Has human evolution stopped?

Factual Questions
1

My knowledge of evolution is that one is “selected against” when one’s genes prevent one from reproducing as a result of an inferiority to being able to cope with one’s environment. Meaning, that a person that is not adapted to their environment would die before they could pass on their genes. Today’s society coddles anyone and everyone, allowing genetic propagation of just about anyone that is able to acheive reproductive status. I believe that genetic retardation might have been eliminated if it had not been for our current standards of “every life is sacred”. I am certainly not in favor of eugenics, but I wonder if our treatment of the ill-equiped is leading to a halt of mankind’s evolutionary progress. I mean no offense to anyone, and have no ill-will toward anyone of any diminished capacity.

This brings up another question, if we are all descended from one person (or at least a very small group of people), then aren’t we all products of incest? Incest has been proven to cause genetic abnormalities, have we just outgrown these obstacles, or does genetic variation promote superior gene selection within a small group.

2

Evolution cannot, does not, and has not stopped.

False, and I think you misunderstand evolution. I like to say it’s not about being perfect, it’s about being good enough. The ‘idea’ is that the fittest will survive, ensuring the survival of the species. If our species has progressed to the point where those with handicaps who in ages past would have died before reproducing are now passing on their genes, that’s a sign that we’re doing fine. That means more people, which means the species gets to last longer.

This DOES sound very cold, like it or not. And anyway, given the high infant/child morality rates people used to have, you figure people who might otherwise have been worthy were killed as well. But for the most part, see above.

No. Incest is defined as sex with someone to whom you are too closely related to be legally married. The vast majority of people are not so closely related that this would be a problem. We’re all very much alike genetically, but usually not so alike that it causes a problem.
You have to understand that incest is illegal because of custom and also because if there is a recessive, harmful trait that runs in a family, incest may increase the likelihood that the offspring will have that trait. That DOES happen even in non-incestuous cases, yes. But the very nature of it is that it doesn’t happen a lot, and even when it does it’s not usually a huge deal, I’d say.

3

I like to say it’s not about being perfect, it’s about being good enough. The ‘idea’ is that the fittest will survive, ensuring the survival of the species. If our species has progressed to the point where those with handicaps who in ages past would have died before reproducing are now passing on their genes, that’s a sign that we’re doing fine. That means more people, which means the species gets to last longer.

Marley, you missunderstand my question. I don’t question our reasons for genetic anomalies, but rather the biological results. BTW, our species can exist only as long as we have a planet to live on, ask any forward thinking astronomer and they’ll tell you that we’re just visiting here.

If I misunderstand evolution, perhaps you would be so kind as to explain it to me.

4

I’m not sure what you’re referring to exactly. The biological result of medicine today is that yes, a greater number of people is surviving. That’s totally in keeping with evolution and does not mean it’s slowed or stopped. You say that in the past, “[A] person that is not adapted to their environment would die before they could pass on their genes.” But if a person - even one with a disability - is able to survive and pass on his/her genes, than he or she IS adapted to the modern environment.

Probably true, but I don’t think it’s relevant to evolution.

I’m talking about one particular aspect of evolution, and I already explained the difference in the way we were looking at it.

5

Evolution cannot, does not, and has not stopped.

Explain extincted species…or site your sources.

Your references seem to be personal, I hope you’re not taking it that way.

“[A] person that is not adapted to their environment would die before they could pass on their genes.” But if a person - even one with a disability - is able to survive and pass on his/her genes, than he or she IS adapted to the modern environment.

Wrong!! This is an example of an environment being adapted to a person, this is what I’m talking about. Society adapting to human behavior circumvents the natural selective processes that nature has imposed. If you think that I’m a fan of eugenics, then you should have read my previous postings, I’m interested in the BIOLOGICAL, not moral, aspects of this issue. Thank you.

6

Don’t forget there are two strands to evolution. The survival of the fittest is one side. but Darwin was keen to highlight a less well known side - sexual selection. The second mechanism comes about because people (rather than survival) chose their mate, thus accounting for such survival absurdities as the peacocks tail. This may be a reason for instance that bra sizes are increasing this century? In any case. sexual selection will ensure that mankind will keep changing.

7

The answer to this question is a massive and resounding “NO”.
Firstly it requires us to ignore the 80%+ of the world’s population that doesn’t have access to adequate healthcare. Immediately this proves the answer can’t be affirmative.

Then you can ask whether evolution has ceased in western societies. The answer must again be ‘No’ because of the huge influx of people from developing nations.

So then we might ask whether evolution might cease in a hypothetical western society where there was no immigration. The answer on this case would still be ‘No’. In fact not only wouldn’t evolution cease, it could well procede faster than at any point in the past.

You need to realise that evolution is driven primarily (some would say exclusively) by differential rates of reproduction. Evolutionary success of the individual is measure din terms of number of mature offspring. In the past humans have tended to reproduce at maximal rates. Partly because of a lack of contraception and largely because children were the only superannuation scheme.

