Rule of thumb for people hungry for bamboo and larvae

We sat gazing into the fading light.

Suddenly, there it was: this strangest and ugliest of the Madagascar lemurs, its big ears twitching and its round eyes bulging as it made its way along a branch. We were thrilled.

We also saw what makes the Ai-Ai really unique – the long finger on its front paw. It uses it for “tap forging”: tapping on tree branches and trunks, listening for echoes.

This indicates a hollow chamber inside, possibly containing the larvae. If the aye-aye hears the movement, it will poke a hole in the bark, insert one of those long fingers, and take the larvae out for dinner.

The ai-aye’s sharp hearing, that long finger and this use of echo-location to find food are all remarkable and acutely distinct evolutionary adaptations. But that’s not all there is to note about it.

There are many endemic lemur species in Madagascar—ring-tailed, grey-headed, sifaka, indri, etc. They are attractive animals for a variety of reasons.

The most interesting thing for me is that their thumbs are like ours. Namely, they are “opposites”, which allows animals to take things in the same way that we do. The creatures look like cats or dogs – check out their noses, the shape and size of their bodies – but their hands are like ours. It’s shocking when you meet him for the first time.

The exception though, is Aye-Aye. It has no thumb like its lemur cousins. In fact, expert use of that long middle finger doesn’t seem to even require a thumb.

But in 2017, a team of biologists from North Carolina State University (NCSU) realized that the aye-ace might have what might be called a pseudo-thumb like growth on the wrist.

Given the remarkable middle finger and all that had to do with it, no one had paid any serious attention to this growth. Maybe it’s just a bone deformity, I don’t know. Still, the lesson of evolution is certainly that every body trait you can imagine has a cause.

In their paper, A Primate with a Panda Thumb: The Anatomy of the Pseudothumb of Daubentonia Madagascariensis (https://bit.ly/3QinH4n, 21 October 2019), the biologists write that the pseudothumb of the ai-aye consists of three muscles. , These have the ability to “collectively enable abduction, adduction and opposition”—three motions that your own thumbs can do.

But of course, it’s “probable”, they mean, because it’s still a rudimentary digit. So, why is this at all? NCSU scientists suggest a hitherto “unfamiliar” role: it “compensates for over-specialization” [the aye-aye’s] fingers for non-grabbing tasks.”

This refers specifically to “tap forging” by the middle finger. The finger is so exquisitely crafted to tap and then dig up the larvae that it’s almost useless for anything, such as moving. If Aye-Aye Gus and I saw it used to hold the branches as the spiny finger moves, it is easily broken by the weight of the animal.

The theory, then, is that this pseudo-organ evolved to compensate for that fragility. Interestingly, we have here one trait that has evolved because another trait has evolved for a very specific task. But then the Aye-Aye is a very special creature.

But wait—this isn’t the only creature that has a pseudothumb. The paper above is titled giveaway- the famous crazy giant panda also has one.

Here’s an animal that belongs to the order Carnivora, which means you’d expect it to eat meat. But it eats the bamboo with the weight of the stick. If you’ve ever chewed sugar cane, you’ll know what it contains. You hold the cane in your fist – but if you didn’t have a thumb, it would be nearly impossible for you to hold it. Like most other mammals, pandas actually have only five fingers, none of which are opposable thumbs. Still it is able to hold the bamboo like you and I will hold the cane. 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 gnawing on bamboo in which it is clear how important the pseudo-limb is.

And yet, it raises an obvious question. Why didn’t this enlarged bone develop into the actual thumb, the sixth finger of the panda’s hand?

It’s worth asking because of an archaeological find, a team of scientists in China just reported (Oldest giant panda suggests false thumb movement and conflicting demands for food, https://go.nature.com /3OKFik2, 30 June 2022). Excavating at a site called Shuitangba in southern China, they found the fossilized remains of a panda that lived several million years ago in the Miocene epoch.

This ancient panda ancestor already had a wrist stubble like the modern panda, as well as the adversary.

So really, why didn’t that ancestral bone spur develop into a fully functional, fully opposable thumb?

The hypothesis here reminds, if on the contrary, of A-Ace. It is the movement of the lemur that prompted the development of its pseudo-limb. But it’s the panda’s speed that stunted the development of his elusive thumb. Pandas move around, on their soles and palms (“plantigrade pose”). Hence, they step on that elusive thumb forever. If it gets any bigger, it will be crushed because the panda was lumbar along.

That’s why I hope to someday sit down with both Panda and Aye-Aye. They can see me twirling my opposing thumbs.

Dilip D’Souza, once a computer scientist, now lives in Mumbai and writes for his dinner. His Twitter handle is @DeathEndsFun.

first article