If you are a keen rodent enthusiast, rats are likely to pique your curiosity, as they are quite unusual creatures that have often been maligned as dirty and disease-riddled – but in fact, they are very clean, highly intelligent, and extremely good pets. Many people are fascinated by these creatures and how they have evolved; they are dexterous and nimble, and watching them solve puzzles or climb around through your home is always an interesting experience.
If you have ever watched your rat picking things up, you may have wondered “do rats have thumbs?” Certainly, they can grip their food with ease, and they climb well and never seem to struggle when it comes to grabbing and holding items – but are their tiny hands like ours and do they have opposable thumbs? Opposable thumbs are massively important when it comes to gripping and manipulating objects, and it seems like rats should have evolved this extra digit at some point.
An opposable thumb is a digit that is angled differently from the rest of the digits on the hand, and this makes it significantly easier to pick items up and hold them, because they are being gripped from more than one direction. In general, this evolutionary feature is associated with primates, which needed to grip branches well, and it is a crucial aspect of humanity’s success.
Do Rats Have Thumbs?
No, rats do not have thumbs, or at least not thumbs that look similar to a human’s thumbs. However, they do have small nubs on their feet where a thumb would otherwise be, and this aids them somewhat when it comes to gripping food and manipulating it into the right position. It also makes it easier for the rat to climb and cling onto sloped surfaces.
If you hold a rat and gently inspect one of its front paws, you will see that it has four long fingers that are all aligned with each other, as on a human’s hand, and then one small nub on the side of its paw where a human’s thumb would be. This is tiny, almost unnoticeable unless you are looking for it, but it does help the rat use its paws properly.
Whether this should count as a rat having a thumb is up for debate. Some primates have extremely small nubs instead of thumbs, and yet we would still say that they had thumbs (spider monkeys are one example; a long thumb would get in the way as they swung through the branches). However, the nubs on rats barely constitute a digit, and a rat doesn’t have much power in its grip; it could not cling to something in the same way that a human could, and rats cannot tear at their food or pull pieces apart without using their teeth.
How Come Rats’ Front Paw Stumps Never Evolved Into Thumbs?
It’s hard to say why these little stumps have never evolved into thumbs throughout the rat’s evolutionary history, but in general, this feature is mostly associated with animals that spend vast amounts of their time in the trees and need a really good grip to minimize the risk of falling. Creatures such as koalas and opossums have developed opposable thumbs, as have the primate family, and these all depend upon being in trees for the vast majority of their lives. Rats, however, spend a lot of time on the ground and burrowing, and although they do climb, they don’t need to maximize this skill the way other animals do.
Furthermore, although opposable thumbs do offer many advantages, they also come with disadvantages, and many of these would be a significant hindrance in the rat’s common environment – for example, opposable thumbs tend to be weaker and more vulnerable to breakage, especially when running. Rats run on all fours, so if their front paws had evolved into thumbs, they would be at risk of their thumbs getting damaged (which may be why humans never evolved opposable thumbs on their feet). The rat’s little paw nubs, however, are small enough to minimize this danger.
Opposable thumbs might also be a disadvantage when digging, which rats spend a lot of time doing. In order to develop them, rats with longer thumb joints would have to have had a greater chance of survival and breeding than other rats, and this is clearly not the case.
Why Do Rats’ Rear Paws Have More Digits Than Their Front Paws?
You may have noticed that your rat only has four digits on its front paws, and five on the back, which seems odd given that most animals have the same number on all feet/hands. However, this may be a result of the thumb nub that rats have; it’s possible that this was the fifth digit and it has evolved slowly to become more opposable (improving the rat’s grip) but significantly shorter (to reduce the risk of damage when the rat runs or digs).
Rats cannot then grow an additional digit on their hands; they only have a certain number to work with (barring mutations) and therefore they only have four noticeable fingers because the fifth has become a short thumb. They can then use the muscles in their palms to grip things.
There could be other explanations for the uneven number of digits on your rat’s feet, such as the fifth digit being a nuisance or getting in the way, but this is the most likely one – since the fifth digit is still there in some form. Technically, the rat does not have fewer digits on its front paws; it’s just that one has become very small.
So, there’s no simple answer to the question “do rats have thumbs?” because they have a digit that serves as a sort of thumb, but this is very small and underdeveloped, and does not look much like a true thumb. Rats cannot use it in the same way as a human can use their opposable thumbs, and it is quite limited in terms of grip and manipulation. However, it does still allow some of the advantages of true opposable thumbs, and it certainly is something like a human’s thumb.