Are there any scientifically based predictions or theories of future human evolution?

Question

Reading this question of the stack exchange got me thinking. I believe human evolution is an ongoing process and will not stop. Are there any predictions/theories about the phenotypes and genotypes of humans in the future? and how they may differ in a few thousand years compared to present day?

I remember watching a youtube video and in the video the user predicts that there will be two branches of human species; a short dwarf like species and a much taller species. I'm still skeptical about this claim. Is there any evidence to back it up?

One could argue that modern medicine is preventing natural selection. How will this effect human evolution?

Answer 1

Its pretty much impossible to predict what will happen in the evolution of species. Evolution is a parallel search with millions (or in the case of humans 8+ billion) of threads. Our adaptive capacities have never been fully understood and will always surprise us I think.

Of course that doesn't stop people from trying! The prediction you mention is based on one man's ideas of dominant selection pressures on humanity now... for a men's TV show. In Dr Curry's scenario, technology users, and economic disparity, producing Eloi and Morlock like dimorphism as in the HGWells book "Time Machine". This seems like hogwash to me. All socioeconomic classes try to find high quality partners and height and attractiveness will be hard to stamp out in a large segment of humanity.

Economic elites breed slowly and even if they will try to skim the evolutionary cream of humanity off the top, there will be plenty of beautiful, tall and smart people who will lack economic opportunity in my opinion.

There have been more serious, IMHO, questions about whether medical technology, which lets the sick recover and may even compensate for genetically problematic traits. There are no inoffensive examples I can think of so I'll take male pattern hair loss - apologies. If medicine allows all men (and women) to grow a thick shock of hair regardless of our genes then the baldness traits might spread through the species. Sure it could happen, but then most bald and balding people end up having children now anyway.

In fact since civilization has started feeding the hungry, making the hunting of wild beasts less important, causing the shrinkage of the male physique (we used to be much more muscular), inventing medicine and schools where smarts can be selected for, and giving us all more choice when it comes to mates, evolution has accelerated for human beings. The authors specifically cite social factors as being more important in our evolution now.

Answer 2

Predicting future evolution is always extremely difficult (or impossible), and this is especially true for long-lived organisms such as humans. Therefore, your question is basically impossible to answer objectively. However, the question made me wonder about what research there is on the topic, and if there are any hypotheses or attempts to measure current selective pressures. A quick litterature search yielded a couple of interesting papers that you might be interested to look more closely at (along with hidden "gems" like "Do Women Prefer More Complex Music around Ovulation?"). They all touch on aspects of ongoing evolution or selection in humans.

Reed & Aquaro. 2006. Mutation, selection and the future of human evolution

Finally, it is frequently speculated that both positive and negative selection acting in modern humans is slowing down or coming to a halt because of our increasing insulation from the demands of the environment by the use of technology. The lessons being learned from studies in humans and other species, in fact, suggest that we will continue to be under certain forms of strong selection well into the distant future.

and

In summary, the maintenance of our genomes against deleterious mutations could have been a major selective component in shaping levels of human genetic variation. In addition to the probable role of rank-order selection (Box 1), the purging of deleterious alleles in gametogenesis might be a particularly efficient way to achieve this.

and

Furthermore, although selection against mildly deleterious alleles might be relaxed in modern humans, selection for the fixation of new alleles could be intensifying (and these could be detected with genome-wide data and statistical approaches; cf. Ref. [45]). This suggests a shift from the maintenance of our genomes against new mutations towards accelerated genetic change for a subset of new mutations (and possibly an associated shift from genetic drift to genetic draft dynamics [55]) as a theme for the future of human evolution.

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Powell. 2012. The Future of Human Evolution

Abstract
There is a tendency in both scientific and humanistic disciplines to think of biological evolution in humans as significantly impeded if not completely overwhelmed by the robust cultural and technological capabilities of the species. The aim of this article is to make sense of and evaluate this claim. In Section 2, I flesh out the argument that humans are ‘insulated’ from ordinary evolutionary mechanisms in terms of our contemporary biological understandings of phenotypic plasticity, niche construction, and cultural transmission. In Section 3, I consider two obvious objections to the above argument based on the growing literatures related to gene-culture coevolution and recent positive selection on the human genome, as well as a pair of less common objections relating to the connection between plasticity, population size and evolvability. In Section 4, I argue that both the ‘human evolutionary stasis argument’ and its various detractor theories are premised on a fundamental conceptual flaw: they take evolutionary stasis for granted, since they fail to conceive of stabilizing selection as a type of evolution and drift as a universal tendency that dominates in the absence of selection. Without the continued operation of natural selection, the very properties that are purported to reduce the evolutionary response to selection in humans would themselves drift into non-functionality. I conclude that properly conceived, biological evolution is a permanent and ineradicable fixture of any species, including Homo sapiens.

