Would mutated, parasitic 'metahumans' solve proliferation problem in a post apocalyptic world?

Question

Many years after the worldwide nuclear holocaust, most animals undergo mutation, and are turned into savage and cunning predators built to kill. It is an extremely chaotic and dangerous world, and what is left of the human race is now the slyest of all. The following is the reproductive cycle for the 'metahuman':

Phase 1: Mating begins between two mature 'metahumans' of opposite sex.

Phase 2: After copulation, both parties die from guaranteed acute cardiac arrest and rot at an accelerated rate.

Phase 3: The pungent smell attracts other animals to feast on them.

Phase 4: The retroviruses carrying meta-human DNA find their way into the digestive tracts of the hosts. The virus has developed resistant to the strong acidic content of the hosts' stomachs and can temporarily disable the host's immunity.

Phase 5: The animal's droppings house colonies of the retrovirus which become food for other 'metahumans'. Believe it, this is survival instinct at its finest!

Phase 6: The retroviruses quickly work their way into the blood stream and turn some cells into sperm and eggs, which come with a complete set of working reproductive systems.

Nature may have turned against us, but humanity will find a way! I was wondering if this scenario could be realistic?

Answer 1

I have conducted some research, and here is what I can come up with:

Thanks to Phase 1, since humans die shortly after mating, this will greatly reduce their average life expectency. Which in turn would greatly hurt human productivity since shortly after reaching adulthood they die.

The virus has developed resistant to the strong acidic content of the hosts' stomachs

There are bacteria that do pretty much as you described in real life so this is completely reasonable.

The animal's droppings house colonies of the retrovirus which become food for other 'metahumans'. Believe it, this is survival instinct at its finest!

The plants thank you for your donation of nutrious droppings. By the time the baby is born (assuming 9 months), the droppings likely already have been absorbed by the dirt, washed away by the rain or other post apocalyptic weather, or eaten by insects (ever seen an apple that has been outside on the ground for a week?). Your baby likely will never be able to get them. Also if the droppings contain concetrated nutrition then it will be robbing the fetus of nutrition that it needs to grow.

Lots of DNA

I am assuming that the retrovirus in Phase 4 is produced during Phase 1 and it contains the genetic material of both parents so that it can create sperm and eggs in Phase 6.

Note that the retrovirus can either have a full copy of the parents' genome or only half of each. If it has a full set then the sperm and the eggs can have a greater variety of combinations, which is extremely valuable since the parents will only get to mate once, and you want as much genetic variety passed on to the next generation.

As such a single human has approximately 3 billion base pairs. Since your virus contains two humans worth of dna it will need to be able to store 6 billion base pairs. The largest virus I could find has 250 thousand base pairs. This means you are going to be trying to store 24,000x times as much material into a virus than typical.

Size matters

A large virus can reach 250 nm in size, while the nucleous of a cell is 3,000-10,000 nm (and a human red blood cell is 9,000 nm). Odds are your virus will be closer in size to a nucleous of a cell in order to store the shear volume of DNA it is trying to carry. Viruses typically infect a cell and have the cell produce lots of copies of itself till the cell bursts. With a virus so large an infected cell likely will only be able to make a single copy of the virus, or two eggs and two sperms before it bursts. However, a single copy is not good enough. Virus only can infect a cell once, since it injects its only copy of its DNA into the host cell. This combined with a single copy results in it not ever being able to make more of itself.

Phase 7

Lets put the cell size issues aside and look at the animal size issue. You got lucky the creature you infected was a carrion eater and has successfully produced a ton of eggs and sperms. Human fetuses have a 9 month gestation period, and need a host that can carry a fetus to term before it dies. Also you will need to either infect multiple carrion eaters in one go, or the one carrion eater needs to be capable of delivering multiple metahuman babies before dieing. That rules out a number of carrion eaters, since they are birds and the weight from the fetuses would eventually prevent or hinder their ability to fly and thus they will die from starvation as the fetus(es) sucks the life out of them. There are so many small (insects) to medium sized (coyotes) carrion eaters out there that odds are they will get to the corpses first before a large enough carrion eater makes it to the scene. If this happens then your metahumans will fail to spread their species further. Since even a coyote would likely not be big enough to carry a fetus to term.

Phase 8

Lets assume that the carrion eaters in your post apocalyptic world are much larger and can handle the multiple fetuses long enough for the babies to be born. Well congrats you have triplets! Unfortunately you now have babies without any parents. Humans need a lot of help growing up. They lack defenses and can easily be picked off by a post apocalyptic predator. Human babies like other mammals rely on milk from their mothers to feed them, but unfortunately mom died during conception so no milk.

