Why are some mutations, like additional limbs or more than 50 chromosomes, are just not possible for humans to have?
In: Biology
Extra limbs is actually a mutation that can and does happen. I assume that you mean a fully formed and functional extra limb, however. That’s not just some random mutation in a single gene somewhere. I’m no expert, but it would take perhaps dozens or hundreds of genes all mutating in exactly the right way at exactly the same time to get a fully formed and functional limb.
Short of that, in the best case scenario you’re going to have a malformed appendage that’s completely useless. More often than not it’s going to be in the way and cause you a lot more harm than good. This reduces your chances of passing your genes along and so future generations don’t have the opportunity to perhaps mutate another gene that improves the limb’s function.
And that all neglects the fact that the human body is not equipped to host another limb anywhere else on the body. Beyond just the limb, there are dozens more required changes. Support structures for the limb to attach to, etc.
So like others have mentioned, your question is based on false assumptions. These things can and do happen, but they’re detrimental to whoever has them and so the mutation does not propagate.
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