How does a genetic mutation reach critical mass to become a new species?


It would seem that genetic mutations are random events. How does such a random event reach enough critical mass to become self-sustaining?

In: Biology

There really isn’t a “critical mass” needed to make a new species – this isn’t leveling up in a video game. It’s just a collection of changes over time.

Most mutations have no effect – they’re neither positive nor negative, so they can build up over time, particularly for small population sizes.

Finally, it’s worth remembering that “species” is a human construct, much like “race”. There is a lot of grey area in classification of both.

“Species” is a nebulous term. Scientists usually define it as the point when two populations of animals can no longer breed with each other, but there are other definitions.

Further more, there’s no “critical mass” of mutations; I am different from my parents, and they’re diffferent from their parents, and so on. At one point, my many-many times great-grandfather was an ape-like animal, and before that, a lemur-thing, then a rat-thing, then a lizard-thing, then a fish-thing and a slug-thing and, all the way back, a single microbe. There is a completely unbroken line of descent from the first life all the way to me, with hundreds of species in between, and yet every single one of my forefathers was the same “species” as their immediate parents.

If the mutation is truly beneficial the number of individuals with the characteristic will grow up in geometric progression, slowly gaining advantage against the individuals that don’t posess the characteristics until it reaches a point that they won’t be able to share the same habitat and then the population with the mutation will quickly explode in numbers and those that don’t have will either leave of die.
But that doesn’t mean that a new species was born ye, just that the characteristic was selected because of the benefits it brings. For a new species to be born it is required some kind of geographical isolation that prevents two populations of the same species mating with each other, then during a long period of time a big number of mutations will happen until the population can’t produce a fertile offspring with the species that originated themselves.
*A new species is ONLY considered a new species when they can’t produce fertile offspring with other similar species or it’s ancestral specie, just with each other.*

This isn’t ELI5 level reading, but this may help. This idea in evolutionary biology is basically the how-to for your question. The [Hardy-Weinberg Principle ] is a sort of list of ways genes can become more common in a population, eventually leading to new species. In the simplest terms, there are some conditions that make new genes more likely to catch on. For example, imagine a lone tortoise, laden with eggs, is washed out to sea along with some floating vegetation (hurricane or flood washout). She makes it to an island where she lays her eggs. If the island has no other tortoises, the ones who hatch are all siblings, and share a lot of the same genes, about half. So whatever genes the mother had, even her rare genes, are now the dominant type. According to the H-W principle, this small population (or genetic bottleneck) is one of those conditions that can lead to a new species. There are other conditions, of course. I hope this helps.