On other forums I have asked this and most seem pretty sure that we are still evolving and that given a sufficient amount of time we might have descendants who could no longer interbreed with ourselves.
What I don’t understand is how reproduction success would factor in to the equation. Given the emergence of a particularly virulent influenza which avoids inclusion in yearly flu vaccines, there could perhaps be a massive editing of our genome down to the lucky individuals with natural immunity. But short of such a catastrophe, I don’t see how traits that infer greater fitness can be selected for when the question of who breeds and how much is determined by so many other factors beyond the bare opportunity.
I’m not sure if this is anything serious science wonders about.
I think you are asking about whether there is good evidence of differential reproductive success in current human populations. There is. One example below.
Given a present lack of reproductive isolation for any major groups, would it be accurate to think that any “drifting” we are doing, we are doing as a more-or-less monolithic world-wide unit? I.e. – for at least this tiny blip of geologic history, our evolution would be a linear, if meandering change.
Thanks for trying, Stephen, but I’m afraid that pretty much went over my head. Is there a dumbed down way to say what mechanism the authors of that paper think they’ve found for differential reproductive success?
There are a lot of interesting topics in the opening post.
First, the question of interbreeding. As of right now, we don’t even know if there would have been fertility problems between us and our ancestors from 200,000 years ago. Apparently, we were even able to breed with neanderthals to a limited extent, and our populations had remained separate for hundreds of thousands of years prior to that point, so perhaps there wouldn’t have been a problem. The horse and donkey lineages split about 2 million years ago and they are no longer able to produce fertile offspring due in part to a chromosomal fusion that happened in the horse lineage. I don’t think there is any hard and fast rule on the timing of the loss of fertility, but I would say that it is probably inevitable at some point. I would also say that natural selection may not play a role in the loss of fertility. Neutral drift could also fix alleles that prove troublesome for fertility.
The other question is if the human population is still affected by natural selection, and that answer is definitely yes. @glipsnort may be able to cite papers dealing with signals of positive selection in the human genome. The one example that I find compelling is the selection of hemoglobin alleles due to endemic malaria. The most infamous allele is the sickle cell trait which confers malaria resistance, but if you carry two copies it causes negative effects. Therefore, there are both positive and negative selection pressures on these alleles, and that is exactly what we see when we map the prevalence of the sickle trait and compare it to a map of regions with endemic malaria:
There is also a rare allele, HbC, found in population pockets that confers resistance to malaria, and some studies have suggested that the HbC allele may replace the more common HbS (sickle cell) allele in future generations:
“Overall, it generally appears that allele C will quickly replace the S allele in malarial environments. Explicit population genetic predictions suggest that this replacement may occur within the next 50 generations in Burkina Faso.” Hedrick (2003)
Sexual selection: people choosing mates based on perceived good qualities.
On the topic of natural selection, it is interesting to note that some characteristics that helped our ancestors survive may in fact be detrimental in our modern society: things like our instincts to prefer food with high calorie counts (lots of fats and sugars) and to do so while expending the least energy possible, using our brains to figure out ever more clever ways of increasing sugar accessibility. Good for surviving on the savanna; not so much for office life!
It gets to be a mess with human reproduction. I think we can consider ourselves one relatively homogenous population, so any factors would have to be global. Warming perhaps? Also with increased population density, perhaps dietary requirements. One thing is sure, we are unlikely to develop bigger heads and bigger brains like the science fiction comics show. At least that is my opinion, as people seem to not be getting any smarter, and smarter people seem not to thrive.
Well sure that’s entirely possible. It’s been true for virtually everything else but its kind of a moot point as yes perhaps (if humans lets say continue for 2 million years) humans two million years from now could not interbreed with humans today nor would they probably want to - as it seems the future for our species is actually probably one of genetic modification, i.e. literally ‘intelligent design.’
Some random ways our genome has changed in the past several hundred years:
On a smaller scale, ~10% of Europeans are virtually immune to HIV thanks to the black death. Could something like this happen again? Possibly as we are more connected than ever as a population.
Here is a model that describes the increase of fetopelvic disproportion (FPD, i.e., the fetus is too large to pass the maternal birth canal) due to our ability to perform Cesarean sections.
With several beneficial mutations that we find around the world in smaller pockets, it is quite likely that we will someday aim to assist their spread into the population as a whole- things that are generally good for everybody (longer life, resistance to heart problems/various diseases, etc.).
