Speciation in Evolution

[SezMe]

I'm not a biologist but I thought this article was interesting. I'd be interested in comments from those more knowledgeable than I.

 

[marplots]

It doesn't seem controversial to me, especially when you add extinction into the mix as a confounding factor. All it depends on is "soft" niches - so many available ways to live that survival doesn't depend on a particular ability.

My reading is that it's just another way of looking at what everyone already agrees on. But I'm an amateur here and I await my betters and their comments.

 

[Gawdzilla Sama]

It doesn't seem controversial to me, especially when you add extinction into the mix as a confounding factor. All it depends on is "soft" niches - so many available ways to live that survival doesn't depend on a particular ability.

My favorite example is the zebra. One zebra may have a better pattern than others, but not be the fastest zebra in the herd.

(And, yes, I've heard of the various opinions about what function the stripes actually serve, it's just an example, not a definition.)

 

[jonesdave116]

I think the controversial part of the hypothesis is the 2 million years per speciation event, regardless of generation time. They're effectively saying that a mosquito will throw up a new species, given geographical isolation, no faster than an elephant. Not sure about this.

 

[ryu238]

...it's ironic, we've told creationists that evolution is partly random...

 

[marplots]

I think the controversial part of the hypothesis is the 2 million years per speciation event, regardless of generation time. They're effectively saying that a mosquito will throw up a new species, given geographical isolation, no faster than an elephant. Not sure about this.

That's a nuance I didn't pick up on, but I could see why generation-time wouldn't necessarily make a difference. If mutation rates (here I mean successful, species-defining types of mutations) are relatively slow, then the generation-time would impact the spread of the mutation, but the overall rate could still be the driver - especially if it takes 2 million years for a suite of chance mutations to have a significant impact.

In the extreme (for illustration), say there's only one worthwhile mutation every million years. Then, it doesn't matter if you are a mosquito or an elephant, the event is going to impact your species the same, regardless of how fast you breed. So long as your generation-time isn't on the order of hundred thousand years between births.

This seems like a math question to me. Still, I would like to hear more in the way of explanation/explication.

 

[Beerina]

So basically the vast majority of DNA changes are little quirks that don't affect the organism, and that a buildup of these is what causes the speciation (DNA is no longer compatible) milestone to occur.


I always thought sexual reproduction, although somewhat controlled (compared to random neutrons & friends) did the vast majority of changes, and that these could build up at the DNA level as well (e.g. you aren't just safely touching some quasi-variables leading to, say, leg length). Sexual reproduction is magnitudes faster in scouring the evolutionary fitness gradient descent space, which is why it itself evolved, leaving "only" chance nuclear or chemical copy error mutation far behind in the dust.

 

[Swordfishtrombone]

As is so common in these sorts of articles, if you only read the title and short blurps, like here "Researchers build the world’s largest evolutionary tree and conclude that species arise because of chance mutations — not natural selection.", you get the impression that what is being proposed is totally radical, and about to turn everything you know on it's head.

Of course, when you read further, and actually find out what it's about, you find that what is being proposed is far more modest, but still interesting.

So essentially, one point they are making as if it was new is that while geographical factors and differing changes in the separated populations driven by natural selection can start the process, that these changes don't alone lead to speciation, but random mutations acquired over time in the separated populations gradually make them genetically incompatible, and incapable of interbreeding.

I thought this we already knew? At least this is how I've understood speciation to work.

So what is new is the assertion that for this sort of a speciation event to reach it's conclusion, it takes about two million years, on average, regardless of what species we are talking about.

And that IS really interesting, if true.

 

[Lowpro]

I think the controversial part of the hypothesis is the 2 million years per speciation event, regardless of generation time. They're effectively saying that a mosquito will throw up a new species, given geographical isolation, no faster than an elephant. Not sure about this.

Not quite how to interpret that. The base rate of mutation can best be predicted at the same rate between all species. That's just the chemistry of it. If you're at a HWE (sans noxious mutations) then yes, elephants and mosquitoes will alter their genes through mutations at the same rate.

But HWE doesn't really occur in reality. None of this really is controversial. Sewell Wright pretty much figured all this out so I'm surprised that anyone could find much controversial here. All Hedges did was expand the Sewell Wright model. Speciation is a genetic quality and natural selection influences the genes that get to play in the sandbox. Even without any obvious natural selection (ie at HWE) you'll still have mutations enough to have a different species given time.

So wherever you are Dinwar and Kotatsu, what's your thoughts on this article? Clickbait?

 

[barehl]

I'm not a biologist but I thought this article was interesting. I'd be interested in comments from those more knowledgeable than I.

The 2 million year clock seems about right for gene drift. That would be about 100,000 generations for a species with a 20 year generation. That would work for humans but not for rats or horses.

 

[Trakar]

So how does this research accommodate ring species?

 

[Craig B]

That's a nuance I didn't pick up on, but I could see why generation-time wouldn't necessarily make a difference. If mutation rates (here I mean successful, species-defining types of mutations) are relatively slow, then the generation-time would impact the spread of the mutation, but the overall rate could still be the driver - especially if it takes 2 million years for a suite of chance mutations to have a significant impact.

Is it radical mutation that is the main driving force of evolution? I thought separation of populations within the same species played a leading role. Some S American tortoises found their way to the Galápagos Islands and new species gradually evolved there.

The evolution did not require the S American tortoises to await a radical gigantism mutation for the species now on the Galápagos to be formed.

