Hey, isn’t this the time of year you should be traveling to exotic places, diving and snorkeling in tropical oceans, and of course, sending your underwater photos to me to inspire acute envy? That’s what Philip Qua did, and here are some cephalopods spotted in the Caribbean reefs off Cozumel.
I keep saying this to everyone: if you want to understand the origin of novel morphological features in multicellular organisms, you have to look at their development. “Everything is the way it is because of how it got that way,” as D’Arcy Thompson said, so comprehending the ontogeny of form is absolutely critical to understanding what processes were sculpted by evolution. Now here’s a lovely piece of work that uses snake embryology to come to some interesting conclusions about how venomous fangs evolved.
Basal snakes, animals like boas, lack venom and specialized fangs altogether; they have relatively simple rows of small sharp teeth. Elapid snakes, like cobras and mambas and coral snakes, are at the other extreme, with prominent fangs at the front of their jaws that act like injection needles to deliver poisons. Then there are the Viperidae, rattlesnakes and pit vipers and copperheads, that also have front fangs, but phylogenetically belong to a distinct lineage from the elapids. And finally there are other snakes like the grass snake that have enlarged fangs at the back of their jaws. It’s a bit confusing: did all of these lineages independently evolve fangs and venom glands, or are there common underpinnings to all of these arrangements?
I was asked to contribute to Forbes Magazine package on commuting — never mind that I live across the street from my job, and “commuting” has become a trivial, alien concept — so I had to talk about animals that commute.
It seems to be an evolving tradition around here to put descriptions of our medical adventures online. Janet contributes with a an account of her recent mammogram. I was disappointed — there are no pictures.
Hey! I’m scheduled to have a colonoscopy late next month! Shall I…?
Life has two contradictory properties that any theory explaining its origin must encompass: similarities everywhere, and differences separating species. So far, the only theory that covers both beautifully and explains how one is the consequence of the other is evolution. Common descent unites all life on earth, while evolution itself is about constant change; similarities are rooted in our shared ancestry, while differences arise as lineages diverge.
Now here’s a new example of both phenomena: the development of segmentation in snakes. We humans have 33 vertebrae, zebrafish have 30-33, chickens have 55, mice have 65, and snakes have up to 300 — there’s about a ten-fold range right there. There are big obvious morphological and functional differences, too: snakes are sinuous slitherers notable for their flexibility, fish use their spines as springs for side-to-side motion, chickens fuse the skeleton into a bony box, and humans are upright bipeds with backaches. Yet underlying all that diversity is a common thread, that segmented vertebral column.
The similarities are a result of common descent. The differences, it turns out, arise from subtle changes in developmental timing.
This is a long streaming video, so you might want to save it for something to watch over lunch. Mark Norman takes a giant squid apart at the Melbourne Museum.
