds.

While I certainly look forward to becoming a transhuman, it seems to me that if the economic model continues, anyone who has been engineered with company nanobots would probably find themselves under their illicit control.

Religion has proven to be the best tool for politicians, and through them, corporations to control the uneducated masses.

[Ziggy Stardust]

We're probably less than a century away from removing all current genetic flaws and creating all new kinds.

It's highly unlikely we will ever remove "all current genetic flaws" regardless of our technological level or understanding of genetic mechanisms. The key is that the phrase "genetic flaw" is incredibly vague, the point of being almost meaningless. Our genetic code is not a series of binary states, where something is either "broken" or "fixed". Not only are the patterns of genetic expression that lead to certain traits incredibly complex, but there isn't even a solid criterion of what would constitute a flaw in that system. Many things that can be considered flaws in one context are actually beneficial in order (see: sickle cell anemia). Hell, there's some evidence that the genetic underpinnings of things like creativity and artistry are actually the result of "flawed" mechanisms (meaning atypical with respect to the rest of the population). And this isn't even getting into all of the "flaws" that can occur over the course of a person's lifetime; genetics is not predestination, after all (there's a reason that the genetic codes of identical twins may be the same at birth, but significantly different at 80). There are some genetic traits that are beneficial during youth but become "flaws" at old age (and vice versa). Just as there probably will never be a cure for cancer in the traditional sense of the word; saying otherwise belies a deep misunderstanding of the concepts in question.

Now, I can certainly foresee a not-too-distant-future where we've eliminated all of the more severe genetic conditions caused by, for example, recombination errors and the like (Down's syndrome, et al). And that is certainly what most people in this thread and elsewhere think when they say "removing all current genetic flaws", etc. Most likely, as our understanding of genetics becomes increasingly sophisticated, we will simply better understand the contexts in which certain traits may be beneficial or detrimental, which will effect the way we live our lives, supplemental to things like personalized medicine, etc.

[Simon_Jester]

While I certainly look forward to becoming a transhuman, it seems to me that if the economic model continues, anyone who has been engineered with company nanobots would probably find themselves under their illicit control.

Personally I question this.

Corporations are, in effect, alien hive minds... but they are in that same sense a kind of being. They pursue growth, profitability, and pain avoidance, and legal troubles are a form of pain, even if they can somehow be made to "go away." Successful corporations (as opposed to fly-by-night operations) don't run by scheming to take over the world; they operate within a basically recognizable framework of rules. Changing the rules is disruptive and rocks the boat.

So designing your company's medical technology with dangerous software backdoors to allow you to mind-control people is exactly the kind of thing any corporate executive in their right mind would NOT do. There are other related dangers; that's not one of them.

Religion has proven to be the best tool for politicians, and through them, corporations to control the uneducated masses.

Bullshit. Religion is a terrible tool for controlling First World populations; it works like a charm on about 30% of them (exact amount varies from nation to nation), but lots of people just don't follow the tenets of the local religions, even the ones who say they follow it.

Among the many other tools that are more effective at social control in the First World (and which corporations, sensibly, use heavily):
-Advertising
-Ambition for future wealth (can be used to get poor people to vote against their own interests!)
-Stress-induced apathy
-Fear of the 'foreign' or 'unfamiliar' replacing that which is 'native' and 'familiar.'

There are others, but I can't think of more off the top of my head. Religion is well down the list.

[Starglider]

So designing your company's medical technology with dangerous software backdoors to allow you to mind-control people is exactly the kind of thing any corporate executive in their right mind would NOT do. There are other related dangers; that's not one of them.

Government security & intelligence organisations would absolutely want that capability though, 'to prevent terrorism and protect stability' and current precedent indicates that companies would absolutely comply with government demands for such backdoors. Even if activists manage to prevent it in a few of the more liberal countries, it would still happen in the more oppresive countries.

[Flagg]

Actually, isn't the right population size a determining factor in evolution's "speed".

[Simon_Jester]

Making brain-altering nanotech into a hackable tool that can be used by the state to puppet someone sounds like a very good way to ensure that brain-altering nanotech spreads slowly and that a lot of the early adopters live to regret having done so.