I have a question about evolution, specifically, when an organism (plant or animal) reaches a state in which it is perfectly adapted to its environment, does evolution stop? I ask this, because it seems we have several species which have stopped evolving. Take the ginko tree-I’m told that the modern ginko tree is essentially unchanged from the ginkos of 100 million years ago. So what does this mean? That the tree is so well adapted that no change to it is necessay? Or is the ginko species a dead end (evolution wise), and in danger of dying out? Seems to me that any species that lasts this long should have quite a number of advantages-so is the ginko an example of superb adaptation, or an eveolutionary anachronism, in danger of extinction? 
Evolution will continue as long as the plant/animal continues to reproduce successfully. For example, what happens if the earth starts to heat up? The Ginko tree may be able to handle the change or not. It may have to adapt itself to the changing environment so that means that evolution via natural selection will once again begin. No living plant or animal is immune from continued adaptation to change…
No. Environments, no matter how stable they may seem, are always in flux. Add a few more individuals, and the competition for resources heats up ever so slightly because now there are that many more looking for dinner and mates, for example. You’ve got more waste in the environment. You’ve got less territory available, and so on. Evolution may slow a bit (as it tends to do in large populations; the larger the population, the longer it takes for any “new” traits to become fixed in that population), but it never stops.
It means you’ve been misinformed. The ginko tree that survives today is not the same tree that was around 100 million years ago. Sure, it’s closely related and morphologically very similar, but species don’t last 100 million years. There’s a difference between “essentially” and “absolutely”. Basically, ginkos are morpholoigcally conservative over the past 100 million years at least, but that doesn’t mean they’ve ceased evolving.
Richard Dawkins had a lot of interesting thoughts on this subject. If you are the slightest bit interested in evolution, I suggest you pick up a copy of “The Selfish Gene” as well as some of his later books. It’s a very engaging read.
You might be thinking that if an organism reproduces over very long periods of time without change, evolution has “stopped”. Not really. Although it is obvious that that particular organism is well adapted to conditions, perhaps a wide range of them, it is entirely possible that a random mutation spins off another species that is also well-adapted, perhaps more so for particular conditions. It’s even possible that the two species do not compete due to different ecological niches or geographical separation, so the spinoff might not put negative evolutionary pressure on the parent species.
The only reason I can see for evolution to “stop” is if random mutations cease or selection by survival no longer works.
Are humans really still evolving? I mean with our medical technology is it really survival of the fittest? People are being kept alive who would normally die, as well as people who should have died a long time ago.
All life evolves. We have created a more stable environment for ourselves, but there are still diseases we can’t cure and there are still random mutations being introduced in every new generation. And remember-- most of the people in the world do not have access to 1st world medical technology. So even if 1st world medical technology stopped evolution (which it doesn’t), that would only apply to people living in the 1st world.
Keep in mind that evolution doesn’t necessarily mean speciation. Humans are unlikely to split into different species unless we travel to other planets and then become isolated for a long period of time (hundreds of thousands of years), or there is some cataclysmic event that reduces us to isolated bands of hunter/gathers. There are no truly isolated populations of humans on the earth anymore, so we are one gigantic breeding population.
We may, as an entire species, evolve into some newer species at some future time, but that’s a tricky thing-- saying two population separated in time (not space) are different species. There is really no way to test that hypothesis, so you just go with a morphological argument for saying the two groups are different species. This is what we do with fossils we find. Is this 500k year old fossil a different species from us? If it looks different enough, then we say it is, even if we suspect it to be in our direct line of descent. But biologists argue about this all the time, depending on whether they fall in the lumper or splinter camp on any particular decision.
I started another thread on this issue. My opinion is that human evolution is probably going faster than ever.
Just wait until genetic engineering comes of age-- we’ll be “evolving” like nobody’s business then!
Ah ha! I’ve caught you being imprecise (but never wrong)!
The overarching process of evolution–that is, the sum of mutation, genetic shift, recombination of available genes, et cetea–is almost essentially constant in any stable population. Some environmental effects–ionizing radiation, mutagenic solvents, genetic exchange from viral contact (especially retroviruses)–can affect overall rates of mutation, but the rate of viable mutation is essentially constant for any given part of an established and functional genome. And given a relatively static environment and selective impetus, the same combination of characteristics and capabilities will be repeatedly selected for, which is why the shark today is very much like sharks 100 millino years ago. It’s not that they’re not adapting and therefore evolving, but they’re adapting to essentially the same pressures, and thus the adaptive solutions are similar, fitting into a so-called evolutionary niche (though it’s important to note that such a niche is a post-facto observation, not a teleologically created category).
