Slashdot Mirror
How Predictable Is Evolution?
sciencehabit (1205606) writes "If the clock rewound, would organisms evolve the same way they did before? Humble stick insects may hold the answer to that long-running question in biology. Through studies of these bugs, whose bodies match the leaves the insects live on, researchers have found that although groups of the bug have evolved similar appearances, they achieved that mostly via different changes in their DNA. 'I think it says that repeatability of evolution is very low,' says Andrew Hendry, an evolutionary biologist at McGill University in Montreal, Canada, who was not involved with the work."
Just look at how many times Eyes have independently evolved, yet they all have the same basic components.
We put water, methane, CO2, etc. in a closed system, ran some simulated "lightning" through, and got amino acids and what not forming. Various experiments show similar (even more prominently supporting) results: Nature and physics shapes the beings that exist within it.
There are plenty of other examples of evolution coming to similar results from different ends -- Just look at the shapes of sharks and whales. Not going to further dignify this anti-intellectual ignorant rubbish. Use a damn search engine, that's what we built the web for.
Convergent evolution suggests it is somewhat predictable, unrelated species having evolved similar solutions to similar problems. If a solution is clearly better nature will tend to go there given sufficient time and experimentation (mutation).
The fact that a trait may be expressed by different DNA sequences doesn't really seem to undermine this. The DNA sequences are implementation details. Evolution is about solutions and environments not DNA sequences.
The degree of molecular similarity in the DNA changes to achieve a particular result will depend strongly on the type of change one is looking at.
For the case of toxin-resistance, which is much closer to the molecular level, the odds of similar changes to the DNA are much higher than for complex morphological changes.
Molecular changes like toxin-resistance are more likely to involve a single gene that codes for a single enzyme, changing the enzyme so that the toxin is no longer metabolized in a harmful way. There are going to be a very limited number of ways to do this because it's pretty close to a one-gene/one-enzyme mapping in many cases.
Morphological changes, on the other hand, involve a whole network of genes that are turned on over the course of development, and the network can be altered in many different ways to get to the same result. Think about it like a road network where you're used to taking a particular route to get from A to B. If a bridge goes out on your your usual route, you may choose different alternatives depending on time of day, the kind of vehicle you drive, etc. Networks create choices.
Even then it will depend on the kind of morphological change we are talking about.
For example, there is a lizard in Mexico, which was studied in the '80's or '90s. There were several related species living inland, and a couple of isolated species on the coast near the Yucatan peninsula. Both the coastal species had an extra cervical (neck) vertebra, and it had been assumed on the basis of this similar morphology that their evolutionary history had been a general migration to the coast, an adaptation to coastal environments that involved having a longer neck, followed by a general die-back that resulted in the two existing but separate populations.
It turns out based on their genes the two coastal species hadn't had a common ancestor for millions or tens of millions of years, and the adaptation to coastal living had happened independently but fairly recently. In this case, because certain aspects of body plan are controlled by a highly conserved and relatively simple set of genes, the additional vertebra were the result of similar sets of genetic changes.
Things like body width, which is what TFA is talking about, are a lot more complicated in their regulation, so more likely to be achieved via different genetic changes that have the same morphological outcome.
I'm going to throw in a shameless plug here because it seems relevant to the topic at hand. I've just published a hard SF novel that's premised on a what-if about the role of mathematics and law-like descriptions in evolution. If you're interested in that sort of thing you should check it out: http://www.amazon.com/Darwins-...
Blasphemy is a human right. Blasphemophobia kills.
If I'm reading this wrong, and I hope I am, please let me know.
...researchers have found that although groups of the bug have evolved similar appearances, they achieved that mostly via different changes in their DNA. 'I think it says that repeatability of evolution is very low...
I read this as "Stick bugs have reached similar appearances through different means thus the same change probably won't make the same result".
Is this equivalent to "People can change their appearance to include a hole in the abdomen through different means (bullets and knives). Thus shooting or stabbing people are unlikely to produce holes in people"?
It may make it more difficult to guess which DNA change caused them to look like that (without an actual DNA test), but it in no way implies that those DNA changes won't necessarily cause them to look like that.
Looking at cows, dolphins and horses genetic proximity shows unexpected results, as cows and horses are not the closer in the trio, despite their similar features.
That suggests environment drives evolution in a predictable way, while the genetic evolution is not. This is the really amazing point: evolution find similar solutions to similar problems, but it does so through different ways.
Refer to Stephen Jay Gould and his "Wonderful Life" http://en.wikipedia.org/wiki/B... also. Gould mentions that there were a range of various paleobiological doohickeys bopping around at the same time, and we come from one group that happened to swim better, or whatever. Next time round, we'll have five eyes.
