Why Evolution is True is a blog written by Jerry Coyne, centered on evolution and biology but also dealing with diverse topics like politics, culture, and cats.
In Death Valley, this little guy wandered into our campsite. We fed him lettuce, which he ate with some reluctance. That wasn’t a surprise given that these birds (related to cuckoos) are largely carnivorous.
Fig. 1. The roadrunner, Geococcyx californianus.
Which of course brings this to mind:
by Matthew Cobb
Jerry suggested I post the following piece as a signing-off for my current stint as co-guest blogger.
The British media has started to fill its pages and programmes with retrospective pieces on the last decade – the noughties, as media types (but nobody else) calls them. For example, The Guardian carried this set of articles this weekend. Amongst the predictably true stuff about Google, iPods and 9/11, and the parochial British obsession with z-list celebrities, there was a brief piece about the key scientific discoveries of the noughties. So this was my question to Jerry:
What were the three most important biological discoveries of the noughties?
My list would be: Homo floresiensis (aka The Hobbit), the Human Genome (even though that’s not really a discovery, but an inevitable application of a technique) and, in an area I’m particularly familiar with, the discovery and continual re-discovery of insect olfactory receptors.
In 2000, three groups finally described insect olfactory receptors. The vertebrate equivalents had been isolated in 1991 by Linda Buck and Richard Axel, who went on to win the Nobel Prize in 2004. The gap in time was surprising, and was initially put down to the fact that, even in closely related species, olfactory receptors evolve extremely quickly, so looking for genetic sequences in insect genomes that were similar to vertebrate olfactory receptors was a tricky business.
But it soon turned out that things were even more complicated. In 2006, Richard Benton, a post-doctoral researcher in Leslie Vosshall’s lab in Rockefeller, showed that in fact insect olfactory receptors are completely different from their vertebrate equivalents. They are literally upside down – the bits that people thought were outside the cell, interacting with smells, turned out to be inside, connected to the machinery that makes the neuron fire.
Furthermore, Vosshall’s group showed that these receptors only worked if they had a co-factor, which is incredibly highly conserved in insect species. You can take the gene from a moth and stick it in a mutant fly, and the fly will smell again, even though lepidoptera and diptera are separated by about 200 million years of evolution.
Not content with making one stunning discovery, Benton and Vosshall made another at the beginning of the year. Shortly before leaving Rockefeller to set up a new group in Lausanne, Switzerland, Benton discovered a completely new class of olfactory receptor in insects, which works in a completely different way from previously-identified insect receptors and has a completely separate evolution.
In unpublished work his lab presented last week at a meeting I attended in Switzerland, he shows that this class of receptor is common to all studied protostomes (essentially the invertebrates, minus the sea urchins and some worms), but is absent from all deuterostomes (all other animals). You can track the path of evolution by the way that animals smell the outside world, and these ways are turning out to be incredibly rich and complex.
Benton himself is not only a very pleasant and incredibly modest young man (with not much to be modest about!), he is someone who having made some fundamental discoveries in cutting edge molecular neurobiology, recognises the fundamental importance of putting those findings into an evolutionary and ecological context. As Theodosius Dobzhansky put it, “Nothing in biology makes sense except in the light of evolution”.
You can read more about Benton’s work in this prize-winning essay, recently published in Science, in an open access section.
So – what would the readers of this blog (and Jerry) think were the three most important findings in biology in the noughties?
I’m back after ten fantastic days in Guatemala. What this means is that you’re going to be forced to look at my holiday snaps, beginning with Death Valley, continuing with the Atheist Jamboree, and then through Guatemala. Here’s a taste of each.
Fig. 1. On Artist’s Drive, Death Valley
Fg. 2. Dan Dennett introduces the idea of a “deepity”, Atheist Alliance International meeting, Burbank
Fig. 3. The Mayan city of Tikal, Peten, Guatemala. Atop Temple 2, with Temple 1 in background.
And yes, there are Guatemalan felids for Caturdays, too. But now I must rest.
Kudos to Matthew Cobb and Greg Mayer for their many nice posts in my absence.
h/t: Otter for Figures 1 and 2.
by Greg Mayer
As a herpetologist with a cat, I’m always interested in feline-reptilian interactions, and here’s a South African tortoise that either doesn’t like cats, or likes them so much that it gets close enough to annoy them and drive them away. Note that the orange tabby, at least, appears to regard its interactions with the tortoise as playful, much as Peyton regards her interactions with me (in the second video), thus demonstrating, once again, the rudimentary moral sentiments of cats. (Try to ignore the dreadful soundtrack.)
This clip from South African TV provides the context of the clip.
The original video by Salvelio Meyer, sans soundtrack, has had embedding disabled, but you can see it at Youtube, by clicking through the image below.
by Greg Mayer
WEIT readers know that cats are a frequent subject of posts here, and that the origin of the moral sentiment is another, although not quite as frequent, subject. The two topics have occasionally joined hands, mostly in the person (?feline) of my cat Peyton (see here and here). Well, it turns out dogs can have a moral sense too. PZ Myers has a wonderful video of a dog in Chile going out into a busy highway to rescue another dog which has been hit by a car.
Actually, despite our well-known ailurophilia (digression: OED take note– you don’t have this word yet!) here at WEIT, we’ve long known that dogs have rudimentary moral sentiments, and Darwin included observations of his dogs (the second of which was named Bob) in his writings on the subject (see here, especially chap. 3, and here both links are to The Complete Works of Charles Darwin Online). A sample (Descent, vol. 1, p. 77):
I have myself seen a dog, who never passed a great friend of his, a cat which lay sick in a basket, with-out giving her a few licks with his tongue, the surest sign of kind feeling in a dog.
Here’s a review on the subject Matthew did a couple of years ago, entitled “Are mammals moral?”, for the Times (the Times, not the New York Times).
by Matthew Cobb
Here I am preparing tomorrow’s lecture on Cnidaria (pronounced with a silent C) – jellyfish – when I bumped into this video. These are dolphins off the coast of Wales playing in front of a boat, the way they do, in that irritatingly cheerful dolphin way. Then, about 20 seconds into the video, they start using their tails to flip hapless jellyfish floating near the surface, as though they were playing football. I could have saved this for my next Z-letter, but given I decided to show it in tomorrow’s lecture to lighten things up, I thought I’d share it here too. What can you say? The people on the boat think it’s a hoot, and so too, I suspect, do the dolphins…
NB The video has no sound, unfortunately. The BBC site has the video, with the following text: “The bottlenose dolphins were spotted tossing the jellyfish off Tremadog Bay. Jonathan Easter, one of the team said the “incredible images…present more questions than answers!” Footage courtesy of Countryside Council for Wales, Sea Watch Foundation and Marine Awareness North Wales.”
by Greg Mayer
Although the mammals and reptiles most people know are quite distinct– mammals are hairy, warm-blooded, live-bearers, that suckle their young, while reptiles are scaly, cold-blooded, egg-layers– a wider knowledge of the modern forms reveals that the differences are less absolute. There are many live-bearing reptiles, for example, and platypuses and echidnas lay eggs and are nipple-less. And it has long been known that mammals are descended from a particular group of fossil reptiles: both the great British anatomist Richard Owen and the American paleontologist and zoologist Edward Drinker Cope noted this in the 1800s (Cope doing so in a paper with the wonderful title “The theromorphous Reptilia”, “theromorphous” meaning, roughly, “beast-shaped”).
Because the vertebrate fossil record consists mainly of bones, paleontologists need an osteological distinction between mammals and reptiles, and the definition of mammals is that our jaw joint is between the squamosal bone of the skull and the dentary bone of the lower jaw, while in reptiles the joint is between the quadrate and the articular.