Ideas

With all this said, you might want to upgrade your thing from a virus into a flesh eating bacteria that can cocoon its victims. That may deliver what you are looking for. The flesh eating bacteria converts the host essentially into an incubation chamber for the fetuses and near the end it turns what is left over into a nice juicy paste that the baby can easily consume after being born to give it a quick jump start rather than relying on nutricious dropping.

Second idea is to skip the virus and have fertilized spores being produced during phase 1, which act like seasoning on the metahuman corpses. The spores get into the intestines and leach off the nutrition that the host eats until they get too large. At this point the host is likely rather weak and the embryos then devour their host from the inside out, where hopefully they get enough material during that last phase to be properly born.

Answer 2

No, this is not realistic, and everyone will die

Summary: It is not realistic, and you left out the creation of new life, meaning that soon everyone dies.

You asked for "reality-check". And you see, I have a policy...

Many years after the worldwide nuclear holocaust, most animals undergo mutation, and are turned into savage and cunning predators built to kill.

No, that right there is not realistic at all. Yes I know that the "radiation causes mutations that leads to things being evil" trope is very popular and common.

...and it is as far from realistic as it gets. And it does not get any better that you say "many years" because the potency of ionizing radiation diminishes rapidly. "Half-life" is probably the most misunderstood quality of radioactivity.

Let me explain how gene damage from ionizing radiation works...

This is radiation

Radiation is like bullets. These are bullets that are all around you, all the time, because visible light, infrared, radio, gamma rays, cosmic radiation.... all of this is radiation.

Normally there is only a small amount of radiation-bullets hitting you, and most of those are so weak that they "bounce" off of you. That is so called "non-ionizing radiation". There are a few bullets that actually hit you and do a bit of damage. This is so called ionizing radiation and this is what we normally talk about when we use the moniker "radiation".

If these radiation-bullets hit your DNA, the double helix may break. It may break either one strand, or both. Normally this is not a problem because we have DNA repair mechanisms (the subject of 2015 Nobel Prize in Physiology or Medicine). The DNA repair patches your DNA back together. And it is a good thing too because your DNA breaks a lot... 10 000 to 1 000 000 times per cell and day.

Sometimes, the repair do not go well. Then the DNA stays damaged. One of two things can happen:

1. The cell dies. The DNA is like the computer program that runs a cell and if that breaks, the cell cannot function and dies.
2. There is a mutation. The DNA is put back together again, but incorrectly.

But here is what most people get wrong about mutations: one error in one gene in one cell is a microscopic change. It is like one bit in a computer program, installed on one user's computer gets flipped. This may make that particular installation of the program malfunction and stop working. Every other program on everyone else's computers are fine.

The kind of "mutations" you are talking about — aggressive behaviour — is not a mutation. That is acquiring a new trait. That is evolution. Getting a new trait is as if someone took a large part of the computer program and completely rewrote it. And then everyone installed that new program. More on that in a moment.

What happens when you have nuclear devastation and there is lots of ionizing radiation around is that you massively increase the number of radiation bullets that fly about and break your DNA. Then the DNA repair mechanisms can get overwhelmed and cannot repair DNA fast enough. For the most part, this means that cells just plain die. However in a few cases, there may be enough mutations on the microscopic level that you might get a change in how the cell works. Most commonly this results that the cell becomes cancerous. That too is very bad for health and the victim usually dies.

This is evolution

Evolution — that is to say when a species develops a new trait (such as "aggressive behaviour") — is driven by two things.

1. Mutations... lots and lots of mutations.
2. Survival of the fittest.

In order to get a new trait, such as "aggressive behaviour", then you need many genetic mutations. And they must all fit together. And they must not kill the individuals that got the mutations.

Then the mutated individuals must procreate, and their offspring must survive, and do so better than their contemporary siblings.

The problem with your premise

...is that you assume that many different species, got the lots of genetic mutations, which in turn gave rise to the exact same new trait in all of these species, and that they all survived, and that they all became more fit because of this new trait.

...which is complete nonsense from a reality check perspective.

So just forget it. You are not in the realm of realism. The "radiation makes aggressive monsters" trope is fairy tales. You can just forget any aspirations of realism and reality check because the very premise is not realistic at all.

Hence the burning question. Assuming we are in the realm of fairy-tales:

Is that reproduction cycle realistic or even viable?

Well if could have been "realistic" within the stated premise since we have to postulate magic and/or fairy tale logic anyway. But it is not even viable because you have left out one very important aspect of this cycle of reproduction: the birth of new individuals.

Read again what you wrote:

1. Two individuals mate
2. They die
3. Through a contrived and icky path their DNA becomes the mating organs of other individuals
4. Go to 1.

Where is the creation of new life? You left that bit out.

So it is not only not realistic, even in the realm of fairy-tale it only results in death, not new life.

_{So yeah, the entire lecture on radiation is for naught but I just had to rip the throat out of that premise because I so much hate it. Radiation = evil is just the Boogey Man of the 21st century.}