Well, I'm not explaining it right, but that's why there's books...
"The greatest lesson in life is to know that even fools are right sometimes" - Winston Churchill
Yes you are reading that wrong. What they are saying is that since you can end up with similar looking creatures that took different DNA routes to get there, it's only the results that matter and not the DNA framework.
If you can end up with the same body style with different DNA then if you rewind the clock and started over there would be no reason to believe that you would end up with the same creatures we have today.
What can be asserted without evidence, can be dismissed without evidence.
Can we get a Star Trek like movie but instead of meeting human looking weirdos in outer space, let's meet species that look really weird, yet make friends with us and we commnunicate. Like Octopuses, and Snake-people, bug-looking-people, birds with intellect, Koala bear looking chess players, etc.
We know precious little about how evolution proceeded here, and we know nothing at all about how it might have proceeded elsewhere.
We can guess that it would be carbon based, because carbon has four covalent bonds and would have been formed sooner than silicon (with 4 bonds, but lower energies) would have. Beyond that, we'd need a few dozen D20 dice to calculate the odds.
But any real scientist knows that at some point, we have to admit WE DON'T KNOW how it might turn out. Wild-assed guesses aren't science, even if some people who claim to be scientists are sometimes wild-assed guessers.
not imaginative enough. Life in outer space would be less similar to us than bacteria on Earth is (so bird-like and octupus like is too "tellocentric"). Having said that, certain body plans are likely to reoccur like light sensors (eyes have developed several times independently on Earth) likely close to the proccesing unit ("brain", could also be distributed like in an octopus) and feeding organs.
Solaris (book more than movies) is IMHO just about the only popular SF that's pointed out plainly that aliens are likely to be truly alien. Most of the book is about how a vast amount of work in a century since contact did little other than reflect the views the researchers had before they even came in contact with the alien/s. Even with godlike powers the alien/s couldn't get a message through from the other direction either.
Greg Egan had another approach where a chain of cloned and increasingly altered intelligences could form a bridge to communicate with aliens.
There's a great book by the artist Wayne D. Barlowe, called "Expedition". it shows the life forms of a fictional planet called Darwin 4 . With dense atmosphere and low gravity, Everything evolves big, and almost nothing has anything like eyes (sonar is both popular and often very advanced). Without giving too much away for those who still haven't run across this, there are several common body plans that tend to run through whole phyla, and which don't occur on Earth, but make really good sense on Darwin 4. The underlying science is generally sound - I base this on the way various people who have read it point to this or that creature as less probable than the others, but seem to pick out different ones. This book has become my standard for SF aliens.
Who is John Cabal?
Actually no. Because both drivers had to use their respective route again if they drive again from Town 1 to Town 2. After some generations you would have two different tribes of drivers, one that drives along the grocery store and the kindergarden, the other one via the gas station and the library. And if the video store closes, some drivers of the first tribe cease to drive at all because it doesn't make sense to them anymore while the new hardware store causes other drivers of the first tribe to morph into a subtribe that drives to the hardware store instead.
I can see this point several times over. For instance, if complex animals developed on land before sea, perhaps we would have a eye better suited for terrestrial conditions instead of one that has to work in suspended aqueous solution. A terrestrial eye would benefit a great many species. Instead we managed to get this one trait passed on from generation to generation only modified to work in the existing environment. The downside of complex evolution is once you have committed to a certain path, getting rid of a trait can be next to impossible unless that trait no longer serves a purpose. Even then, we have moles with eyes that haven't seen light for generations.
Place something witty here
Sector General: The TV Series! I'd watch the shit out of that show. There are few concepts that allow for multiple truly alien species all living and working together that don't involve exploration and warfare; a massive hospital space station built for the express purpose of intercultural contact is a brilliant way to do it.
Hmm, sonar actually seems like a poor choice for one important reason: it's *active* - meaning that in order to be able to "see" something you basically have to scream at it, which would make both hunting and fleeing predators far more difficult since stealth is not an option. Meanwhile the very first creature to develop even crude imaging eyes would have a massive advantage. Also, it's considerably more complicated, so unlikely to prove a viable means of detection until the organism has independently developed both some sort of "ears" and a way to make loud sounds, whereas so long as there is light in the environment "eyes" start becoming useful as soon as an organism develops light-detecting compounds, and the benefit improves smoothly as directionality and imaging evolve.
Basically on Earth very few creatures use sonar, and typically they are apex predators (very few things hunt whales or flying bats). I suspect that's for a very good reason.
--- Most topics have many sides worth arguing, allow me to take one opposite you.