Walking Before Flying

An anonymous reader writes "BYU biostaticians report in Nature their genetic analysis of the insect, known as the 'walking stick', which apparently gives a contrapuntal example of reversible evolution. Called Dollo's Law, the principle holds that the same evolutionary pathway can never be backtracked, because of random mutations. But this insect class first had wings, lost them, then got them back again. So what's next for some humans: a happy return to dragging their knuckles?"

Comments

Contrapuntal?

[MacAndrew]

Gee, I don't think I've ever heard the word contrapuntal. Thank you, another small step in the evolution of my vocabulary. :)

Re:Contrapuntal?

[Alrescha]

The last popular use of this word was circa 1965, by Tom Lehrer:

So Long Mom (That Was The Year That Was)
(AKA The World War III Folk Song)

So long mom, I'm off to drop the bomb
So don't wait up for me
But while you swelter down there in your shelter
You can see me... On your TV...
While we're attacking frontally
Watch Brink-e-ly and Hunt-e-ly
Describing contrapuntally the cities we have lost
No need for you to miss a minute
Of the agonizing holocaust! Yeah!

Little Johnny Jones he was a U.S. pilot
And no shrinking violet was he...
He was mighty proud when World War III was declared
He wasn't scared no sirreee...
And this is what he said on
His way to Armegeddon...

So long mom, I'm off to drop the bomb
So don't wait up for me
But though I may roam I'lll come back to my home
Although it may be... a pile of debris..
Remember mommy I'm off to get a commie...
So send me a salami and try to smile somehow...
I'll look for you when the war is over:
An hour and a half from now!

A. :-)

Re:Contrapuntal?

[gi-tux]

You obviously aren't a musician or fan of music. Bach and many others of his time frame wrote contrapuntal music or music based on counterpoint.

"Return" to dragging knuckles??

[Shadow2097]

Apparently, whoever wrote that never met any of the jocks at my high school! ;-)

Back on-topic, it does open up a whole lot of new possibilities as far as evolution goes. The evolutionary tree that is so commonly displayed in high school (and some higher-level) biology books might need some major rethinking.

-Shadow

Re:"Return" to dragging knuckles??

[billn]

So what's next for some humans: a happy return to dragging their knuckles?"

Or they've never encountered large roaming tribes of 'Jackass' fans.

rapping knuckles...

[KDan]

Unlikely. The genetic difference between an insect leg and insect wing (according to these articles, see Google News for a lot more sources that came out with this days ago) is very slight, the result of a single set of genes that switch between a leg and a wing. The difference between hairy quadruped apes and intelligent biped humans is a bit more pronounced... and there's no evolutionary pressure to make us devolve back to being quadrupeds (apart from that coming from the direction of good ole' Dubya).

Daniel

Re:rapping knuckles...

[KDan]

Erm, I meant dragging knuckles of course.

*kicks self*

Daniel

Re:rapping knuckles...

[elakazal]

I was under the impression that limbs and wings were developmentally distinct structures, and that wings had not developed out of legs or vice versa. Could be wrong...it's been a little while since I had entomology.

Re:rapping knuckles...

[KDan]

That was part of one of the articles I read about this: They said that the same genes control whether wings or legs are well-formed, so when the wing is switched off, the genes in it are still protected from too much mutation until the wings are switched on again.

Then again, I'm by far no expert on the subject...

Here it is: http://www.newscientist.com/news/news.jsp?id=ns999 93269.

Researchers assumed wings could not come back once lost as the genes needed to create them would mutate beyond repair once the wings disappeared. But Whiting says there is evidence from the fruit fly Drosophila that the same genes contain instructions for forming wings and legs.

If the same were true for stick insects, there would be an evolutionary pressure to stop wing genes from mutating, even in the insects that did not have wings. Those genes could then be turned back on in the future.

Daniel

So maybe now...

[phagstrom]

we can learn the answer to the puzzle:

if a fly couldn't fly, would we call it a 'walk'?

Underlying assumptions

[scistu]

I guess this guy has looked at mutations in the stick insect genome and made inferences about the phylogenic tree relating the species. The underlying assumption in these sorts of approaches is known as the infinitely many sites assumption. This says that a mutation can only happen once in any place on the genome and once it has happened it cannot mutate back. This assumption, although reasonable in most cases, may not be valid here. It would be nice to know how much information was used from the genome in order to get an idea of the validity.

Laws of probability

[xayide]

From the article:

Dollo's Law ... is also known as the Law of Irreversible Evolution--which basically states that organisms cannot re-evolve along lost pathways, but must find alternative routes (because the same fortuitous train of mutational events, being totally random, will never repeat).

