by Thomas Fernandes

A rodent with orange teeth and a paddle tail comes across a river. He tries to build a lodge but the stream is too low so he grunts, “Dam!”.
While the pun captures the beaver in miniature, the real story lies in the web of relationships that shapes it and the ecosystem in return. To see how deeply a species is shaped by these relationships, it helps to look first at its body.
This 20 kg semi-aquatic mammal is an extraordinary swimmer. It uses its tail as a rudder and webbed hind feet to glide efficiently through water. It can hold its breath for up to fifteen minutes thanks to a suite of cardiovascular adjustments known as the diving reflex. This reflex slows the heart and redirects blood flow to vital organs, a trait shared with seals and penguins.
Their fur is equally adapted: a very soft underlayer traps air and provides insulation with an incredibly high hair density (ten times the density of human hair), while a covering layer of longer guard hairs repels water, a property further enhanced by oil secretions that act like wax. Even their eyes are specialized for underwater vision, equipped with a nictitating membrane (a third transparent eyelid) that functions as natural goggles underwater.
By observing their bodies, it would be tempting to think nutria are close relatives. After all, they share water-repellent fur, webbed feet and even a diving reflex.

But looks can be deceiving: beavers and nutria split from a common ancestor 50–60 million years ago, long before humans and chimps parted ways just 7 million years ago. This is a case of convergent evolution, showing that similar environmental pressures can produce similar forms even in lineages with very different histories. Yet such adaptations are always built on top of existing genetic heritage. To understand what truly set beavers apart, we need to turn away from look-alikes and toward their real cousins in the desert. The closest living relatives of beavers are North American desert-dwelling burrowers. Examples include kangaroo mice and pocket mice. Despite their vastly different appearances, observing their behavior reveals deep evolutionary continuity. Read more »




Today an electrician came to visit. He was tall and broad-shouldered and had arms like sausage links that were fairly covered in tattoos. One of the tattoos was a date: January something-or-other. I tried to read it as he walked through my front door, but he looked me in the eyes and so I glanced away quickly without having absorbed any of the details. He had come to inspect my attic wiring, for which he had to get on his hands and knees and crawl around the attic floorboards. It was a short but dirty job. When he came downstairs his palms were blackened and so he asked if he could wash up somewhere. I pointed him to my kitchen sink and to a small bar of soap on one side of it. While he was washing his hands (very thoroughly, I noted), he turned to me and starting cheerfully recounting how important it was to him to be clean. He had a pink, friendly face, sort of like a big baby. He had shaved blond hair that had grown out ever so slightly and a twinge of orange in his beard stubble. I told him I was accustomed to dirt, having two sons and a male dog, although upon saying that I realized I wasn’t sure whether my dog’s sex was much of a factor in how dirty or clean he tended to be. The electrician nodded when I spoke but seemed eager to get back to his own story. He went on to tell me that he had a child but that he was no longer together with the mother. It’s not like me to have a one-night stand though, he said, it’s not a hygienic thing to do. And anyway, he went on, I could never have stayed with her—she was a slob, an unbel-IEV-able slob. She couldn’t focus, couldn’t pay attention to me or anyone else, and certainly not her surroundings. Keep your eye on the ball, I told her, but she didn’t know what I meant. Believe me, he said, that girl and all her stuff was all over the place.

The Hanle Dark Sky Reserve is a spectacular spot in Ladakh, in the north of India. It’s surrounded by snow-capped mountains, and at 14000 feet, it’s well above the treeline. So the mountains and the surroundings are utterly barren. Yet that barrenness seems only to enhance the beauty of the Reserve.
A bit of information is common knowledge among a group of people if all parties know it, know that the others know it, know that the others know they know it, and so on. It is much more than “mutual knowledge,” which requires only that the parties know a particular bit of information, not that they be aware of others’ knowledge of it. This distinction between mutual and common knowledge has a long philosophical history and has long been well-understood by gossips and inside traders. In modern times the notion of common knowledge has been formalized by David Lewis, Robert Aumann, and others in various ways and its relevance to everyday life has been explored, most recently by Steven Pinker in his book When Everyone Knows That Everyone Knows.
Sughra Raza. Departure. December 2024.



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