Butterfly unlocks evolution secret

[C1ay]

From the BBC:

Why one species branches into two is a question that has haunted evolutionary biologists since Darwin.

Given our planet's rich biodiversity, "speciation" clearly happens regularly, but scientists cannot quite pinpoint the driving forces behind it.

Now, researchers studying a family of butterflies think they have witnessed a subtle process, which could be forcing a wedge between newly formed species....

For speciation to occur, two branches of the same species must stop breeding with one another for long enough to grow apart genetically.

The most obvious way this can happen is through geographical isolation.

If a mountain range or river divides a population of animals for hundreds of generations, they might find that if they meet again they are no longer able to breed.

But geographical isolation is not enough to explain all speciation. Clearly, organisms do sometimes speciate even if there is no clear river or mountain separating them....

More.....

A very interesting article illustrating progress via the scientific method.

[Biochemist]

A really interesting post, C1. I like the flavor of the article, mostly because it acknowledges the limits of our current understanding.

It does start out with a false premise (we must have speciation because we have species) but the rest is pretty fair. I happen to agree with the conclusion, but this premise is weak.

It also brings up more questions than it answers. We have what appears to be a pretty good example of potential sympatric speciation, but there is no identifiable environmental force that would drive this particular selection. We have a tendency for butterflies with different markings to breed with matching butterflies, and weak offspring when the two subspecies interbreed, but no obvious reason why the markings were differentiated in the first place.

The superficial view of this information would suggest that a new species is arising in the absence of selective pressure, and may indeed grow into a reproductive isolate without it.

This might be a meaningful counterexample to the tenets of natural selection. If a species can actually generate a reproductive isolate in the same geography without selective pressure, what drove the change?

[ThickSet]

I'm having trouble expressing this clearly so I ask you folks to help me here. I'm on a lot of meds.

The butterfly observation is nothing new. The reason 'why' is nothing new. 'How' it happens is nothing new. What we are discussing here applies to everything from butterflies to brains: evolution occurs with genetic accidents gaining a foothold due to environmental conditions favouring the particular mutation. Species adapt to their surroundings through survival. Hence tribalism, the vagaries of butterfly (and human) nature.

Come back.

[Biochemist]

Originally Posted by ThickSet

...The butterfly observation is nothing new. The reason 'why' is nothing new. 'How' it happens is nothing new. What we are discussing here applies to everything from butterflies to brains: evolution occurs with genetic accidents gaining a foothold due to environmental conditions favouring the particular mutation. Species adapt to their surroundings through survival. Hence tribalism, the vagaries of butterfly (and human) nature....

TS-

WE have run a number of threads where I have underlined that the mutative mechanism underlying much of the thinking within speciation is open to question. The basic science support for it is mostly conjecture, not evidentiary.

It is not supportive to repeat standard dogma (like "we know x" and "we know y") when the topic is actually that we most certainly do NOT know x or y.

The article that C1ay posted was a really good example of things to question about our current thinking/presumptions about natural selection. And it says absolutely nothing about a mutative mechanism. This appears to be an example of sympatric speciation in the absence of an environmental pressure. Just take it as the data point that it is. This evidence may well be starkly at odds with the standard thinking on the subject.

[ThickSet]

Hi BioChem - many thanks, you are expanding my mind again.

I used the term 'tribalism'. Is the butterfly wing-marking not the same thing as tribalism, only manifested differently? Is it fair to say (generally) all animals tend to band together into smaller units. (I have an engineering background, so biology is out of my experience, and I speak without authority) I always thought evolution was so darned obvious I automatically accepted it. But then again, a lot of people use this same kind of approach to accept 'God' (ouch).

I'll try this again. It's always seemed obvious to me, reflecting on human nature, how this whole evolution thingy works - it is a requirement for all 'living' organisms to experiment. The driver is our very deepseated 'ego' = f(survival, domination, accident, environmental, and so on).

[Biochemist]

Originally Posted by ThickSet

Is the butterfly wing-marking not the same thing as tribalism, only manifested differently? Is it fair to say (generally) all animals tend to band together into smaller units.

It is an interesting idea, but evolutionary biologists tend to think of tribalism as something that would be driven by a selective process that drove participants toward that sort of behavior.

The problem is that these "obvious" assessments often are "good from far, but far from good" when you dig into the details. Since you are an engineering sort, it is a little like the initial surprise and discomfort that so many felt with the dual slit experiments in the early days of quantum physics. Some of those results just did not make any sense. But they happenned to be true.

In the case at hand, there was no observable pressure for a subset of the animals to act separately. If there was no pressure to do so, and the set of animals did, it is not supporting the notion of natural selection.

Really good examples of natural selection are pretty rare. There are some, but most examples are assumed, not demonstrated. Ditto with the notion of a mutative mechanism to expand the gene pool. It is assumed, but not demonstrated.

Thanks for the interest. And welcome to Hypography!

[MortenS]

I hope you mean that good examples of speciation by natural selection are rare, not that good examples of natural selection are rare, Bio...

[Tormod]

Originally Posted by Biochemist

It does start out with a false premise (we must have speciation because we have species)

Bio, this is not a false premise. We would not have species without speciation. When discussing evolution we need to talk the language of the theory. You may not agree that speciation happens but then you should also not use the term "species", since it *does* imply that speciation occurs to separate them.

We have the fossil record and also DNA testing as evidence that speciation has occured. What we don't have as of yet is speciation under observation - which is to be expected because these things take time.

For those not into the evolution theory, here is a good starting point:
http://evolution.berkeley.edu/evosit...eciation.shtml

[Biochemist]

Originally Posted by Tormod

Bio, this is not a false premise. We would not have species without speciation. ..

Actually, T, I do agree that speciation happens. But I still think this is still a false premise.

The specifics of speciation are that species come from other species. I do not, however, think that it is obligatory to assume that species come from pther species just because multiple species exist. It is the evidence of the process (e.g., genetic drift, etc.) that supports speciation, not the existence of many species.

Insidious assumptions like these drive lots of false association and false causality as well.

[Biochemist]

Originally Posted by MortenS

I hope you mean that good examples of speciation by natural selection are rare, not that good examples of natural selection are rare, Bio...

MortenS- I did mean that good examples of natural selection are rare. A good example would show several elements:

1) a preexisting species
2) a preexisting stress on the species
3) an adaptation that was preferred in response to the stress
4) irreversibility of the adaptation

If selection drove speciation, we would add a fifth (for sexually reproductive species): Reproductive isolation.

Point #4 above is particularly rare in posited examples of natural selection.

We actually have very few examples of the above for sexually reproducing species. We have lots of apparent examples in bacteria, but even some of those examples (like acquired drug resistance via episome transfer) can be interpreted less like natural selection and more like a feature of the species.

I am not asserting that natural selection does not occur. I am asserting that the direct support of it is not as pervasive as some presume.