Peter and Rosemary Grant, known to all evolutionists as simply “The Grants,” have just come out with a new (April, 2014) book on their long-term field work, 40 Years of Evolution: Darwin’s Finches on Daphne Island (marginally cheaper at Amazon). I haven’t yet read it, but I know the work well, for the Grants do much of their research in my own field, speciation.
And, nine days ago, Jon Weiner wrote about the Grants’ book and work in a New York Times article called ‘In Darwin’s footsteps.” Weiner, as you may know, wrote a book about the Grants’ work two decades ago, The Beak of the Finch, which won a Pulitzer Prize for nonfiction. His new article updates the old one, although by necessity it leaves out many of the gazillion findings the Grants have made since then.
The Grants’ research program on the Galapagos began in the mid 1970s; for the first ten years it was carried out by students and postdocs (like my colleague Trevor Price; see below), and the Grants began working on the island themselves around 1985.
Nearly all of the Grants’ work, by the way, takes place on a tiny and godawfully desolate volcanic cone in the Galápagos: the island of Daphne Major, which has only a few trees (genus Bursera) and no fresh water (all supplies, including water for long field seasons, is brought in by boat and carried up the hill). It’s about 5 km², and so is tiny. But it has finches:
One of the Grants’ findings is singled out by Weiner: a possible new “hybrid species” formed after hybridization between existing species twenty-odd years ago. It was itself founded by a probable hybrid male formed by interbreeding between two of the archipelago’s 14 finch species, and the male then mated with a member of one of its parental species (a “backcross”). That created (over a decade later) a population that interbreeds only among itself, and, if you employ the Biological Species Concept, its reproductive isolation from other species and interbreeding among itself means that we have seen, in just a few years, the creation of a new species. Biologists find such speciation exciting because the possibility of new species forming by hybridization between others is not only fast, but something we can study, as the Grants have in real time. It belies the creationists’ claim that we’ve never seen new species form. (I deal with that issue in both WEIT and my book Speciation with Allen Orr, showing that we already know of several “polyploid” plant species that have formed in historical times.)
The interesting thing about this hybrid finch “species” is that the isolating barrier between it and other species is based almost entirely on song. The males inherit their song culturally, by hearing and imitating their father, and females mate with the song they hear when they’re nestings. That means that since the original hybrid male (a descendant of the populations’s hybrid founder,”Big Bird”) had an unusual song, his descendants would sing only that song (if male) and mate only with males singing that song (if female). The lineage would be interbreeding but isolated from others. And while there are some genetic differences between the new hybrid species and any other finch species, the isolating barrier itself could be based on culture, not genes.
My own view is that there are some good cases of hybrid species, but that the phenomenon is probably not ubiquitous. The Grants are wary of calling this new population a “species,” though for the time being it’s certainly acting like one. My colleague Trevor Price at Chicago, who got his Ph.D. working with the Grants on Daphne, isn’t inclined to call it a species because, he feels, it may eventually fuse with another species via hybridization. (He points out that two well-demarcated species on Daphne, the cactus finch and the medium ground finch, are hybridizing fairly extensively, and my one day fuse.)
But I consider species concepts to operate in the here and now, not prospectively. Who knows whether this new isolated lineage will persist? Whether it does is a matter of waiting. Do we decide, for instance, that we’ll call it a new species only if it is still distinct in 2090? Nevertheless, my own view, like Trevor’s, is that the existence of this “species” is precarious. But so long as it lasts as a population for at least a while, and doesn’t mate with other species, we can provisionally say we’ve seen The Origin of A Species.
I got to know Peter and Rosemary when I did part of a sabbatical in Princeton, and I called them “The World’s Nicest Scientists.” I meant that, because they’re simply wonderful and generous folks. And they’re tenacious: I, for one, couldn’t maroon myself on a desolate island for several months every year to study the birds onsite. I love my Chinese food and urban attractions too much. But the Grants have persisted for four decades. They’re both 77, and, as Weiner says, they know they can’t keep it up forever. But it’s still the longest-running and most fruitful field work on evolutionary genetics and ecology that I know of, and the Grants deserve the many honors they’ve accrued. Here they are on Daphne, working away: