My dog would surely love to be able to open the back door but she has one big problem; she doesn’t have opposable thumbs. Oh, she can run faster, bark louder and has a better olfactory sense than I do but that pesky lack of thumbs prevents her from doing a lot of things she really wants to. In fact most of the animal kingdom, outside of primates, would love to have that thumb which can touch the other four fingers. Provided that you have four fingers of course. Even then, most primates who do have opposable thumbs, find them more suitable for climbing, than for using tools or texting.
In this select group we have, Humans, old world Monkeys, Apes, and some Lemurs (and their Asian cousins the Loris) all have opposable thumbs. A few of them even use rudimentary tools but making those tools as opposed to finding them is the big difference. Along with the grip.
Every being in the family of those with Opposable thumbs have the power grip (Honey, I can’t open this Jar) but only Humans and a few higher apes have the precision grip (hand me a scalpel). In a power grip the thumb is used as a counter balance to the fingers and the palm is part of the operation. In a precision grip the thumb works in concert with only a few fingers to perform more delicate operations and all this without having any muscles in said thumb.
Now obviously if you’re using your hands to propel yourself forward, there’s very little chance you will develop an opposable thumb. So, until we stood up, there was no way we could start the long march to thumbhood. It also helps to stay out of trees where many of our primate relatives like to hang out. And again the more opposable, the better the grip. Superior tools, more precise use of those tools (think the way you wrote letters in kindergarten versus as an adult) and of course better control of that club, sword, or even gun, gives you an edge over the other guy. This gives your children good opposable thumb genes, and provides them with a much better chance to not only live but procreate. Therefore passing those first-rate thumbs a little farther down the line. Kind of a form of genetic hitchhiking.
Julius Caesar knew well the importance of this digit, and would remove the thumb from captured enemy warriors, so they couldn’t employ a weapon against the Roman Army ever again. I would imagine this was indeed quite effective and more than likely a deterrent to others. The fact that we give things the thumbs up or down also comes to us from the Romans, through the gesture known as Pollice Verso. Now this Latin phrase translates as turned thumb and gives no true indication of which direction (or if indeed it was instead hidden) meant life or death.
The French artist Gerome’s painting Pollice Verso is where the thumbs down really got going and subsequently the use of thumbs up to show approval. This was greatly facilitated by American WWII pilots who used the upward thumb to mean everything is good, let’s go. A medieval gesture indicating approval of a deal may also have something to do with our use of thumbs up but no one really knows. Regardless of where it came from it’s a universally accepted gesture in our world, and not the only one. The OK hand signal (thumb touching one finger) is also widespread, with the clenched fist (I am ticked) being not far behind.
And remember it’s one thing to smash something with a rock repeatedly, in order to open it up and another altogether to paint like Vermeer. The next time you write your name, turn on a stove or even open a door be thankful for opposable thumbs. And if you don’t mind please let the dog out.