the story of our hands can be traced back to when ancient creatures like tiic used their fins to crawl out of the sea some 375 million years ago ancient mammals modified those fins into Paws creatures like Hyrum had short fingers that all pointed in the same direction tipped with claws then a hand appeared that was very different and we can see it in a tree dwelling species called narus this ancient hand can tell us a lot about our hands today un meeting fossil hunter Jonathan block he has a pretty complete skeleton of nartis a primate that was first discovered in Wyoming territory in 1870 wow the real this is the this is the real deal that is absolutely Exquisite this is a 50 million year old primate skeleton it gives us a window straight into the world of what the earliest primates would have been doing how they would have been interacting with their environment like most modern monkeys neth Arcus was a climber adapted to life in the trees the evolution of this creature and others like it had a huge impact on one of the features that most defines us our [Music] hands thumb is Divergent that is it forms an angle with the index finger and so that shows you that it could bring its thumb into opposition with the rest of the digits nartis also has long fingers and nails instead of claws this is one of the first times in the fossil record that we see a hand that looks like our own the hand of a primate it's a turning point in the history of the human body an anatomical change that would eventually let us shape the world around us but why did primates evolve such a hand in the first place okay to find out I'm going to look for Clues where my ancient ancestors lived up in the [Music] trees thankfully I've got ropes okay ready got it natural woohoo a little naughty up here okay woohoo these creatures are so unbelievably agile all through here this is their home they are able to live on small branches big branches throughout the tree they can jump Branch to Branch you know when you're in the tree what you see is that the canopy is not one place there are lots of environments lots of niches up here and one special one is on the ends of the branch es because it's there where the flowers and the fruits and the insects are so the rewards are great to be out there we call it the fine Branch Niche and for the earliest primates being able to navigate the small branches there was vital and that gives us a clue as to why their hands were so different from what came before creatures with really short fingers and Claws they're really great at crawling these big thick branches but not so much when you get to the ends of the branches that's because this sort of hand can't grasp lengthening the fingers and better still adding a Divergent thumb means you can curl your fingers around even the thinnest branches grasp them tightly and remain stable we think that's why the hands and feet of early mammals changed what you end up with are primate hands well adapted to moving around the fine branches of trees just like these monkeys here embedded in our bodies is our distant past the hand I used to write with to type one the computer to throw baseball that hand has a long evolutionary history and one important point in that history was here in the trees on the fine branches that made a hand with longer fingers and the thumb [Laughter] [Music]