 

[MG1962]

Is it radical mutation that is the main driving force of evolution? I thought separation of populations within the same species played a leading role. Some S American tortoises found their way to the Galápagos Islands and new species gradually evolved there.

The evolution did not require the S American tortoises to await a radical gigantism mutation for the species now on the Galápagos to be formed.

I was wondering the same thing about the same example. Every isolated island a species of tortoise has made it to has seen some variation of gigantism occur

 

[The Shrike]

"Consider Hawaii’s honeycreepers. The speciation clock started once the birds migrated to a new island and began to accumulate random mutations. The vast majority of these mutations were neutral, having no effect on the birds’ appearance or behavior. "

There's a bit of a rub here as well. A mutation is neutral if it has no particular bearing on fitness, i.e., lifetime survivorship and reproduction. There are all sorts of mutations that could do something to affect phenotype without affecting fitness. If the thing done to the phenotype leads to reproductive isolation (e.g., a change in a bird's song to which females from the "parent" population don't respond), then yes, speciation can be driven by genetic drift in the absence of strong selective pressure.

 

[marplots]

Is it radical mutation that is the main driving force of evolution? I thought separation of populations within the same species played a leading role. Some S American tortoises found their way to the Galápagos Islands and new species gradually evolved there.

The evolution did not require the S American tortoises to await a radical gigantism mutation for the species now on the Galápagos to be formed.

I was wondering the same thing about the same example. Every isolated island a species of tortoise has made it to has seen some variation of gigantism occur

It's the same thing, isn't it? If we never separate a subgroup, then any neutral or positive mutations permeate the entire population. You still get different species, but they are only different through time, not contemporaries.

However, all separated subpopulations moving in the same direction (the island-separated tortoise giantism) would argue against this, unless it was both a common mutation and something with a huge survival advantage.

I wonder what they have to say about animals that don't seem to evolve much over really huge blocks of time - Crocodiles over 200M years? The current explanations I've heard:
1) They did change, but there weren't any dramatic phenotype changes picked up in the fossil record - leaving immune systems and other targets instead. Don't know how I feel about this one. Hard to prove, I guess.
2) They have a mechanism to deal with mutations that is more powerful than the norm. Not sure about this either.
3) Their niche is so specific, it tends to extinguish change. Again, seems like something you'd have to prove, but this argues against the "mutation-driven" scenario, which would rely on weak niche influence.

Speculation is fun, but I'd like to hear from Dinwar.

 

[Dinwar]

People are surprised by this? This was stuff I learned as an undergrad, right along with how to prep fossils and how to identify the various phyla.

As for the rates, I'm not sure I believe it. There's some pretty interesting controversy over how to apply genetic data to the fossil record, and many studies that attempt to tie genetics to fossils have a poor understanding of calibrations in the fossil record (that's assuming they even look at fossil calibrations, which is often not the case). I take all studies where biologists say "Genes do this through time" with a HEAVY grain of salt, for the same reason anyone should take a paleontologist saying "Modern organisms do X" with a pretty heavy one.

Is it radical mutation that is the main driving force of evolution? I thought separation of populations within the same species played a leading role.

You can separate populations for a billion years, but if the genes don't change they'll still be the same species. Mutations are necessary to drive differentiation between the species. They don't have to be radical individually, but en mass small changes can have profound effects.

 

[MG1962]

It's the same thing, isn't it? If we never separate a subgroup, then any neutral or positive mutations permeate the entire population. You still get different species, but they are only different through time, not contemporaries.

However the common wisdom seems to be, the bigger the base population the slower mutations have an effect over the entire population. Islands present a fascinating laboratory for genetic variation because it is highly likely the entire genetic make up of a species is not represented. So in theory mutation and the rise of new species should be a lot faster in such and environment. But if I am reading this article correctly. That is not the case at all.

 

[marplots]

However the common wisdom seems to be, the bigger the base population the slower mutations have an effect over the entire population. Islands present a fascinating laboratory for genetic variation because it is highly likely the entire genetic make up of a species is not represented. So in theory mutation and the rise of new species should be a lot faster in such and environment. But if I am reading this article correctly. That is not the case at all.

I see what you mean about bigger base populations, but I assume that's swamped by the two-million-year step. Provided, of course, that 2MY is a reasonable number in the first place.

 

[Dinwar]

The real issue here isn't "Is this true or not?" It almost certainly is true that mutations play a huge role in determining the evolutionary history of a species--in some cases. In others, the niche will play a more significant role. It's a question of which is dominant in the taxa in question.

Take marine predators, for example. Icthiosaurs, dolphins, sharks, and submarines all have the same body shape, despite being very, very different taxa (and one group not being biological at all). That's because of very serious physical constraints--fluid dynamics demand that if you want to move fast through the water, you will be shaped in a specific manner. In contrast, browsing is pretty easy, and as long as you have a way to get the plant matter into your digestive system you can have any morphology you wish. So it's pretty clear that there are multiple ways for evolution to work, not just the One True Method.

 

[SezMe]

People are surprised by this? This was stuff I learned as an undergrad, right along with how to prep fossils and how to identify the various phyla.

Lighten up, Dinwar. I didn't say "surprised", I said I found it interesting.

I went to a high school where "evolution" didn't exist. And my entire academic career was in math and the physical sciences; I had no further biology. I do try to stay informed of the life sciences but it's not easy to keep up. Posing questions here is an excellent way to get an exposure from a variety of sources.

I'll make you a deal. I won't poo-poo your lack of knowledge of numerical approximation if you don't poo-poo my lack of expertise in the life sciences. OK?