Today people decide how many children to have. The difference between the most fecund and least fecund couples is huge. Some couples are still giving birth to 6+ children. Others are opting to have none. I have no figures to support it, but I suspect this difference would have bee much less pronounced in the past. Couples that gave birth to 6 children rarely had all 6 survive. Almost no couples would have had no children at all. Today those couples that choose to have 6 children can be almost certain all will survive. Simultaneously we have large numbers of volountarily sterile or single child couples whose genes are being lost altogether.

How can evolution possibly cease with such a huge difference in reproductive success? Those individuals who are genetically predisposed towards high fertility are more favoured no than ever before, while those that are apathetic towards reproduction are selecting against there own genes.

Any genetic factors that predispose people towards having large numbers of children will multiply at a massive rate, while any that predispose one towards not having young will be weeded out rapidly. This was far less the case in the past.

Rest assured, evolution continues apace, and will do so for so long as any individual produces more children than any other. This is still occurring, and may well be occurring at a faster rate than ever before.

8

It’s just a matter of degree. Our evolutionary ancestors of 200k yrs ago probably brought food to members of the group that were temporarily too sick to hunt or get food on their own. We just do this a lot better today. That is one of our survival strategies as a species.

Not incest, but pretty close inbreeding. No anthropoligist or geneticist will say that we are decended from one (well, it’d have to be two) person. It is thought that we went thru what is know as an “evollutionary bottleneck” about 60k yrs ago. At that time, it is estimated that their were perhaps no more than 10k Homo sapiens in existence. This is the reason we are all so genetically similar today. You can find more genetic variation in chimps who live in a one mile radius than you’d find between humans who live on different contintents.

9

This was the first question I posted to alt.fan.cecil-adams, many years ago, long before this board even existed, and I was lambasted for even asking. Thankfully people are more polite now.

Evolution doesn’t stop. Evolution is, roughly, random genetic mutations, some of which provide characteristics that enhance the ability to reproduce, some of which impair it, and some of which have little effect one way or the other. The characteristic’s effect depends on the environment. If the environment changes, then the surviving characteristics tend to change. (This assumes the theory that acquired or cultivated characteristics are not passed along genetically, such as a giraffe getting a longer neck by stretching more to reach things and then its offspring getting a longer neck as a result.)

As other posts above mention, there are still plenty of people in the world that do not survive to reproduce. To extend the question, suppose that modern medicine and economics overcome that; then what course would human evolution take?

I appreciate that you put idea in quotes, but nonetheless you imply that evolution has a strategy. Evolution has no strategy, it does not ensure the survival of a species, it does not ensure anything. It is kind of a statistical process. It does have the tendency to enhance the survivability of a species, but that is not because evolution itself is some kind of goal-oriented process.

10

It is not quite what you have in mind, no doubt,
but whenever this question comes up I like to point out that the possibility of redesigning our own genome which may sooner or later become available thanks to advances in understanding in genetics
will allow the evolution of humanity to not only continue,
but increase, and humanity could exploit environments now closed to us.

SF worldbuilding at
http://www.orionsarm.com/main.html

11

Many types of mental retardation are either a result of mutation (Down’s Syndrome, Williams’s Syndrome, etc.) or a problem during pregnancy/birth that is more related to chance than genetics (i.e. being strangled by your umbilical cord). In the former case, you wouldn’t want to breed out whatever “tendency to mutate” genetic component might exist because that’s what’s got us to this high a level in the first place.

12

What about extinct species? Sure, evolution stops for them then, but that’s like saying life will be over when I die, I’d be only speaking for myself. Evolutionary phenomena (natural or manmade) led to their disappearance. When some other species may then move into the ecological niche, it will be subject to those same selection pressures. Evolution continues.

As per most accepted schools of evolutionary theory, the process is NOT teleological, it does NOT aim towards or require “evolutionary progress”. Once speciation happens, new species tend to stability until extinction whenever that happens, however that happens, it can be ten million years, it can be a hundred thousand; whether or not there are further speciation events within it, that leave any number of “descendant species”, is an entirely separate and not mandatory process.

H. Sapiens last speciated, what, 200K years ago? Agricultural civilization and fixed communities started less than 10K years ago, industrialized technological society as we understand it at most 150 years old and that’s for the lucky few. Hardly time enough to say evolution has been interrupted. (And BTW, with the human mind itself an evolutionary product, it’s not as if culture’s some sort of alien contaminant.)

13

No. It never stops. As long as their’s life as we know it, their’s evolution.

This reminded me of something I thought about some time ago. What are the average number of children per parent for law-abiding, civil, and forward thinking people? Does anyone else think it’s less than the average number of children for say the Death Row inmate population? Or the Prison system population period. I think it is (unfounded, just a hunch). It would be interesting to see these numbers. I’m sure they exist somewhere. If I’m right, this would lead me to conclude that being a “good” person, may not be the best human trait to have (evolutionarily speaking). Thoughts?

