There are thousands of species of spiders on Earth. Ditto insects. And, prehistorically, there have been times when there have been several, or even half a dozen species of hominins in existence on Earth at the same time. But, now, there appears to be only one species of genus Homo on Earth.
What circumstances could plausibly cause Homo sapiens to fracture into multiple species again?
A computer program eventually boils down to two different characters: 1 and 0. The only thing that matters is what order they appear in. But from that alone we get amazing tools, like for instance Stack Exchange.
A human is, at conception, apart from a little bit of cellular aid function, four different characters — A, C, G and T — repeated 3 billion times. Again: that which makes us humans and not for instance apes or fish or amoeba, is the order in which these characters appears.
The interesting part is that it does not take much reordering to make us from humans into something else. Humans have over 99% genetic commonality with for instance chimpanzees. That is a mere 30 000 000 base pairs that needs reordering, and voilà... a whole new species.
You have 99% genetic commonality with these fellows
So what happens when we can do genetic engineering on ourselves? Movies like Gattaca have already explored this venue. Human beings will start fixing the most glaring errors in our genetic code, like for instance the fact that our retina is clumsily mounted backwards, our idiotic vitamin C self-sufficiency deficiency, or our completely unnecessary vulnerability to viruses and bacteria.
So how long until we have the first "patch" to our genetic code? Will everyone get it? Can everyone afford it? Will everyone want to get it?
And what happens when another company provides a better patch, that it not at all compatible with the first one?
Even worse... what happens when we find out that husband and wife cannot conceive because they were altered by two different patches?
In real life, Pandora is looking at that big box that says "Human Genetic Engineering" and goes "Hmmmm.... I wonder what's in there"...
30 000 000. Otherwise your number is word-wrapped in my browser. Even if it didn't, it still has too wide gaps between digit groups with simple space.
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00,01,10,11.
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Commented
Oct 23, 2017 at 10:28
Planetary migration.
Think of how various races of humans developed on our world, people got cut off from one another for thousands of years, mutation and natural selection did the rest. Now imagine that instead of being isolated from each other by deserts mountains and oceans they're isolated by the vastness of space. Each one part of a completely different ecosystem. It's natural to suppose that in such an environment the human race would Branch off as various branches develop various mutations. Given enough time you would have entirely new human races develop on each planet. And if they have the technology to genetically alter themselves to fit better on the new planets then the changes can be even more extreme and happen faster.
Just be patient. We are right on the verge of elective genetic surgery as a medically available and culturally accepted option. In the next 20 to 50 years, procedures will become available which will modify your body's base code in a variety of ways. Few will be able to resist the allure of those new options.
Social and economic pressures when mixed with these new genetic opportunities, is a guaranteed recipe for the fracturing of our species into a multitude of new and reproductively exclusive species.
Dissatisfied with a single century of life, take this drug and live for five; but once you take it, you can't breed with short-lifers any more.
Having trouble in school? This simple process will double the blood supply to your brain and greatly enhance your intelligence and memory retention. But the genetic purist will consider you a gene-junkie forever more. Scratch off dating any of their daughters if you take that route.
What budding astronaut wouldn't take a treatment which greatly reduces their body's vulnerability to radiation, even if it meant that they could only breed with other astronauts from now on.
Just sit back and watch. The age of vanilla homo sapiens is just about over. In the days to come, we may all still be human, but most of us will be human+...
Again? Many hominins may have been able to reproduce with each other, making them, at least, subspecies. Generally while there had been a diversity of hominins Homo sapiens have been the one species overall. This remains an open question. The theories and evidence are contested.
As modern humans spread out from Africa, they encountered other hominins such as Homo neanderthalensis and the so-called Denisovans, who may have evolved from populations of Homo erectus that had left Africa around 2 million years ago. The nature of interaction between early humans and these sister species has been a long-standing source of controversy, the question being whether humans replaced these earlier species or whether they were in fact similar enough to interbreed, in which case these earlier populations may have contributed genetic material to modern humans.
Spiders evolved 380 million years ago, humans between six to three. Spiders have been able to differentiate into multiple species by exploiting different ecological niches. Humans haven't had enough time or occupied habitats sufficiently different to evolve into new species. Reproductive isolation, adaptive pressures & an enormous amount of time are needed.
Open one-way portals to parallel Earths and you're in business. Isolated populations of humans on alternative versions of planet Earth. Vast tracts of real estate to occupy. New environments to inhabit. The whole business of hominization can go down a new road.
Typically, species tend to form when populations are isolated from breeding with each other. Unless the world becomes significantly less globalized, and remains so for millions of years, it is unlikely for humans to speciate through that route.
Pure gene therapy is unlikely to be enough. Today, most people see particular qualities as being "good" or "bad", and most genetic engineering would be focused on making people "better". This would likely result in decreased diversity among the human species, rather than the fragmentation you're looking for.
However, a societal reform, a change to the way we think of "individuals", along with gene therapy, could provide another route.
Imagine a world where every person is born into a particular job, where their entire worth is determined by how well they perform at that task. Families grow more suited for their task, and tend to produce children with others who have the same societal role. This could, theoretically, result in fragmentation, where each "breed" of human is built to their task - much like dog breeds have been historically. You could have bulky construction workers, autistic super-genius engineers, subterranean tunnel-workers with good night vision, hairless and adaptable space explorers, even cute and docile "human pets". Breeding humans who excel at and enjoy their assigned task may prove to be easier and more efficient than creating robots for the same purpose.
While it is unlikely that such a society could last long enough for true speciation to occur (even dogs, which have been bred for thousands of years, and have tremendous diversity in form, are still the same species), genetic engineering could accelerate the process. Given enough time, human society could wind up as an ecosystem, with each human species providing something of value to the whole.
I'll start by quoting Darwin:
A second great fact which strikes us in our general review is, that barriers of any kind, or obstacles to free migration, are related in a close and important manner to the differences between the productions of various regions.
—On the Origin of Species, Chap. XI
You need barriers that limit to the minimum the breeding of two (or more) populations for enough time to allow mutations to arise that make it almost impossible to interbreed.
For current human conditions (low evolutionary pressure), it would take a lot of time… but on other conditions, it could be less time. Some factors that can explain an abrupt divergence:
Founder effect: "the loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population".
Convergent evolution: "the independent evolution of similar features in species of different lineages". It may happen that two populations or even species found homologous structures but with different coding.
Ecological niche: "the fit of a species living under specific environmental conditions".
Evolutionary pressure: " a quantitative description of the amount of change occurring in processes investigated by evolutionary biology".
With that, you can imagine, as an example, a cataclysm that isolates a small populations (then we have founder effect, but enough big to have a minimum diversity). The cataclysm (or the isolation circumstances) put a high evolutionary pressure, that prioritizes some characteristics that makes better adaptation to some ecological niche.
Even if the other (or others) population has similar circumstances, the chance favors different evolutionary ways, giving convergence at the most. But also there are chances that evolution produces two different approaches to the same problem.
I'll add some examples:
Humans don't reach sexual maturity until after puberty, which means that there is at least ~15 years between generations. This means it can take a very long time for any trait to develop.
There is some evidence that puberty is occurring earlier. If the trend continues or accelerates, that could make evolutionary changes that would lead to speciation quicker.
Genetic engineering would also fall under this category, as large genetic changes could be implemented and tested for viability quickly.
Either an increase in the rate of genetic mutations or a decrease in the ability to prevent mutations could increase the mutation rate.
For example, some condition (e.g., a disease/virus) that decreased human DNA repair enzymes could reduce mutation prevention and lead to a greater mutation rate.
Similarly, some event that increases global radiation could increase the frequency and severity of genetic mutations. (nuclear weapon, damaged atmosphere, change to sun resulting in more UV, etc.)
The same process that humans have used to selectively breed plants and animals to emphasize certain traits could be applied to people. This could either by encouraging/ forcing certain people to mate or by preventing them from doing do. See eugenics.
Some sort of physical or virtual separation of groups would be necessary. Physical separation would likely have to involve some restriction in travel via air or water - perhaps a nuclear war, severe climate change (e.g. ice age), or massive tectonic event.
Social/regional segregation. Split a group of humans into two separate groups. Let's say one lives in a rural area in the arctic, the other on a big plain around the equator where there can be 100s of meters, maybe even kilometers between houses. The first group will eventually evolve to get better eyes, and eyes on the sides of their faces because those with better eyes can spot polar bears more easily and have less chance to be eaten. In the second group, more athletic people can travel more easily and more quickly between houses as a child, which makes them get easier social contact, so they become more successful and have a higher chance of reproducing. After a long enough time group 1 will become hyperaware humans with very good senses and see high with contrast, and the other will be very strong, athletic people who can run very fast.
For the second scenario, let's get 1 country full of normal people. Now, a group of tall people thinks they are superior. All the politicians are tall, and they make a law so anyone above 1,85 is considered tall, and anyone below 1,85 short. Tall people get more rights, short people less. Now if a tall person marries a short person they get the same rights as that short person. All the tall people will only marry tall people, and short will marry short people. After a while, you get very tall people, and the rule is changed. Anyone below 1,90 is short. After a while, anyone below 2m is short. Now anyone between 1,90 and 2m isn't allowed to get children. After a few thousand years, human race is split between superior giants and small weak dwarfs.
