(Image courtesy of Wired.com)
How many times have you heard someone ask the question: “Have scientists ever actually observed the formation of a new species?” Our standard answer is that speciation is an event that occurs over thousands of years, one would not expect to be able to observe it. However, a fascinating paper in the journal Proceedings of the National Academy of Sciences (PNAS) appeared this past Monday written by Peter and Rosemary Grant — a husband-and-wife research team who have spent the last 36 years studying Darwin finches on the Galapogos Islands. Never in the history of biology has a single set of scientists so thoroughly studied a group of organisms in their natural environment, following them through the span of multiple decades. The work, outlined in a book we highly recommend, The Beak of the Finch
by Jonathan Weiner, has been a masterpiece–science at its very finest. So thorough is their analysis that in this PNAS article they are able to actually demonstrate the key events in the formation of a new species as it occurred before their very eyes. A single species has diverged to become, in essence, two species–they are no longer inter-mating. One would have to follow the organisms for a longer time to see if they become firmly established as two distinct species, but the important point is that as we approach the 150th anniversary of the publication of Darwin’s Origin of Species next Tuesday, careful analysis has showed that it is actually possible to observe the key events of speciation. And the events associated with it happened in less than one human lifespan!
The findings describe the mini-evolutionary saga that took place on their island of Daphne Major in the Galapagos chain. The Darwin finches of the Galapagos islands (technically from a family called “tanagers”) first provided Darwin with a clear picture of evolutionary divergence, as birds from each island have adapted unique traits to meet the unique conditions of their respective islands. The new species observed by the Grants can be traced back to a medium ground finch (Geospiza fortis) that arrived from a neighboring island in 1981. The bird was “unusually large, especially in beak width and sang an unusual song” (The Grants tape recorded the immigrants song!)
Despite being a newcomer, this ground finch was able to successfully mate with a female from the local island. Together, they produced five sons. However, because young Darwin finches learn their songs from their father, the offspring learned a new variation of the local bird call, a product of the song being mimicked through the voice of their foreign father, similar to a human singing a song in a language they do not know.
Despite this slightly different tune and their unusual size (which they also inherited from their father), this new generation was still able to find mates. However, the Grants theorized that within a few generations, this new lineage would become reproductively isolated from the local population. Sure enough, after four generations when a drought killed off all but a brother and sister of the new lineage, the remaining siblings mated. Their children began to do the same. After three generations of reproductive isolation, the Grants have declared that the birds are now in the “secondary stages” of species formation.
The ultimate future of the newly reproductively isolated group remains to be seen. Will they be out-competed for resources or will genetic problems from the variations in the patriarch and matriarch of the lineage become magnified over time? Perhaps, even, members of this new group will return to the island of their forefather and interbreed with them, leading to even more genetic diversity.
At the very least, the saga of these finches shows that while rarely observed, speciation can occur quickly given the proper circumstances.
posted November 18, 2009 at 1:45 pm
My understanding of evolution is that it is change of a species by random genetic mutations. Selection of the fittest promotes advantageous mutations, etc. This study does not seem to me (and I am not well trained) to be evolution, but rather a study in breeding. Perhaps you can comment on this to help me (and others without a thorough biological background) better understand its significance.
posted November 18, 2009 at 2:51 pm
Hi Brandon,
The generation of mutations produces new variants. So on a long term basis mutation is very important. However, speciation itself occurs as two populations become reproductively isolated from one another. In this case, new mutations probably played no role in the reproductive isolation. What happened is that a male arrived from another island and it sang a slightly different song than other members of the species on the island. Despite that difference he was able to mate when he arrived in 1981. He then taught his song to his sons, who also mated with members of the surrounding population. They sang the same song as their dad. However, as the population grew, females descended from the original male, when given a choice, preferred to mate with males who sang their grandfather’s (and then great-grandfather’s) song.
Please keep in mind this is only the very first step…it would take hundreds of years probably longer for the two isolated species to become very different from each other. New mutations would likely play a significant role in generating more and more differences between the species. However at the start, reproductive isolation of two very similar populations is what gets things moving.
Great question!