So species evolve, and that rate is mostly constant, even if they’re staying put in a functional sense. Only when environmental or other adaptive pressures change dramatically do you see large shifts in form and capability. (Which I think is what Darwin’s Finch was really trying to convey.)
“Survival of the fittest” is a terrible misnomer that gives rise to numerous misperceptions about how and why species evolve. “The fittest” may fit itself right into a dead-end niche, like the large predators of North America. “Survival of the most adaptive-ist” might be a better statement, but even then it implies that flexibility is the key to reproductive success and species survival. In reality, “the fittest” is largely luck in being in the right place at the right time with the right tools to succeed, and many very successful genus and classes have utterly disappeared for reasons we can only hypothesize.
As for people, our medical technology has only been around in anything like modern form for about a century. Before that, we were certainly subject to any disease or illness that came along without much more control than one’s own natural defenses, hence why the natives of the Americas fell to European conquistadors and pilgrims without much of a fight; the Europeans, adapted to (or perhaps more co-adapted with) infectious organisms like smallpox could survive and even carry infestations that wiped out whole swaths of natives. Even modern technology only takes us so far, and some people clearly have reproductive advantages over others. One might view the application of modern technology as merely an extension over our evolution; artificial selection for those with access to technology that increases reproductive likelyhood. No species is static.
And for a dissertation on why men are doomed to obsolecence I recommend Campbell Scott’s disturbingly amusing monologue in the opening scene of Roger Dodger:*Our ability–men’s ability to read maps, to navigate, makes us useful. You should discourage your sister from even looking at a map…Every cell in the human body contains a copy of the genome pattern. The only reason sperm cells have all the fun is that up until now, they were the only ones with access. Within Christopher’s lifetime, artifiicial insemination will render sperm as useless as an assembly line worker in Detroit…Think of the structure of the female genitalia. What is the most sensitive part of the vagina?..It’s the clitoris, first discovered by Renaldus Columbus in 1559…The crown of the clitoris contains 8,000 nerve fibers. It’s a far great concentration than in any part of the male body, even our fiingertips. It is the most efficient, pleasure-delivery system ever devised by nature.
Now, ask yourself, why didn’t the clitoris end up inside the vagina, so that intercourse would be naturally compellingly, constantly pleasurable for a woman? Because in primitive time, women died of childbirth. So for intercourse to be too pleasurable wouldn’t make sense from a Darwinian standpoint. What does that tell us? That for women, intercourse and sexual fulfillment were never intended to intersect. New technology just makes it official. Future generations of women will evolve clitorises…that are larger, longer, even more sensitive. And a woman’s ability, as well as her desire to self-stimulate will increase exponentially as intercourse is robbed of its procreative utility. The species is not static. We’re in a constant state of flux. Two genders has been the default setting for one reason only: So far it’s been the only way to propagate the race.
So where are we headed? Equality? Equality, what is that? Is that a principle of nature? We all sit around reading subway maps together. No. Of course not. Natural selection. Now that is a principle of nature. Selection. Something has to lose. Something has to be defeated in order for something else to be selected. It means that ten or fifteen generations from now, men will be reduced to servitude. Technology and evolution will have combined to exclude sperm from procreation and our fiinal destiny will be to lift couches and wait for that day when telepathy overcomes gravity, and our gender’s last remaining utility is lost forever. Forever.*The science is a little suspect, but the overall theme is correct…and frightening. (And creepily ironic in the context of the rest of the film.)
Personally, I’m discourging every woman I meet from learning how to read a map.
Sgtranger
I think you have an important point. Up until recently, evolution was blind to results. Then man started “playing god” and reproducing or allowing to reproduce organisms that would not have survived without this artificial help.
I think that the amount of this artificial help is too little to have any significant effect on evolution up to now. But ask this same question a thousand or a million years from now, and you might get a different answer.
If we still exist.
Well duh. Everybody knows that you lift couches with telekinesis.
I believe current thinking is that reproduction of the fittest is a more accurate term, after all, in the end, the fittest die as surely as the unfit. Sure, you have to survive long enough to breed, but ask a peacock whether evolution favors a long life over being hot to the peahens.
Stranger On A Train
That is, in essence, what Charles Darwin meant when he said:
“It is not the strongest of the species that survives… nor the most intelligent that survives. It is the one that is the most adaptable to change.”
Of course, since this is the SDMB, I suppose about 99% of you have already heard that.
