Biology Forums - Study Force

From a purely theoretical, or fantasy, perspective. Could humans have developed with our thumbs on the bottom, and how would we be different?

I am curious, firstly if it is possible, seccondly how things would be different, if humans thumbs were on the bottom edge rather than the top edge of our hands.

From my thinking about it. The thumb would end up being thicker as it would be used as the grasping support rather than the other 4 fingers we currently use(for example holding a cell phone, spear, book).

I would also think that the other 4 fingers would have more dexterity and possibly be longer.

I don't know if any other anatomy would have to be different, such as elbow direction or location of shoulder joint.

Any and all opinions welcome!

You mean like this?

Features evolve only if they're beneficial to our survival. You must ask yourself, how would this feature increase our survival and reproductive capabilities? The current configuration is referred to as being "opposable" because the thumb can be moved around to touch the other fingers, which gives people the ability to grasp things. Most primates and some other animals have opposable thumbs to swing, climb, in our case, producing weapons to hunt or start fires in nature.

@bio_man, nice drawing!

What I mean is that it would still be an opposable thumb, just on the exact opposite side of our hands.

We share a common ancestor with all primates, including baboons, orangutans, and chimps, but at some point we diverged. Our hand is most similar to that of a chimp, as you can see below. Notice how almost all primates have this configuration, where the thumb point towards each other from top view and it remains short. However, in pronograde monkeys such as baboons, an adaptation to a terrestrial lifestyle has led to reduced digit length and thus hand proportions similar to those of humans.

(https://i.pinimg.com/originals/ee/18/88/ee188893bee1f7ff1181fd0d25f4bb2e.jpg)

According to Wikipedia, a primitive autonomization of the first carpometacarpal joint (CMC) may have occurred in dinosaurs, while a real differentiation appeared in primitive primates approximately 70 million years ago.

(http://www.liberaldictionary.com/wp-content/uploads/2019/01/carpometacarpal-joint-5480.jpg)

I can only speculate that it's positioned where it currently is due to natural selection. I know that's fluffy answer, but I'm really not trying to avoid it. It couldn't be in the opposite side because our little fingers (pinky) do a better job being thin and small as they are than would a thumb :-\

In the case of people with Triphalangeal thumbs, they have an extra bone in their thumb, so it sort of appears like that you mentioned:

(https://3.bp.blogspot.com/-u1p_CpB_MLY/WyT_BMrDqRI/AAAAAAAACxE/q8yv9RfycuYvAfF7s7Zt9W7hZ8qg7DAowCLcBGAs/s1600/2018-06-12%2B08.22.25.jpg)

(https://ars.els-cdn.com/content/image/1-s2.0-S0266768104002049-gr1.jpg)

Hence, it is possible, but uncommon -- 1:25,000 births.

I don't see that being beneficial to our survival any other way.

Being on the inside ensures better balance for primates that use their hands to walk and a better grip.

I would think that it would be a better grip the other way. Especially for spears, and general tool wielding.

Probably true, since we only started making tools after we had evolved. @duddy I don't think we coevolved with the need to make tools for our survival.

If things had gone the other, surely lots would be different today. From playing playstation to typing messages on our funny, it'd be interesting