Best,
Darrel
posted November 18, 2009 at 4:15 pm
Hm. My “standard answer” is to refer the person to TalkOrigins’ Observed Instances of Speciation.
posted November 19, 2009 at 1:06 pm
The example of speciation I would use would be the common cordgrass (spartina anglica), which is now an invasive species colonising the tidal mudflats around the world… It came from a hybrid around 1890 between an introduced american an a european cordgrass species, and is fertile but doesn’t intercross with the both parent species…
posted November 19, 2009 at 4:17 pm
Um, just an observation, but, er, all of those finches are still birds. Just, birds.
posted November 20, 2009 at 6:39 am
Um, just an observation, but, er, all of those finches are still birds. Just, birds. – Mere_Christian
Just an observation, and a remarkably stupid one. Evolution of major taxonomic groups takes place over millions of years, and is in many cases (evolution of mammals from reptiles, of tetrapods from fish, of whales from their land-living ancestors) very well documented in the fossil record.
posted November 20, 2009 at 4:32 pm
Background: Random house defines speciation as “the formation of new species as a result of geographic, physiological, anatomical, or behavioral factors that prevent previously interbreeding populations from breeding with each other.” Note that the key part of this definition is that interbreeding is no longer possible.
If we peel away all the breathlessness, what has this article really told us? We start out with a finch, which mates with another finch, producing finch offspring, which in turn mate with each other producing an isolated group of finches, who according to the author, have the following potential: “Perhaps, even, members of this new group will return to the island of their forefather and INTERBREED WITH THEM, leading to even more genetic diversity.” (my emphasis)
I’m going to go way out on a limb and make a scientific prediction: when this happens, the offspring will be… are you ready…
Finches.
posted November 21, 2009 at 6:00 am
Brain,
You’re an idiot. Read my previous comment.
posted November 22, 2009 at 12:15 pm
Hey, its Helping People Learn to Read and used
check out these grammar software
Regards
posted November 22, 2009 at 9:34 pm
Hi Knockgoats,
Yours is an impressive line of argument. I’ve always preferred bonehead to idiot, but if you like that one better, OK.
Since you’re such an expert, may a simple idiot ask a question? Given your reference to millions of years, I take it you also disagree with the claim made by the article that a speciation event occurred “before their very eyes?” Unless of course the Grants are quite a bit older than they look….
thanks in advance,
Brian
posted November 25, 2009 at 5:58 am
Brian,
You truly are a bonehead, if that’s the term you prefer. Speciation is not the same as the evolution of major taxonomic groups. As a matter of fact, your first comment was factually incorrect, because “Darwin’s finches” are not, in fact, finches, but tanagers. Each single speciation event will involve a relatively small change, but over long periods, these small changes add up to larger ones – so one group of species gives rise to others (successively larger groups of species are classified as a genus, family, order, class or phylum). So, Darwin’s finches, found nowhere but the Galapagos, are more similar to each other than to any other birds, but the next most similar are other tanagers living in mainland South America. Tanagers as a whole are more similar to each other than to anything else, but still quite similar to finches. Tanagers, finches and a lot of other birds are all classified as the order of passerines, because of similarities they all share. Passerines are grouped with other organisms that have feathers in the class of birds, and so on. Get the idea?
If you find it hard to get your head round the idea of successive small changes adding up to a large one, where do you think you came from, Brian? Did the stork bring you? Or did you start as a single cell, when your Daddy put a seed in you Mommy and it merged with her egg? (Maybe we should “teach the controversy” about these two theories, eh Brian?) But in any case, you started out quite small, and not able to walk, talk or control your bowel movements – that much, the two theories agree on. And look at you now! Quite grown up – except for the brain, which unfortunately seems to have had its growth severely restricted by all that creationist bone. Never mind, Brian, if you can stop clinging to your ignorance, there’s still hope for you. Why not give it a try?
posted December 1, 2009 at 2:57 pm
Hi Knockgoats,
Sorry for being away for so long; life gets busy.
One more time:
1. Speciation is, according to Random House, “the formation of new species as a result of factors that PREVENT previously interbreeding populations from breeding with each other.” Note the key is not that they do not, but that they cannot mate.
2. The finches/tanagers discussed in the article can still interbreed with each other.
3. Therefore, the claim that speciation has occurred–breathlessly, before the very eyes of the researchers–is, well… specious.
That’s the point, and it’s really a pretty simple one. Of course, you can restate the broad outlines of neodarwinian theory or of child development; you can try to score points by making trivial distinctions that none of the referenced books and articles make; you can even continue to make disparaging personal comments about me if that’ll make you feel better about your ideology. But the logic is really pretty straightforward.
-Brian