Their that's actually called the Palmyra's longest.

And around 15% of people actually do not have this muscle in either one or both of their arms.

Let's see I do have it in that one as well, and that's because it's a vestigial muscle, which means that an ancestor to humans likely used it to climb in trees or walk on their forearms.

But modern humans don't really have a use for it.

And so some people just don't have it.

And to be a vestigial muscle, it's got to be something that doesn't cause a disadvantage or a consequence.

So people who don't have this don't have a lower grip strength than people who do.

In fact, it's often one of the first muscles they remove when they're wanting to do reconstructive surgery on another part of the body and that's on evolution.