July 29 Ah, Madagascar. What a country. I loved my two months backpacking there: the people, the sights, the hard knocks ... and the lemurs. I've always wanted to return, but haven't managed it yet. One of these weeks, for sure.
But those lemurs. The oddest of them all is the aye-aye, and I feel lucky to have actually seen one. They are usually nocturnal and hard to spot, so I was lucky to see one just before dusk turned to night one day. And all these years later, I learn something about them that connects them to another fascinating animal, the panda. So that's what my column for Mint is about today. Read it, and let me know if it strikes a chord with you. Thumb rules for those who hunger for bamboo and larvae, https://www.livemint.com/opinion/online-views/thumb-rules-for-those-who-hunger-for-bamboo-and-larvae-11659028867048.html cheers, dilip PS: For more about the aye-aye, may aye recommend Gerald Durrell's delightful "The Aye-aye and I". For more about the panda ... well, I'm not sure I should recommend "Kung-Fu Panda". --- Thumb rules for those who hunger for bamboo and larvae Too many years ago, I went searching for the aye-aye. I was backpacking in Madagascar and had met a tall, rangy Dutchman called Guus. "We should try to see the aye-aye," he said once as we trudged through the forest on the Masoala Peninsula. From Maroantsetra the next evening, a little row boat took us downriver to a little island where a wiry young man pointed into the tree above us. We gazed up in the fading light. Suddenly, there it was: this oddest and ugliest of Madagascar's lemurs, its large ears moving and its round eyes bulging as it made its way along a branch. We were thrilled. We even saw what makes the aye-aye really unique - the long finger on its front paws. It uses that for "tap foraging": tapping on branches and trunks of trees, listening for echos. That indicates a hollow chamber inside, possibly containing larvae. If the aye-aye hears movement, it will gnaw a hole in the bark, insert one of those long fingers and yank out the larvae for dinner. The aye-aye's sharp hearing, that one long finger and this use of echo-location to find food are all remarkable and acutely specialized evolutionary adaptations. But that's not all that there is to note about it. Madagascar has several endemic lemur species - ring-tailed, gray-headed, sifaka, indri, etc. They are fascinating animals for different reasons. To me, the most fascinating is that their thumbs are like ours. That is, they are "opposable", which allows the animals to pick up things the same way we do. The creatures look like cats or dogs - check their noses, the shape and size of their bodies - but they have hands like ours. Which is rather startling when you first encounter them. The exception though, is the aye-aye. It doesn't have a thumb like its lemur cousins do. In fact, its expert use of that long middle finger seems to suggest it doesn't even need a thumb. But in 2017, a team of biologists from North Carolina State University (NCSU) realized that aye-ayes do have what might be called a pseudo-thumb, like a growth on the wrist. Given the remarkable middle finger, and everything aye-ayes do with it, nobody had paid any serious attention to this growth. Maybe it was just assumed to be a bone deformation, I don't know. Yet the lesson of evolution is, surely, that there's a reason for every body feature you might imagine. In their paper, "A primate with a Panda's thumb: The anatomy of the pseudothumb of Daubentonia madagascariensis" ( https://onlinelibrary.wiley.com/doi/10.1002/ajpa.23936, 21 October 2019), the biologists write that the aye-aye's pseudothumb has three muscles attached to it. These "collectively have the potential to enable abduction, adduction and opposition" - three motions your own thumb can perform. But of course, it's "potential" they mean, for this is still a rudimentary digit. So why is it there at all? The NCSU scientists suggest a so far "unrecognized" role: it "compensates for overspecialization of [the aye-aye's] fingers for non-gripping functions." This refers specifically to the "tap foraging" by the middle finger. The finger is so exquisitely crafted for tapping and then digging out larvae that it is useless for nearly anything else, like moving. If the aye-aye Guus and I saw used its spindly finger for gripping branches as it moved, it would easily break with the animal's weight. The theory, then, is that this pseudothumb evolved to compensate for that fragility. Intriguingly, we have here a feature that evolved because another feature evolved for a very specific function. But then the aye-aye is a very special creature. But wait - it isn't the only creature with a pseudothumb. The title of the paper above is a giveaway - the famously cuddly giant panda also has one. Here's an animal that is of the order "Carnivora", meaning you'd expect it to eat meat. But this one eats bamboo, by the stick-load. If you've ever chewed sugarcane, you have some idea of what this involves. You grip the cane in your fist - but if you had no thumb, you'd find it nearly impossible to hold it. Like most other mammals, the panda actually has only five fingers, none of which is an opposable thumb. Yet it is able to hold bamboo like you and I would hold sugarcane. How? It uses an enlarged bone in the wrist that acts like a sixth finger; in fact, like an opposable thumb. There are videos of pandas munching on bamboos in which it's obvious how vital the pseudothumb is. And yet that raises an obvious question. Why did this enlarged bone not evolve into an actual thumb, a sixth finger on the panda hand? This is worth asking because of an archaeological finding a team of scientists in China have just reported ("Earliest giant panda false thumb suggests conflicting demands for locomotion and feeding", https://www.nature.com/articles/s41598-022-13402-y, 30 Jun 2022). Digging at a site called Shuitangba in southern China, they found fossilized remains of a panda that lived in the Miocene Epoch, several million years ago. This ancient panda ancestor already had a wrist stub like modern pandas do, seemingly opposable as well. So indeed, why didn't that ancestral bone spur evolve into a fully functional, fully opposable thumb? The hypothesis here is reminiscent, if contrariwise, of aye-ayes. It's the lemur's motion that spurred the evolution of its pseudothumb. But it's the panda's motion that stymied the evolution of its pseudothumb. Pandas get about on all fours, on their soles and palms (in a "plantigrade posture"). So they are forever stepping on that pseudothumb. If it grew any larger, it would be crushed as the panda lumbered along. All this is why I hope to sit down someday with both a panda and an aye-aye. They can watch me twiddling my opposable thumbs. -- My book with Joy Ma: "The Deoliwallahs" Twitter: @DeathEndsFun Death Ends Fun: http://dcubed.blogspot.com -- You received this message because you are subscribed to the Google Groups "Dilip's essays" group. To unsubscribe from this group and stop receiving emails from it, send an email to dilips-essays+unsubscr...@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msgid/dilips-essays/CAEiMe8pBr0uckWX__%3DevTVEMnb80yMabvg3%2B2q4uEV8_ygxqRg%40mail.gmail.com.