# eli5/Why are our fingers all slightly different lengths?

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eli5/Why are our fingers all slightly different lengths?

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Make your hand in to a fist and turn it over and look at your finger tips – they are all in a row now! Our finger tips are different lengths when extended so when we close them (either to grasp something or to clench our fist) they fit together well.

There is no evolutionary advantage to having identically-sized digits; mammals with irregularly sized digits didn’t die off early prior to reproducing so it was never an important factor. The digits we have are “good enough” from an evolutionary perspective.

It’s hard to prove, but I think there are two things at play. First: The index finger has to be a certain length to work well with the thumb. Second: When you do a pull-up your arms slightly rotate, so the ring finger and pinkie have to be shorter than the middle finger to line up. Most of the load will be on the middle finger and ring finger. If they were the same length only the pinkie would make contact.

Millions of years age when the first fish walked out of the sea and onto land, its fins/bones had already formed into different lengths. The bones did this because of natural selection (what works best ends up being passed to offspring).

We are the decedents of that fish.

So when we eat using our hands, the tips of the fingers are at the same length and can pick up food properly.

Hold up a bowl, or clench your fists… you’ll notice your fingertips align. So I believe it’s to do with better strength when gripping items. Tree-climbing animals have different-length digits too. It greatly benefitted humans because we started using tools.

All sounds very plausible and I just want to add my thoughts.

I also think it’s because most (… all?) organic systems follow the fibonacci numbers / sequence (1,1,2,3,5,8,13,…) / golden ratio in their proportions when growing, like the order of leaves, branches of trees, snail houses etc and kind of grow in a circular way to fill the space as well as possible coming from one source, like a puddle.

The thumb and general finger size and position enable us to hold something, so that’s functional, but the position of all finger tips together is like an invisible circle, when outstretched.

Additionally a small detail: the length of the ring and index finger in comparison is also influenced by hormones we got as embryos. In the end it’s still circular.