I was not familiar with Dollo's Law before reading this story, and I may be misunderstanding some nuance or other... However, if mutations are truly random, isn't it necessary that they at least have the possibility to recreate a lost pathway, no matter how complex?

Re:Laws of probability

[PD]

I don't understand why biologists thought that evolution could not repeat itself. Seems like if the environment is A, changes to B, then changes back to A, the organisms would also follow the environment in their evolution.

As supporting evidence, consider the large number of completely unrelated but similar appearing plants that live in the desert and look like Yucca. If multiple species can adopt a similar appearance in response to a similar environment, then why can't that happen within a single species?

Re:Laws of probability

[BCGlorfindel]

However, if mutations are truly random, isn't it necessary that they at least have the possibility to recreate a lost pathway, no matter how complex?

I believe it was more a prediction that if evolution operates as we expect, organisms would be unlikely to 'solve' an evolutionary problem the same way twice. It was not so much saying such an occurrance was impossible, but that it's occurance would out of keeping with the idea of evolution being pushed by random mutations.

That said, Dollo died in 1931, so modern discoveries like pretty much all DNA/genetic evidence wasn't available to him. I'm not sure here, but I don't think a lot of weight was put in Dollo's law anymore. Anyone out there know of reasons someone would even bother mentioning that their research contradicted Dollo's law?

Re:Laws of probability

[Tye_Informer]

So let me see if I get this straight. Dollo's law is more of a theory (unproven then and now set aside/ignored) that was misnamed? Outside of Biology, the requirements for a law are very precise. It is a theory until proven, and a law can never be broken. IANAB (I'm not a biologist) and have not really studied anything in that field since college, but I am a scientist.

Every day I base decisions on theories that have been around since I before I was in school. I have confidence that they are valid along the entire range that I operate in. This does not make any of these theories into laws! As a scientist I must accept that at any time one or more of my precious theories could be proven false and thrown out. I'll admit that I am attached to some of the theories and would be amazed if they were ever disproven. I would probably be in mourning for a while. (sort of) There is even a possibility that I would have to change fields because I am allready set in my ways and could not make the change. That said, they are still theories and until they are proven I can not call them anything more. I would contend that by calling them a law I am no longer a Scientist, I am on my way to some cult leader ready to start the next Clonaid!

Re:Laws of probability

[xayide]

Mmmmm... convergent evolution... I'm under the impression that Dollo's Law refers to organisms evolving the exact same pathways to solve the same problem twice. When species evolve convergently, or even when one species re-evolves a trait, the same problem is usually solved in very different ways.
This site has the best definition that I was able to find, but I'm not sure how much stock I would place in its accuracy.

Re:Laws of probability

[BCGlorfindel]

I might be wrong here but I believe it was more a called a law in the same sense as Moore's law. It's an observation of a pattern, but biologists did not hold it as an absolute.

Re:Laws of probability

[hal9000]

... if mutations are truly random, isn't it necessary that they at least have the possibility to recreate a lost pathway, no matter how complex?

Yes, you're right. Here's an excerpt from Richard Dawkins' The Blind Watchmaker (via Daniel Dennett's Darwin's Dangerous Idea).

"'Dollo's Law' states that evolution is irreversible... [But] There is no reason why general trends in evolution shouldn't be reversed. If there is a trend towards large antlers for a while in evolution, there can easily be a subsequent trend towards smaller antlers again. Dollo's Law is really just a statement about the statistical improbability of following exactly the same evolutionary trajectory twice (or indeed any particular trajectory), in either direction. A single mutational step can easily be reversed. But for larger numbers of mutational steps... the mathematical space of all possible trajectories is so vast that the chance of two trajectories ever arriving at the same point becomes vanishingly small... There is nothing mysterious or mystical about Dollo's Law, nor is it something that we go out and 'test' in nature. It follows simply from the evolutionary laws of probability."

Re:Laws of probability

[orangesquid]

In the scientific method (AFAIK), anything that seems to have no evidence against it becomes a law after a while. It does not have to be proven rigorously; that is reserved for the worlds of mathematicians and Congress.

Evolution is difficult to study scientifically because large parts of it are partly based on speculation, rather than observation. Humans can not completely know the past before they existed, but can only guess at one of a set of implied possibilities based on evidence discovered; humans can not also experiment with the past, and since we can not experiment and we are not omniscient, we have to make guesses.

I think it would have been better termed Dollo's corollary (or is that too strong of a word? It doesn't necessarily follow directly, but Occam's Razor would probably lead to it) to evolution theory, or something.

