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mothmvn t1_jbj3qzr wrote

Reply to comment by lunas2525 in Is there a fertile creature with an odd number of chromosomes? by TheBloxyBloxGuy

You have it a bit backwards: evolution doesn't advance through hybrids, it advances through the best-adapted individuals surviving. Like a lungfish with a mutation that gives it slightly more developed limbs, or slightly better chances at surviving outside of water. This lungfish mates with another, overall average lungfish, and their children may have that one cool parent's mutations with better access to a world most lungfish don't visit.

Repeat to the power of N (even bigger limbs, even better lungs, proto-claws, proto-fur, etc). If it gives the creature an advantage over the other members of its species, the creature has a better chance of making babies before dying, and the trait is passed on more often. There is no objective measure of what's a better or worse trait, of course — whales evolved back into water because that, too, was advantageous in a way.

Hybrids don't really have a role in the typical evolution pipeline, is the point. Sorry if this is old news, of course, just figured there's no harm in writing it out.

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Tyrosine_Lannister t1_jbjcvyo wrote

I feel like this ignores the common ancestry of all life, though.

Like, sapiens-neanderthalensis "interbreeding" is a great example.

We diverged for a while, likely just due to geographic isolation, then re-crossed, and now a significant fraction of people are "hybrids", even if neanderthal proper aren't around anymore.

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almightySapling t1_jbkhsfx wrote

Was there a period where sapiens and neanderthals couldn't interbreed? I guess what I'm trying to understand is what formally makes them different species in the first place.

Seems to me that "hybrids," as a concept, have less to do with biology and more to do with our arbitrary classification of it.

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Rather_Dashing t1_jcym0rf wrote

Species is just an arbitrary classification. Interbreeding is only one factor used to determine what is a species. Its thought that only female neanderthal human hybrids were fertile and not males, so that one justification for considering us seperate species. Just how likely an offspring is to be fertile could also be taken into account. If two species have to breed a million times to produce 1 fertile offspring, it doesnt mean the two are the same species, there is never going to be considerable gene flow between those two groups.

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ukezi t1_jbknqm4 wrote

Our current definition of different species required then to not be compatible and apparently sapiens sapiens and sapiens neandathalensis were compatible at least to a certain point.

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ScipioAfricanisDirus t1_jblw9du wrote

There isn't really one authoritative "current definition" of a species the way we're taught in lower-level science courses, at least not one so clear-cut and universal. If you ask a molecular biologist, a botanist, a zoologist, an ecologist, a geneticist, and a paleontologist to define a species you'll get six different, and sometimes contradictory, answers. Hell, if you ask two biologists in the same field you'll occasionally get competing answers.

These different definitions are called species concepts, of which probably the most common is the biological species concept. This is the one that you're referring to, which defines species based upon reproductive isolation. But it's not a perfect nor universal definition; it's entirely useless for asexual organisms, isn't informative in cases of horizontal gene tranfer, can't be directly tested in certain circumstances like when dealing with fossil species, and even breaks down with extant sexual populations in situations like ring species or many cases of hybridization (which we're learning is a lot more common and complex than previously thought). Other species concepts work better when dealing with asexual populations, or extinct groups, or when working specifically at the genomic level.

Most biologists work within the framework of whatever species concept best fits their field day-to-day as a shorthand but recognize there's a lot of nuance to the biological reality. That is to say, it's not as simple as can interbreed or can't.

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peteroh9 t1_jbj8j0b wrote

But if the number of chromosomes changes as species evolve, there would most likely be a point where an organism with one number of chromosomes is mating with one that has a different number of chromosomes.

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Techiedad91 t1_jbjcc69 wrote

Are you referring to Speciation?

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Nick-Uuu t1_jbjhj27 wrote

Speciation isn't one and done, it's a shift in the average of a whole population, so this would be part of it but definitely not the norm

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Rather_Dashing t1_jcymabj wrote

Yes, in fact there are plenty of species which have differing numbers of chromosomes within that species. All different chromosome numbers mean (if everything else is the same) is that there is slightly higher chance of genetic abnormalities and the offspring is slightly higher likelihood of being infertile.

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Nick-Uuu t1_jbjhc1h wrote

Evolution is a complicated thing and hybridisation shouldn't be brushed off. It's quite common in more closely related animals, which leads to different results than random mutation. It's likely what you said was taught to you at one time but evolution is one of those things that's always overly simplified and it annoys most biologists I know.

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DaSaw t1_jbk1n11 wrote

Red wolves, for example, may be a stable hybrid of grey wolves and coyotes.

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lunas2525 t1_jbky25n wrote

Exactly just like guppies and Betta are very different from natural and in the case of guppies there are like 4 or 5 species that they can cross with endlers, swordtails, mollies, platty, guppies can all interbreed with some complications some hybrids are too big for the mother to birth. Eg these are not viable Platy male and guppies female... Mollies male and female guppies, endlers female to anything except endlers. Where as swap the gender and you can hybrid.

And like some one else said hybridization is not something to separate from evolution as it can give leaps towards bigger changes if they are not viable they die if they end up beneficial to survival hybrid lives to mate and join the gene pool for either a whole new species or or in the case of what we believe happened to neanderthal proto humans out bred and some hybridization occured so basically their genes got poured into the pool and the hybrids diluted down

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lollerkeet t1_jbj861j wrote

Hybridization brings genetic diversity. Lots of small differences to choose from.

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