Ah ha! Yes, I was being imprecise (limited by time and all that). Mutation rates do not directly affect the pacing of evolution, they merely alter the pool available for selection to act upon. I was referring to the overall change in allele frequencies over time (which is itself an imprecise measure of evolutionary change, but it’s one you gene-centric types seem to like 
). In large populations, for example, it may take several more generations for a particular allele to become “fixed” than in a smaller one. Thus, the overall rate of evolutionary change can be damped by large population sizes.
Further, evolution can be constrained by developmental canalization, whereby developmental pathways are fixed to such a degree that even minor changes render an individual unviable. This tends to limit the number of “new” mutations which can have a significant phenotypic effect, thus contributing to a conservative morphology. And, of course, there’s the concept of mosaic evolution, whereby different traits evolve at different rates. Further, there’re also the concepts of phylolgenetic rates (wherein characters evolve within a lineage) and taxonomic rates (whereby taxa replace one another over time). So, yeah, imprecise, but a good example of a case in which the overall rate of evolutionary change can be slowed.
Regardles of the pacing of evolutionary change, though, evolutionary mechanisms are acting always.
Not really, but it’s a good example, too. The greater the selective pressure, the greater the degree of change within a population. Of course, high selective pressures are usually brought about by catastrophic, or nearly-so, changes in the environment (which is not to say that new traits will arise more quickly or anything like that; rather, a catastrophic change can drastically alter the gene pool of a population by killing many members; this can result in a different “trend” for that population down the road, coupled with a smaller population size, etc.), while gradual changes result in gradual shifts in selective pressures and a slower rate of overall change.
That depends. As I alluded to above, taxonomic rates can vary from lineage to lineage, and may even vary within a given lineage. For a given population, it depends on whether you are looking at individual characters or allele frequencies or the trends of the population as a whole, etc.
At some point in the relatively recent past, some populations in Africa and the Mediterranean developed a variation that gave them some resistance to malaria. Unfortunately, carrying two genes for that trait causes sickle cell anemia.
At another point in the relatively recent past, some populations in Europe developed the ability to tolerate lactose well into adulthood, enabling them to gain nutrition from dairy products.
It has been suggested that the descendents of survivors of the bubonic plague a few centuries ago have passed along genes that also make them more resistant to other diseases, possibly even HIV.
Evolution never stops. But it takes quite a long time for even beneficial changes to become widespread.
Well, you personally stop evolving when you are conceived. Then you either die without progeny, or your progeny evolve. But not a whole lot.
Tris
Excatly the opposite is true: humans live in the most variable and rapidly changing environment of any vertrebrate species on Earth, probaly the most rapidly changing of any spec ies on Earth. What other species has to cope with a complete and total change its physical environment every generation? Most humans just 50 years, ie within the current generation, ago made a living as farmers. Now very few do. Most humans 50 years ago didn’t need to deal with powered machinery at all. Now every single human on the planet needs to deal with that. most humans had aver limited range of food products regularly availabel, now every huamn is exposed to countless different food products and the pesticides and preservatives associated with those products. Most humans woudl use less than 10 drugs in their entire lifesapn, now most people are exposed to 10 within the first year of life. The same with novel diseases, novel risks such as exposure to various food additives and so forth.
In contrast to the dynamic environment that humans have created for themselves most organisms exist in an environment that changes at a literally glacial pace. New foods and chemicals become avaialble only as a result of evolution and climatic shifts, new disease evolve rarely, the means of obtaining food and the general structure fo the environrmnt similarly changes only with climatic shifts.
For the life of me I can not undersatnd why so many peope think that the human environment is stable when it is so demonstrably false. Nothing that I do and almost none of the major risks that I face are the same as for my grandfather when he was my age and that is true for the majority of people on this planet. Yet somehow our enbvironemntis thought to be stable. In contrast every risk that a chimp faces and every thing that he does is exactly the same as for his forebears 100 generations ago.
If the environment of a species remains perfectly stable, then yes, it’s likely that the species will not undergo much evolution do to external selection pressures (“natural selection”).
But it’s possible to have non-environmental selection pressures such as changes to the organism that make certain members more likely to reproduce than other members, such as things like plumage that attracts attracts mates. Then, even though those members aren’t more fit than their environment, they they are more fit to find mates, or more fit to produce more offspring.
And even in the absence of all selection pressures, there is the simple fact of “random drift” - random changes to any system will tend to lead it in some random direction despite the fact that individual changes on average aren’t in any particular “direction”.
You can see this with coin tossing - even though the chance of heads or tails is the same every single time, the average of heads or tails is not going to remain exactly even over a long time.