14

:smack: idiotic mistake on first post. Their’s to there’s. duh…

15

There are only two requirements for evolution:[ol][]individuals have different levels of reproductive success,[]those differences are at least partially hereditary.[/ol]Clearly, some people are more (or less) successful at raising children. I would be very surprised if genetics were not involved to some extent. Thus, the human species is still involving.

16

First, yes medical intervention is definately causing a shallower gene pool, at leat in modern societies, and deleterious genes are no longer selected against. This is a type of evolution however, even though it in general allows breeding of “weaker” indivduals. By definition, if the offspring survive, evolution has been served, even if the individual would have died before reproductive age 2000 years ago.

Inbreeding can cause both and increase and decrease in mutation rate. McKusick, the famous geneticist, based an entire textbook on the Amish, a highly inbred group. However, the Mennonites in Ohio and Indiana are even more inbred due to greater geographic isolation and serious hereditary disorders are almost unheard of. Darwin referred to this as genetic purging.

17

You practically answered your own question in those last two sentences, but failed to see it. Yes, those who previously might have perished as a result of “the environment” today might survive; however, that should indicate that it is the environment which has changed, not the workings of evolution. In an environment where medicine is plentiful, for example, there will be fewer truly detrimental mutations, so more individuals will survive to reproduce (how reproduction might be affected in such individuals is another, but important, matter). Remove those indiviudals from the medical environment, and they would likely perish.

Selection is merely a description of the interaction between the parameters for life in a given situation and an organism possessing the traits which are matched against those parameters. If the parameters change, the same organism which might have been selected against before may survive now. This is not a cessation of evolution, merely an alteration of its path.

[quote]
Originally posted by Pleonast
There are only two requirements for evolution:
[ol]
[li]individuals have different levels of reproductive success,[/li][li]those differences are at least partially hereditary.[/ol][/li][/quote]

Actually, there are three requirements:
[ol][li]Mutation[/li][li]Heredity[/li]Differential reproduction[/ol]

18

Short answer, yes, Western humans have stopped evolving. And yes, evolution can stop.

To further Pleonast’s post, and help clear up a few misunderstandings, Evolution by Natural Selection requires the following:[ul]
1.) The species has variation (some have blond hair some have black)
2.) The variation is a result of genetics (there are genes that code for hair colour).
3.) That variation is passed from one generation to the next (parents with black hair should have children with black hair)
4.) That variation provides an advantage (even slight) over the number of offspring (read grandchildren)à people with blond hair are sexually selected for.[/ul]

Point 4 is a bit tricky. If half a population of giraffe’s had short necks and the other half long, the long would be able to eat more than the short necks, and hence survive to produce more long necked giraffes (natural selection). Or, like with peacocks, the one sex selects traits like the length of the tail feathers or the size of the breasts… But try to keep in mind that its all based on having lots of grandchildren. It doesn’t matter if you yourself are very ‘fit,’ your grandchildren have to be at least as fit as you for the process to work. Humans have managed to sidestep most of this such that someone with black hair can die it blond, and someone who is short can use a ladder.

In Western society, I would wager that those selection criteria have ceased. It may seem that there are more women with larger breasts, but there is nothing stopping women with smaller breasts from having children (or getting larger breasts). In fact, there really is nothing stopping anyone from having lots of grandchildren. It would be nice to think that humans are evolving and becoming smarter but this too is wrong. Intelligence is only partially derived from genetics, and it seems to me that its now easier for dumber people to have lots of grandkids.

This is always an interesting debate, but evolution is one of those things that very few people can actually grasp. The real question should be: Within our population, are their any genetic-based variations that provide a competitive advantage?

Unless you can point to a specific trait, I’m willing to say Western humans have stopped evolving, at least for now. And yes, evolution can stop, when environmental pressures stop. Its quite possible that in 40 years we’ll have no ozone layer and people with darker skin will have a distinct advantage. UNLESS use fair skinned folk figure out a way to keep from burning…

{As an aside, sickle celled anaemia is probably the best example of human evolution.}

19

Evolution is still tearing along - Have a look at this…

:smiley:

20

Pleonast:

Um, that’s evolving.

dauerbach:

Actually, medical intervention is causing a deeper gene pool–i.e., increasing the genetic diversity of the population.

Darwin’s Finch:

Strictly speaking, evolution (specifically, a change in heritable traits) will occur even without mutation. But without mutation, heritable traits could (but not necessarily) become fixed.

emacknight:

Environmental pressures never stop. Evolution is not restricted to obvious outward physical changes. There is always an advantage to having an immune system distinct from majority around you. But for a definite answer, one could genetically sample the population every so often and compare gene frequencies.

Strictly speaking, evolution requires heritable traits, not necessarily genetic traits. I do not know of any heritable yet non-genetic traits in any biological species, but we cannot exclude the possibility. For example, perhaps the way a protein folds is copied from the parent’s folding pattern, rather than the DNA.