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Keightley. 2012. Rates and Fitness Consequences of New Mutations in Humans

The human mutation rate per nucleotide site per generation (mu) can be estimated from data on mutation rates at loci causing Mendelian genetic disease, by comparing putatively neutrally evolving nucleotide sequences between humans and chimpanzees and by comparing the genome sequences of relatives.
...
A genome-wide deleterious mutation rate of 2.2 seems higher than humans could tolerate if natural selection is "hard," but could be tolerated if selection acts on relative fitness differences between individuals or if there is synergistic epistasis. I argue that in the foreseeable future, an accumulation of new deleterious mutations is unlikely to lead to a detectable decline in fitness of human populations.

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Nettle & Pollet. 2008. Natural Selection on Male Wealth in Humans

Abstract:
Although genomic studies suggest that natural selection in humans is ongoing, the strength of selection acting on particular characteristics in human populations has rarely been measured. Positive selection on male wealth appears to be a recurrent feature of human agrarian and pastoralist societies, and there is some evidence of it in industrial populations, too. Here we investigate the strength of selection on male wealth, first in contemporary Britain using data from the National Child Development Study and then across seven other varied human societies. The British data show positive selection on male income driven by increased childlessness among low‐income men but a negative association between personal income and reproductive success for women. Across cultures, selection gradients for male wealth are weakest in industrial countries and strongest in subsistence societies with extensive polygyny. Even the weakest selection gradients observed for male wealth in humans are as strong as or stronger than selection gradients reported from field studies of other species. Thus, selection on male wealth in contemporary humans appears to be ubiquitous and substantial in strength.

Answer 3

You can't predict the evolution of anything because evolution is driven solely by the environment. It is the environment that squeezes species into to specific forms. We have has a much say in our shape and form as a whirlpool does and for the same reasons, both humans and whirlpools result form powerful outside forces.

In order to have shot at even making a credible guess about future evolution, you'd have to know what the environment around humans will be over the next 100,000 years at a minimum. About all you can say is the likelihood of this or that modification, based on existing physiology. The more that has to change to evolve a new structure, the less likely it will, even given strong selection pressure. We won't evolve wings or eyes in the back of head but we could get taller, shorter, hairier, larger brained, etc.

The idea that evolution is the result of some innate guiding or shaping natural force arose shortly after Darwin advanced the theory of transmutation of the species by natural selection. The scientific community got on board with whole transmutation of one species into another, but they view natural selection as to happenstance and taking to long to be the primary mechanism. Instead they came to believe that some force was driving organisms to become more complex, in a particular pattern, over relatively short periods of time 1,000 of years.

That is why, we call the concept "evolution" in the first place. It was not a word Darwin used or liked because it had existed since the 16th century. Literally, it meant "to unroll" like a scroll and implied a preset motion or sequence. Seeds were said to "evolve" into plants. Sailors and soldiers practicing repetitive drills, practiced their "evolutions". The word meant the unfolding of predetermined pattern, the exact opposite of natural selection.

Unfortunately, this erroneous mechanism would dominate evolutionary theory for 80 years until the development of synthetic theory in 1947. But by then, the idea of evolution being predetermined, fixed, with "levels", "stages", "higher", "lower" and generally progress, had been fixed in the public mind.

So you still see a lot of nonsense about the "next stage of human evolution" when under natural selection such a concept is simple gibberish. We will be what ever the environment shapes us to be.

Answer 4

It is an interesting question, and I definitely agree with shigeta's question about medical technologies enabling the transmission of certain negative traits that would probably otherwise be less frequent.

Remember, evolution is really just a numbers game of whose genes get passed on the most. In general this was very strongly correlated with the fitness of that individual at being the best at getting food, attracting mates, and not getting dead. At this point we've got a fast food joint on every corner, and most people in the developed world live to be able to reproduce as many times as they see fit regardless of any reasonable form of fitness. Most people find a partner if they want one, and the incredibly fit do not procreate en masse like male leaders of packs of animals since polygamy is not an acceptable practice in many societies (notable human exceptions are cases like Genghis Khan who is thought to have fathered a ridiculous number of children [albeit this is not a great example of selection for a very nice trait]).

Just think about traits that people have who reproduce less, and traits people have who reproduce more, and we're evolving towards the latter. There is an absolutely hilarious (and depressing) intro to a movie based on taking these sorts of arguments to one extreme.. but I'm not sure this is the right venue to post it :)