Ask the river—is it the same water that flows in it today as yesterday? Do the fish stay at the same shallows from season to season? Do the rocks on its bed remain unchanged in the decades and centuries? Does even its very path not meander and shift over millennia? Change is inevitable; the only questions are where do we start and how does the change take place.
Summary: we're evolving, and the ways in which we're evolving are changing. As time passes, social factors, and technological developments are likely to translate into genetic alterations, and have done so already many times.
These questions in this case pertain to evolution, and specifically to the evolution of humans. I doubt anything I say here will be especially original, except for some wild speculation, but it is of some interest nonetheless. The first thing to consider is how has the process of evolution itself changed, followed up soon after with some implications, and finally the promised sketchy speculation.
We can look at the evolution of humans as a fairly smooth transition, but even this transition has phases which I hope to delineate. The first phase is the longest and the most tedious—the phase of single-celled organisms. There is, however, one important thing to note here. For the first while, at least, they reproduced only asexually, which meant that evolution was fairly straight-forward. The organisms that were best adapted for pure survival prospered most. I shall call, somewhat inaccurately, this process in which selection is driven only by death "viability selection".
The next phase, encompassing the vast majority of interesting prehistory, is the phase in which viability selection coexisted with another selection process: sexual selection. With sexual reproduction, organisms learned that making a choice in your mate is a good idea, and with that choice came another means of selection. Now, while surviving was still key, getting a good mate, or often any mate, became crucial as well. While sexual selection, especially at the outset, still drove towards offspring with a greater probability of survival, this was something that happened in each individual pairing, but, interestingly, did not necessarily translate into maximising survivability on the whole. For example, a male with a beautiful tail is clearly able to take care of himself well enough to maintain this luxury, and is thus very fit. However, selecting for having a beautiful tail can reduce the survivability of offspring in the species as a whole. Thus, in the second phase, viability selection and sexual selection mixed together in complex ways, and both waxed and waned in importance sporadically.
The third phase then, is one that is unique to humans. If I had to choose a beginning for it, I would select the first agricultural revolution (c. 10000 BC), however its roots lie earlier, with the mastery of fire and the development of tools. Regardless, this stage is characterised by a greatly diminished role of viability selection. Many have unfortunately taken this decline to mean the end of human evolution, simply because the unfit hardly die any more. However, even setting aside that, with greater population densities, diseases became rampant as never before, the decline of viability selection more means a greater role for sexual selection than anything else. As this stage focuses narrowly on humans, there are some important single events that I believe had a qualitative effect on the process of evolution. As such I'll split it in two parts for this discussion.
From the beginning of the first part, even the strength of sexual selection became muddled. Because of the pair-bonding in humans, even if you are seen as an undesirable mate, you will still find someone (equally undesirable) who wants you. Seemingly, this ensures fairly uniform reproduction, but this is not quite so. Evolution here finds an outlet in adultery—even if you are with your mate for life, there is no particular reason you must bear his children, or inseminate only her, if you can get away with it, of course (I'm ignoring the ability to support additional children due to success for now). Indeed, research suggests that for most of history, people have gotten away with it, and that something like one in six men was responsible for more reproduction than the other five (my apologies for the lack of a source, I'll add it if I find it).
It is perhaps not surprising, then, that I consider the event causing the shift to the second part of this phase the invention and widespread adoption of birth control. With it in place, women can satisfy the evolved urge to seek the fittest mate, while men can satisfy the urge to mate with as many as possible, without risking as seriously endangering the long-term viability of the pairing (as would have happened if a male had to contribute to the upbringing of another's child). As such, I feel that the route of sexual selection through adultery has largely closed. In approximately the same period of time, however, another route has opened. With a less rigid social structure, women gained the ability to move from one mate to another, and eventually even to raise children on their own. This change to some extent broke the strict pair bonding system and has ensured that mating is less of a guarantee for each individual.
Thus, we have a move from pure viability selection, to a mixture of sexual selection and viability selection, to almost pure sexual selection, and perhaps to weakening evolutionary pressures even in that category. What's next? I don't know, although I have a few interesting guesses. Sadly, evolutionary biology is not, at present, an especially predictive science, so we'll have to wait and see if they're validated. Meanwhile, however, we can speculate to some amusement on the effects of the changes that have occurred thus far and those to come.
The first two phases are fairly boring and very long, so the assumption I'm going to make is that at entry into phase three, mankind was fairly stable and adapted to its environment. The rather recent disruption brought about by the phase three changes are then the matter of interest. Physiologically, it is a well established fact that we developed the ability to process gluten in response to the development of agriculture in general and bread-making specifically. This is not especially interesting, however, except to note that while receded, the influence of viability selection is by no means gone entirely, at least at this stage. However, with the diminished scarcity of food, the stops should have come off energy consumption, which would primarily benefit two things—muscles and brains, the primary energy consumers in the body. However, would these be selected for? I would argue for maybe, and yes respectively. With agriculture comes increased group size, with group size, increased social interaction, and with that, greater opportunities for advancement through intelligence. The case for muscles is more ambiguous, as demands for them fall, however selection for strength and intelligence both benefits from another factor. Since they require high energy inputs, we can expect that in phase two they would have been signals of fitness (as one who could maintain large muscles and brain must have ample food), and thus we can expect run-away sexual selection for these even in the later phase.