Re:Laws of probability

[hal9000]

Oops. That should end "elementary laws of probability".

Re:Laws of probability

[barawn]

A "law" in science is more of an empirical observation - a guideline or principle. Kindof like Moore's Law. In general relativity, there's the "Law of Cosmic Censorship" which states that you can't have a singularity without an event horizon cloaking it. A much better mathematical term for what some scientists tend to use "law" for is "conjecture" or "principle".

Is it poor wording? Yah, but using "law" to describe a proven theory is falling by the wayside, since very little is truly provable, so "law" is almost getting a comic connotation.

Newton's third law is even pretty much a "conjecture", since we know the strong form of it isn't true in all cases, and while the weak is holding extremely well, it's entirely possible it may not be completely true.

Re:Laws of probability

[exp(pi*sqrt(163))]

Dollo's Law is a bit silly. It's like saying that there are no triangles in architecture where one of the angles is 57.138 degrees. It's probably true. Go out and find a triangle and measure its angles with enough accuracy and you'll probably not find one that has an angle of 57.138 degrees to three decimal places. Occasionally you will find such a triangle. You can just put those down as a rare exception to the law that doesn't fully invalidate it. This is obviously a pretty silly law. So is Dollo's, for similar reasons.

In case you don't quite get the analogy: at any moment in time there are multiple directions a population may take. Just as there are many angles besides 57.138 there are many directions for the population. In almost all cases it won't go back the way it came. But it might. Just as you might find a 57.138 degree angle.

Much simpler theory

[PhilHibbs]

Big creatures don't evolve much.

To adapt to a repidly-changing environment, you need a rapid turnover of new generations. Whales won't evolve their legs back again, they don't have the time to do it. Some other, smaller sea-creature will take up that niche. Maybe it'll then evolve to be really big.

Two stories about the evolution of flight in a row? Who'd'a thought it?

That is logical

[Ayende Rahien]

Living being have quite a lot of unused historical matter in their DNA.
The information isn't lost, it's merely isn't used, so if there is a need, it can be evoked quite easily, instead of having to discover it again.

Think of it as #ifdef for the genome.

Re:That is logical

[Catskul]

I absolutely agree. Anyone with college level biology(hs even) knows that traits can exist without being expressed, and know that there is more genetic information than is used in most organisms. It astounds me the articles that show up with fairly obvious observations being presented as the edge of science. I sincerely hope that it's just the article author that is exaggerating the situation rather than the scientists actually being shocked at this "new" information.

Re:That is logical

[Orne]

I totally agree... Mother Nature is a sloppy programmer..

I look at it like evolution spends a lot of time adding minor "features" to the program (or "bugs" like cancers which kill it off)... over time, some of those features aren't needed anymore, so the main function just doesn't branch out to that subroutine (protein) anymore, but it's still there. Which I guess is a metaphor for these "knock-out" genes, it's not that they destroyed the code, they suppressed the ability for the DNA to make that chemical...

Chromasomes, nature's DLLs... what a scary thought. ... Interchangeable at compile time, like forked code tinkered by thousands of programmers...

Just look at the GOP!

[Archeopteryx]

George W. Bush looks like he is about to start dragging HIS knuckles any time now.

What knuckles?

[Pflipp]

I want a tail.

De-evolve?

[Madcapjack]

It doesn't surprise me that wings couldappear and disappear. It would be surprising, i suppose, if you looked at biological evolution purely at the phenotypic level, but I don't. When something disappears, phenotypically, that doesn't mean that all of the coding for the phenotypic feature has also disappeared. Likely, it is just the bit of genetic code that kicks the process of growing wings off.

btw phenotypic thinking, i believe, is partially behind this misguided notion of missing-links.

*heh*

[oPless]

So what's next for some humans: a happy return to dragging their knuckles?

Well you yanks (mostly) voted him in!!!

Re:That is (Not) logical

[dracocat]

The information isn't lost, it's merely isn't used

Because the information is not used, it is not preserved. Remember natural selection helps keep the DNA in tact by only selecting those with the correct traits to survive.

For example, somebody may have a mutation to be born without a heart... Well, obviously they won't pass that along.

Without natural selection being involved, all of this unused DNA is useless, because it has probably all mutated by now, since it is not an active part of us.

In the case of the stick-fly, which is what this article is about, the DNA for the wings were somehow tied to the DNA of the feet. So that while the creatures were not flying, and didn't have wings, the DNA stayed in tact because the feet were required for survival.

So, unless the unused DNA that you are talking about is tied to another vital part of DNA that we DO use, then it has already worthlessly mutated.