The stages in the picture above were about all that were known to Cope and Owen, but they could still see the connection between the groups. (The lower picture is of a pelycosaur, an early type of synapsid reptile, the synapsids being the group of reptiles from which mammals eventually evolved; Dimetrodon was a pelycosaur). Cope’s identification of early synapsids as the ancestors of mammals could be considered a prediction that intermediate forms would be found (I leave out Owen, because his views on evolution were equivocal). Later work has abundantly confirmed this, and the reptile-mammal transition is now probably the best documented of all higher level transitions in the vertebrates. A classic paper by A.W. ‘Fuzz’ Crompton and Farish Jenkins, teachers of mine from grad school, summarized the first 100 years of work on the subject.
Here’s a diagram of one of the intermediate forms. Note that it has a double jaw joint, and the bones in the lower jaw have become much smaller. If you look above to the mammal, you will see that these bones have become even smaller still, and detached from the lower jaw.
What has happened is that two bones of the lower jaw (the angular and the articular), and the quadrate of the upper jaw, of reptiles have become (some of) the ear bones of mammals– the tympanic, malleus, and incus, respectively (mammals have another ear bone, the stapes, which is the only ear bone in reptiles). This reduction in size and detachment from the jaw occurred in many gradual steps over many millions of years, all documented in the fossil record. Clifford Cuffey has a nice set of figures of some of these, and Karen Peterson of the University of Washington has posted class notes with some very nice figures. What makes this even neater is that the jaws themselves are derivatives of the anteriormost parts of the branchial (gill) arch skeleton, a subject I’ve mentioned before, and thus we can trace the history of these bones from the branchial apparatus to the ear by way of the mouth.
Just as Matthew was inspired to post about sponges after lecturing about them to one of his classes, I bring up the ear bones because I was lecturing to my vertebrate zoology class about the branchial skeleton and its derivatives this past Tuesday. It was also the very day that the New York Times had an article by Natalie Angier on the evolution of the mammalian ear bones inspired by a recent paper in Science (subscription required for full article) by Qiang Ji and collaborators. They describe the jaw of an early Cretaceous mammal that had a persistent reptile-like connection of the ear bones to the jaw. The authors propose, quite reasonably, that this is a paedomorphic condition, that is, that it is the retention into the adult of an embryonic condition: mammalian embryos pass through a stage in which their jaw/ear bones resemble those of reptiles.
The working out of the history of these bones is one of the great triumphs of vertebrate comparative anatomy. Neil Shubin (sorry Jerry!) summarizes the highlights nicely in chap. 10 of Your Inner Fish.
by Greg Mayer
The Smithsonian‘s National Museum of Natural History (known to biologists as the USNM) has announced that its new Hall of Human Origins, first announced in 2006 and originally slated to open this year,will open in March of next year. Normally this would be unadulterated good news; WEIT readers will recall the ‘thumbs up’ I gave the USNM’s exhibits in August. But a New York Times article [update 20.iii.2010: link now dead] says that
The museum also is establishing an advisory group called the Broader Social Impacts Committee to foster discussion on how scientific and religious perspectives on human origins can be compatible.
This is a cause of concern. Scientific institutions should not have an official theology. This sure sounds like they want to endorse Catholicism (at least of the John Paul II kind) or mainline Protestantism or some other religion that doesn’t object to science (much). I don’t see any problem in having it pointed out that, “Look, there’s a scientist who’s religious” (e.g. Ken Miller). [Added later: or pointing out, “Look, there’s a religious leader who accepts evolution” (e.g. John Paul II).] But to foster the claim they are “compatible” beyond that simple empirical point is not a scientific endeavor.
Curator Rick Potts is a little more reassuring as quoted in the Times, stressing the evidence of human evolution, saying that the exhibit will be a
place to look at the fossil evidence, to explore the fossil evidence and the archaeological evidence that informs about human evolution.