Self inflicted extinction in a modern setting - Plausibility and Duration?

Question

Suppose there exists a species of humans which are better physically, mentally and aesthetically(in a conventional way) by at least three standard deviations(any large margin will do) when compared to Homo sapiens.

And when that species sexually reproduces with a Homo sapiens partner, their offspring will only inherit DNA of that species. I'm thinking for males their sperm will contain viruses which eliminates unpaired chromosomes in the egg of the female partner. For females the sperm from their partner is ignored once it reaches the their egg, and its just a sign for the egg to begin duplicating. However the offspring will not look like a direct clone of the non Homo sapiens parent. The species has a bank of DNA in their sperm or egg cells that determines the facial structure. Before reproduction, their brain will have already created an image of their partner and released certain chemicals which turn on or off certain genes in their reproductive cell such that the their sperm or egg will make the offspring look similar to both parents. The offspring retains the same ability.

They have no language or culture and will integrate into any community they are brought up in. Suppose there are 2000 of them to begin with, they are scattered around the world and have attracted no attention to themselves.

How long would it take for Homo sapiens to breed themselves into extinction?

Would there be any real opposition if they really are better in every way and integrate well into whatever environment them find themselves in?

Would extinction be achieved even sooner if the offspring looks aesthetically similar to the race it breeds with? Or would it be quicker if the offspring is more conventionally attractive?

What I cam trying to ask is how quickly will natural selection by the environment and potential partners have an effect in a modern setting.

Please also suggest on any other plausible genetic traits you think would increase their sexual competitiveness.

Answer 1

You are over complicating a real world phenomenon

If they don't inherit genes, then the offspring will be rejected during pregnancy as a foreign organism no matter how much it look like a human. For example, a hyena can not breed with a dog no matter how much convergent evolution happens. But, if you flip the problem and say that they have enough common genes as humans to successfully reproduce, then no one is really going extinct because what is really happening is just the proliferation of a genetic trait. Man kind does not go extinct, we just evolve.

Genetics already has a common mechanism that will achieve more or less what you are asking for which is the "dominant trait". A dominant trait is a genetic characteristic that will replace its paired trait when both genes exist in the same organism. For example, if you have the genes for both blue and brown eyes, you will inherit brown eyes. Not bluish brown, but brown brown. This is because the gene for brown eyes is dominant to the gene for blue eyes. Likewise, let's say that humans evolve a mutation for super intelligence, and that this gene is dominant to not super intelligence, this means that everyone who inherits the gene will be super intelligent even if they also carry the stupidity gene.

Maintaining old recessive genes instead of destroying them makes a species far more resilient than getting rid of them entirely because it is very common for a gene to be superior in some contexts, and worse in others.

Your scenario could not happen naturally because it would require a ton of separate mutations, but perhaps a scientist could mess with human genetics to make a bunch of superior genes that are dominant to all genes they could replace and would spread into the rest of the population. So your "parent zero" generation would all have not 1, but many new dominant mutations.

How this would work in normal genetics is that thier children would all express the gene even if they mated with unmodified humans. Then if the hybrids mated with more unmodified humans, only some children would carry the gene; so, not all grandchildren of the super humans would have the gene at all, but some would, and they would continue to pass and spread the gene.

If your gene destroys the human gene and always inserts a double version of the gene instead of a dominate gene, you will reduce your genetic diversity which can lead to all sorts of problems.

To answer your question, natural humans may still be more selectively fit

There is no such thing as universal fitness. In the process of natural selection, it is not always better to be faster or stronger or smarter. An animal's selective fitness is all about filling whatever niche's are available, and niches can disappear.

If a new disease emerges that targets your super humans, then you could quickly go from 90% natural human replacement to only natural humans being left, but if you mix the genes normally, then maybe everyone with the super speed gene gets wiped out, but your super strength and intelligence can remain because they are not forced paired.

Another way your super human experiment might fail is that they are too well adapted to modern life. They are so good that they rapidly reproduce and overconsume resources. What you may see happen is that your new super humans progress very quickly into a period of behavioral sink or an Easter Island scenarios where your super humans outgrow thier environment faster than natural humans leading to more wars, more famines, more cannibalism, more sexual abstinence and/or homosexuality, and thier eventual extinction. Most social organisms experience behavior changes as thier group grow in size to prevent overpopulation, and if your super humans are anything like mouse experiments that have been done on this topic, they will not just self regulate into equilibrium, they will self regulate into extinction.

So, there are actually a few possible scenarios that the few remaining pockets of slow, weak, dumb humans will be the only ones left after a few centuries, and not the other way around, but if you add new genes that blend into the human race, then we will use those traits to evolve in whatever direction we need to evolve in with each subsequent generation without having to fully give up on any given option.

Answer 2

Brood parasites do take a huge toll on populations.

There have been some recent news reports, notably featuring Pope Francis, criticizing a trend of pets to replace children.

This phenomenon is familiar from biology - the common cuckoo goes to much greater lengths to imitate its host, but myrmecophily by lycaenids presents a closer parallel. Many of these species interact with ants in a mutualistic way, providing services in exchange for food; but some have come to act as parasites or predators.

The situation you describe has much in common with ordinary brood parasitism. Even if willingly, the humans are allowing themselves to be supplanted at a reproductive level. The question with extinction, as in the wild, is whether there are refuseniks who harbor such backward, reprehensible, racist, perverse, inhuman, unthinkable beliefs in the supremacy of their own species that they stubbornly continue propagating as humans always did? And what will your new species do to help them go into the good night?

Answer 3

No, they can never supplant humans via mating. Worse they will likely go extinct themselves.

The more they breed the less desirable they become. They hey are creating a very strong evolutionary pressure to not be attracted to them, human mate selection should shift. Consider what happens once they make up a decent percentage of the population, Since human who are attracted to them stop producing offspring only those that are not attracted to them are passing on their genes, very quickly human mate choice should shift so they beautiful people are now the ugly people.

Worse they are going to be very vulnerable to disease and mutation. Sex as an adaptation persists because recombining your genes makes your offspring much more resistant to parasites and disease and it also allows deleterious mutation to be removed from the genome without the entire line going extinct. Since your creatures connote do this, they have very little genetic diversity, worse they should be suffering the same effects of persistent inbreeding, since deleterious mutations are going to build up in their genome. They are essentially asexual, and slow breeding large asexual animals are basically guaranteed to go extinct as deleterious mutations build up faster then they can be eliminated.

In animals this is actually discussd. This is called the Haldane's cost of selection dilemma, a species that can't reproduce quickly but also is not having recombination builds up deleterious mutations. there is a calculation for how fast they should go extinct But it dependent on their elective pressure and population number. With basically no selective pressure They should take about 6,000,000 generations for them to go extinct, assuming their genome is the same size as the human one. But that is assuming basically no selective pressure, but as I have pointed out they have some strong selective pressures on them which should drastically shorten that. predicting it accurately would be a PHD but 600-6000 generations or less is not unreasonable. for scale humans have about ~10,000 generations