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:
- The cell dies. The DNA is like the computer program that runs a cell and if that breaks, the cell cannot function and dies.
- 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.
- Mutations... lots and lots of mutations.
- 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:
- Two individuals mate
- They die
- Through a contrived and icky path their DNA becomes the mating organs of other individuals
- 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.