So what makes 6,000 years so extraordinarily fast? Bacteria can split into two species in much less time, but they swap packages of genes even outside of their species. For more complex, multicellular life, scientists often adhere to the biological definition of a species—two groups become so genetically distinct they cannot interbreed. Sometimes different species mate and produce young, but those hybrid offspring are usually sterile, as in the mule's case.
Some of the most studied speciation rates are among the more than 600 species of cichlid fish in Africa's Lake Victoria and neighboring lakes, which evolved sometime in the last 250,000 years (pdf). Even small color changes are enough to create red and blue fish that become different species.*
Speciation time depends on generation length and selection pressures, including limited habitat and food or threats such as disease and predation. Still, the two sea star species would win in an evolutionary race, at least among animals. Coyne gives a few examples: fruit flies in the wild can diverge in 200,000 to three million years and some North American song birds may have split some 170,000 years ago.
Plants are a different case, and claim spots at both ends of the spectrum. A doubling of their genome can overcome the typical genetic dead-end of hybrids, as in the recent case of a Scottish flower, and new species could theoretically arise in three generations, Coyne says. Yet populations of Liriodendron tulipifera, the tulip tree, remain one species despite being isolated for millions of years.
As surprising as the sea stars may be, evolutionary theory does predict such rapid speciation, Coyne says. The two sister stars offer a prime opportunity to study the rate of genetic change, not only because they share a recent common ancestor, but also because the changes are so dramatic.
*Editor's note (8/10/12): To increase its clarity, this paragraph has been edited since posting.
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7 Comments
Add CommentRe: "Finding out exactly which changes...mutation rates...led to this speciation event is tricky."
Reply | Report Abuse | Link to thisMy understanding is that the vast majority of mutations is neutral at best, deleterious at worst. What is an example of a beneficial mutation which could have been responsible for the "speciation" event herein described?
It would be good having a freshwater starfish, it will help eliminating or reducing the population of tiger mussels and other pests. Anybody in the genetic engineering field considering working in this line?
Reply | Report Abuse | Link to thisI quote a portion of this article:
Reply | Report Abuse | Link to this"The researchers haven't yet pinpointed which genes are most important for gender determination and reproduction in starfish, which is relatively unstudied, Grosberg says. The changes that distinguish C. pentagona from C. hystera may be just a handful of genes—or thousands."
If the above is true, that the researchers don't even know which genes are involved in gender determination or reproduction, how is anyone expected to believe they have any notion at all about how long ago these species have diverged or, even if they ever did.
I get very tired of the outrageously extrapolated claims many so called scientists make.
quizzical,
Reply | Report Abuse | Link to thisthe article responds to your point. All you need to do is read:
The scientists "...analyzed genes in the two species' nuclear and mitochondrial DNA to discover how recently the sea stars diverged."
This method is based on a statistical principle called sampling. It has a sound mathematical foundation, and unless someone has evidence for the opposite, I would generally consider people from the genetic discipline quite capable of doing the maths behind that.
To understand which genes encode the sexual functions and behavior is a task that cannot be done just by sampling; you would need a 100% inspection in order to get a complete sequence of the genetic code.
So, sampling is a way to answer one question - evolutionary relationship - but not enough to answer a second one, encoding genes.
These people are probably right, and you are definitively wrong.
Thanks for the clarification.
Reply | Report Abuse | Link to thisQuizzical, it is important to the ability of society to enact policy based on scientific understanding, that you take a lesson from this. When you say that you are "very tired of the outrageously extrapolated claims many so called scientists make", you are yourself making an 'outrageously extrapolated claim'. This really doesn't happen in the world of peer-reviewed journals. There are other problems with such controls, but the peer-review system tends to be marvelously self-correcting for "outrageous claims".
Reply | Report Abuse | Link to thisWe live in a world in which a democracy needs to drive changes in policy in the face of inevitable and extreme modifications of our biosphere which are still only visible through the lens of scientific scrutiny. But that democracy is largely controlled by people who believe that scientists engage in, at best wild claims, and at worst active conspiracies to fabricate evidence and crises.
It is gravely important that you understand that, while human and given to the same failings as all humans, scientists in their professional lives perform their jobs in a structure which engages the critical and competitive spirits of other scientists to ensure that their evidence is supported and their conclusions are reasonable.
The fact that this is so is proven by the advanced technological world around us that that very structure has made possible.
dbasener,
Reply | Report Abuse | Link to thisTo your first paragraph:
I am glad to hear that it rarely happens in the world of peer reviewed journals. I trust that Al Gore’s error riddled movie was not part of that process. The trouble is that when too many peers believe the same notion, who is left to challenge any nonsense?
A case in point – evolution itself. Many evolutionists insist that evolution is not a random process. But, no matter how many subsequent parts of the theory are non-random, if the whole house of cards rests solely on random variations, which it must if one is to believe the completely naturalistic concept, then the whole thing must be a random process.
And, of course – abiogenesis. One major reason for Mars exploration is to find the building blocks of life. Seems like everyone forgets that Life is NOT based on a correct recipe alone. But just as importantly, it is based on specific coded instructions that direct the use of the correct recipe.
There is NO scientific knowledge of any information ever being self-generating. Is there?
To your second paragraph:
Those folks you refer to are usually at the mercy of the media who are possibly the real source of wild claims. What are folks to think? Most folks are not privy to “peer reviewed journals.” Even this SciAm article’s title makes unsupported statements of fact which, to the author’s credit, are more correctly described in the text using terms such as “they estimate”, but their 6000 year estimate is plus 333% and minus 17% - a very strange and lopsided range.
To your third paragraph:
Don’t worry, I understand that. It is just that articles such as this one are VERY misleading in their thrust.
To your fourth paragraph:
Close investigation of Biology, Chemistry and Physics has indeed yielded a wonderful array of useful technologies. However, I would like to hear of one item whose development depended critically on speculations of origins. Origins cannot be studied experimentally with the scientific method. No one has millions of years to apply to the effort. Therefore all such speculations remain just that, and should never be sold as fact. I am only asking for truth.