Pevaquark edit- to provide the perspective of Berkley’s evolution website as well:
Those are interesting sociological observations that we can note and act on today. As regards evolution, though, our brief span of observation (even as a ‘civilization’ much less within the context of a single human life!) is such a tiny blip that I can’t see how these observations can rise above mere speculation as to how they would look (if indeed they show up at all) within the enormously “panned-out” view of geological time. There would be so much else going on … climate changes, other diseases or pestilences – myriads of other things in play, not to mention the occasional meteor impact or major volcano, that any little differentiating factor we take an interest in would be competing with an immense amount of noise. --Noise which is still present even while focused into our tiny “blip” here. So while the mechanisms discussed all seem plausible enough in their own right, I suggest the task [of plugging them into larger human evolution going forward] would be more analogous to speculating on global climate change while only having access to a couple thermometer readings in a single day at Winthrop, North Carolina.
Looking back, is of course, an entirely different story. As it seems some of these mechanisms can be seen to have risen above other noise in retrospect.
Looking back what we find is obstacles shaping who would successfully be able to rear children, but it certainly looks as though there has been a pretty uniform drive to produce children where possible.
Looking forward I’m not sure that drive will or should continue. Since we are conscious of the earth’s limitations to sustain us beyond certain physical limits, it seems fitting to choose to reproduce less. Our ultimate survival may even depend on it. So it seems the linkage of fitness to and actually choosing to reproduce is broken, and needs to be.
And doing so will effectively represent a divergence from the usual mechanism of fitness leading directly to greater reproduction. Now we engineer the world to suit our fitness so I don’t see how individual variation will much matter.
That’s probably roughly accurate, except that selection has been altered significantly by (for example) medicine. So, in some human populations, previously lethal mutations (or variants that would otherwise have led to near-zero reproductive fitness) are preserved. This creates opportunities for hitchhiking, for example, which is one example of how evolutionary change can continue and even be redirected. Since human subpopulations differ significantly in the influence of medicine, we might expect differences in rates of drift/selection/evolution despite lack of reproductive isolation. Consider last paragraph of this paper by Michael Lynch:
I am assuming that “still evolving” in this thread title refers to observable changes in the Homo sapiens phenotype; i.e. changes brought about by “survival of the fittest” as determined by the possession of the most favorable alleles for the environmental conditions currently present. As @Mervin_Bitikofer points out, human domination of the planet plus the ease of transportation prevents reproductive isolation to the extent that biological evolution is likely to be much slower now than it was in the past.
Using the nomenclature initiated by Teilhard, a new sphere appeared on earth some 50,000 yrs ago–the Noosphere, the sphere of Ideas. Through the recently invented language, these ideas followed the ‘law’ of survival of the fittest. (Dawkins dubbed these “memes”, but I prefer ‘Noogenes’ to acknowledge Teilhard’s priority). Currently this phenomenon is most often referred to as Cultural Evolution. IMO, the future of Homo sapiens is going to depend much more on Noo-evolution than upon Bio-evolution. Perhaps those working on the bioethics of using CRISPR-Cas9 in human gametes will determine the direction this new Intelligent Design should take.
Al Leo
That’s too narrow, too many codicils, IMO. Too much emphasis on “survival of the fittest,” which is unnecessary for evolution, and on “environmental conditions,” also unnecessary. Sexual selection is a strong driver of evolution, for example. But anyway. Sorry to carp.
It could also be that we try to blow ourselves to smithereens and reduce the human population down to a few thousand people in a nuclear winter . . . but I like your idea better.
A nuclear winter with population loss and opened ecological niches would certainly be similar to how many species came about, but hopefully we can avoid that scenario.
There is no doubt that dozens of responders in this forum are better educated than I in the areas of genetics and evolution, but if the ability to adjust to changing environmental conditions has NO influence on evolution, then I should remain silent on these topics. I have no idea how I became so misinformed.
Al Leo
In biology, this is called niche construction. The idea goes all the way back to Darwin himself. In fact, Darwin’s last published work was about earthworms:
In the book he describes how earthworms change the soil around them, creating niches for plants, molds, and other animals, as well as creating an environment that produces food for the earthworms themselves. Darwin even constructed indoor habitats so he could study earthworms up close and personal. He was a bit obsessed with them, one might say.
Today, some scientists are claiming that niche construction is this brand new and revolutionary idea that requires a rewrite for the theory of evolution. I guess they forgot to read Darwin’s own work.
Is there a dumbed down way to say what mechanism the authors of that paper think they’ve found for differential reproductive success?