Beyond these simple effects, however, we should consider the outcome of the mechanism of sexual selection. In essence, males can choose one of two strategies: they may either be reliable and steady, thus enticing a desirable partner into a permanent pairing (by showing that they will be reliable providers for the offspring), or they can be promiscuous, thus showing they can produce offspring who will be successful at reproducing, in a self-fulfilling prophecy of sorts. A female's ideal strategy would be to respond by living with the steady type and having children with the promiscuous one, as far as possible while managing risk. The balance of the two male strategies will then be set by the ease of cheating, the level of its rewards, the probability of detection, and the level of consequences of detection. To be fair this balance is likely established more on the cultural level than the genetic one, but that also makes its shifts in response to changing circumstances more immediate and its outcomes no less interesting. The effects of these shifts should be considered before checking for their occurrence. We know, for example, with some degree of surety that, male homosexuality is commonly a result of someone's genes going for the stable profile, and then going a little too far. So, on that side we can expect greater non-violence, neatness, and perhaps some of the characteristics commonly associated with femininity. Juxtaposed against this, we have the high-masculinity option—I feel like I can't be sufficiently concrete with this, so I'll let your imaginations fill out the details.
I believe the overall trend can be viewed as flowing from greater consequences and risks in adultery at the beginning of this phase, to lower and lower towards the end of its first part. This is generally the pattern associated with movement from smaller traditional societies, to urbanisation, and mostly more liberal outlooks. If you live in a small community, or on an isolated homestead, and your husband begins to think ill of you, consequences will be much more dire than in a large city with greater opportunities. Thus, we can assume that evolution tended to shift humanity towards greater profligacy in this period, and people to give greater favour to intercourse outside of pairings.
At the entry into the second part of this phase, however, we can see birth control stripping away the majority of the evolutionary appeal of adultery. At the same time, however, greater independence for women tends to enhance the power of sexual selection. As such, two primary classes seem to emerge: independent females pairing with likely-to-reproduce males (and not infrequently caring for the child alone), and the more classical pairing of stable male with a female. I would argue that current trends point back towards stability becoming a greater favourite than before, and that to some extent this trend will continue until the next large shift in society. Of course all these strategic characteristics aside, I suspect that intelligence and, to a lesser extent, strength are still favoured either way, as are other runaway characteristics such as height (being tall is also fairly energy-inefficient).
So, all that weak conjecturing aside, the interesting question is where do we go from here? What will be the next paradigm shift? This is of course the realm of pure speculation, however I would suggest three likely paths. The most obvious is, as usual, that we're going to have more of the same. More independence for women, a looser-knit society, greater reproductive control. This is terribly tedious, however, so I'll let you work out the implications yourselves while I move on to the other two.
The second path for humanity is transhumanism. Frankly, I think travelling it is inevitable to one degree or another. We are driven to make ourselves as appealing to potential mates as possible, and enhanced strength, speed, intelligence, all have very high appeal. The two main questions with this path is how quickly will it come, and will it mean the end of evolution in the biological sense. Starting with the latter, the answer likely depends on certain factors. If we see something like the singularity, then probably yes, evolution will either stop or become irrelevant. If we only see enhancements, however, and especially do not see genetic modification or the indefinite expansion of lifespans, then it may continue. Even in this scenario, however, it is likely to be dwarfed in significance by technological advancements, and would be relegated to a secondary position. That said, insofar as the strong pressure of rapid change may exist, we may witness a further strengthened selection for intelligence and a downgrading in importance of physical characteristics, as they would be relatively easily manipulated. This also partially answers the first question—the slower the technological advance, the more time evolution has to maintain its relevance. However if this is the path that humanity treads, then we may see the true end of biological evolution at its end.
If you were less than enchanted with that last path, the final one is likely to further raise your hackles. If transhumanism is somehow avoided, or stalls, and thus evolution is given a lot of time, we may see something of speciation. The condition at the heart of this is the extent of upward mobility. The flow of reasoning is as follows. Pairings are created through encounters between individuals. Encounters will commonly occur in places of education (e.g. university or high school), at the workplace, or at social gatherings. Only the last of these avoids stratification by class, and even then those with a higher income may, for example, attend more expensive bars than those with lower. If we assume that these patterns lead to a reasonably high degree of pairings and mating within one's social class, the only intermixing of genes would come from movements of individuals between classes. I believe that the rate of individuals dropping from a higher class to a lower one is generally low, hence upward mobility is of the utmost importance. If it is sufficiently low that genetic mixing is infrequent, humans may literally evolve into two species. I would not presume to guess at their distinguishing characteristics, but the process would be extremely slow, taking at the very least millennia. Frankly, we're likely to kill ourselves off before seeing the effects of anything this interesting happening.
The path stretches out long behind us, and is shrouded in mist ahead. My one piece of advice is to watch our collective step, not least out of curiosity.
