How Hand Dexterity leads to Human General Intelligence

Carlos E. Perez
Nov 28, 2018 · 7 min read
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Photo by Dominik Scythe on Unsplash

Isn’t it a curious coincidence that the words “point”, “probe”, “sift”, “pry”, “feel” and “tweak” are words that relate simultaneously to cognitive behavior and our hands?

Here I’m going to make the case that our hand dexterity is the driving force for our unique general intelligence. There are plenty of other animals that do have big brains and live their lives in a social context, two ingredients postulated to drive higher intelligence, yet have not evolved to the sophisticated intelligence found in humans. Elephants, whales, seals and primates all have sufficiently large brains and rich social structures, but what they all lack that humans do have is hand dexterity.

Whales and seals don’t have appendages that can hold anything. Elephants have trunks that are quite dextrous, but is probably equivalent in capability as two short fingers. Primates like Chimpanzees, Gorillas and Orangutans do have five fingers on their hands, however, they’ve evolved into a form that isn’t as comparably dextrous.

My argument goes as follows. Primitive humanoids had similar hands as we have today. These hands enabled the use and eventual the creation of tools. The creation of more advanced tools required learning a sequence of process steps. These steps required a lot of experimentation to discover. To preserve knowledge about tool making, humans that could teach their offspring how to perform a sequence of process steps had a survival advantage. This learning of encoding of sequences led to language primarily in the form of hand gestures. This eventually evolved into spoken language.

We can gain inspiration from Umberto Eco’s interpretation of Semiotics (the study of signs and their interpretation). Semiotics will classify signs as being indexes, icons and symbols. Indexes are causal signs that relate to an object, and icons represent signs that are similar to an object, these are the basic blocks of understanding in tool making. Symbols become useful for expressing advanced ideas that are required by tool making. Eco describes a typology for sign production:

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Which describes the work require to produce new expressions. In short, dexterous hands are needed to interact with objects in complex ways, experiment, and then invent new tools and followed by the communication of how to create these tools.

It turns out that human-like hands are more primitive than is commonly thought. Human-like hands can be dated back 6 million years. A very short time after the human-primate evolutionary split.

A primate’s hand gives them a forceful curling grip that a human cannot match. It’s a capability that’s useful for hanging and swing from trees. However primates do not have as much control at their fingertips. The human hand has an opposable thumb that allows for the thumb to be pressed with force against the fingers. In addition, the fingers of a human hand are much shorter than primates, allowing the thumb to reach the finger tips. The hands of primates had actually evolved further away from the original dexterity afforded by a primitive human-like hand. In short, primates have evolved away from the capability that could have led them to higher intelligence!

A key principle of evolution is that it is generated only from the adjacent possible. A species can evolve into an alternative path that closes them out from access to capabilities that could give rise to higher intelligence. Whales, dolphins and seals evolved flippers from their limbs and thus closing them out from the evolutionary branch afforded by hands with dexterity. In evolution, there are no rollbacks. Species can’t un-evolve functionality despite its detrimental utility.

Human sign language have a kind of expressiveness that can be absent in spoken language. Recent research by NYU linguist Philippe Schlenker reveals:

They are, in a sense, ‘super languages’ — and they have a unique contribution to make to our understanding of human meaning.”

Sign language makes visible logical structure that can be implicit in spoken language. Subjects can be identified by their position in space (example: left or right) and they can be referenced by a pointing index finger. In addition, iconic modulations, that is degrees of magnitude can be expressed more easily and can be done simultaneously with logical expressions.

The human infant is able to learn the skill of pointing in X months time. Understanding location, magnitude and identity are primitive cognitive capabilities that are now expressible via hand gestures. Sign language likely was a skill developed by humanoids prior to their vocal cords evolving to facilitate spoken language.

But what motivated the evolution of complex language? A new theory about the origins of language proposes that language arises from the adjacent possibility afforded by tool making. The dexterity afforded by human hands leads to the discovery of many skills required for making tools. The most effective tools required discovery of a step-by-step (i.e. sequential) methods. That is, certain steps must be performed prior to previous steps. Furthermore, this required some level of long range planning to ensure that parts are available when they are needed.

The primitive hominoid would therefore have in his memory the kinds of raw materials required for tools. In his daily explorations, if he encounters any of these raw materials or even perhaps even novel materials, then he would make the effort to collect these. Collecting stuff to build stuff isn’t a higher cognitive capability, birds, squirrels and beavers do this all the time. Thus, it’s not far fetched to think that primitive hominoids could learn to collect more kinds of raw materials for use in creating more kinds of tools.

The cognitive leap is that in learning the skills to craft together more complex tooling. Crafting sharper stones required for hunting requires a high level of repetition and skill. Oren Kolodny and Shimon Edelman, theorize that the emergence of language required the skill of performing sequential processes in the crafting of complex tools. The fact that human hands are involved in both tool crafting and in sign language leads to a natural coupling of these skills. Primates by contrast don’t have communication capabilities coupled with sequencing capabilities.

Kolodny and Edelman argue that the neural networks required for complex, hierarchical, sequence-dependent tool production were exapted by our brain’s communicative apparatus, which is why word order and sentence structure make such a difference to meaning.

The emergence of language is driven by the social pressures required for survival. This complex language skills originates from our tool crafting skills and is ultimately tied to the dexterity that we have with our hands. The neural circuitry that allows us to create things is the same as what allows us to communicate. Perhaps that is why many writers love a mechanical keyboard.

Now that we see the importance of dexterity with regards to general intelligence, what then can we make of the general intelligence of octopuses?

Further Reading

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