What Makes Humans Unique?

There are many features of humans that differentiate us from all other species, but there is one that stands out to me as a key influence for many of the others and the main reason for our huge success as a species, and that is our practice of the Division of Labour, facilitated through trade¹. We are the only species where each individual specialises, and depends on the specialised skills and resources of other unrelated individuals for their survival².

In social insects, like ants and bees, there is specialisation into roles – some individuals become queens, the rest become workers, and among workers there can be those that specialise as builders and others as fighters. But there is a significant difference, which is that in social insects the division of labour does not cross the reproductive unit (and correspondingly can be genetically determined). In social insects it is only the queen that reproduces³, so a colony of social insects is much more like a single organism where the individual insect roles are like component organs⁴⁵, than a social species where individuals cooperate but also have their individual and independent interests. In humans, the division of labour can cross reproductive units, and even family and social groups.

Though in many other species there is cooperation across reproductive units within social groups, the difference there is that it is only ever of the ‘symmetrical’ kinds. This includes reciprocal cooperation, such as sharing, where both parties benefit from the insurance they get from the arrangement. It also includes teamwork, where all parties benefit because they are able to achieve things that weren’t possible to achieve individually. Reciprocal cooperation is driven by our instinct for empathy, where we understand others by relating them to ourselves, and our instinct for tit-for-tat, where we only cooperate with others who also cooperate. Teamwork is driven by our instinct for groupishness and an us-them mentality. These instincts are not unique to humans, and both these symmetrical kinds of cooperation can be found in many other species. The difference with the division of labour that humans are capable of is that the ‘labour’ is not just shared symmetrically among individuals, it is divided asymmetrically into separate roles that individuals specialise in.

In any other case where there is asymmetrical cooperation outside the reproductive unit, it is between species themselves. These are mutualistic symbioses such as the cooperation between bees and flowers or the cooperation between cleaner fish and their clients. The difference with the division of labour is of course that it is cooperation within a species (and correspondingly needn’t be genetically determined).

There are many new gains to be made from the asymmetrical kind of cooperation that happens with the division of labour, for a species which is sufficiently adaptable. The initial gain of a division of labour, which is what incentivises a trade in the first place, is that each party saves on the initial and ongoing overhead costs of the ‘product’ they do not produce. But what differentiates trade from any other form of cooperation with mutual benefit, is the cumulative nature of these gains. Firstly, when an individual specialises in one product instead of two, any improvements they can make to the efficiency of their trade will have twice the gains that it had before, and what’s more, unlike in a sharing relationship, the individual can keep all the gains to themselves, increasing their incentive to invest. Any time saved from improvements to the process can then be reinvested into further improvements, and so there is a compounding effect which means the gains accumulate over time. Secondly, there is nothing stopping two or more independent trades happening simultaneously and when that happens the gains from each trade are simply added together, so the more people there are to trade with each other the greater the potential gains from division of labour. (There isn’t a practical limit to how much this can scale either as trade doesn’t require personal relationships). These cumulative effects together mean that over time and with increasing sizes of societies, there can be huge gains in efficiencies from the division of labour. Modern society is the ultimate testament to this.

It is already well established in economics, this role that division of labour has played at the economic level in developing the wealth of nations, but perhaps it equally has played a role at the biological level in shaping some of our uniquely human traits. Indeed there is evidence of extensive trade networks as far back as 300,000 years ago, before homo sapiens started to evolve, so this is not impossible⁶. Not everything unique to humans can be explained by trade though. For a start, a minimum level of adaptability is needed just for there to be a benefit from the division of labour. Also I think a certain level of language would have been present before any trade, in line with the high levels of adaptability⁷. While these are unique to humans now, they may not have been unique among other species of the homo genus, that have until relatively recently co-existed with homo sapiens. Trade, however, could be unique to our species within the homo genus, and could be responsible for our relative success. Also it could be associated with many other uniquely human traits.

Firstly, trade requires a minimum precision of communication to be viable, enough to establish a primitive form of ‘contract’. This requires much more precision than in symmetric cooperation, because there is not a comparison of like with like, and so it is not possible to judge by eye or intuition whether an exchange is fair. (It’s not even theoretically possible to objectively agree an exchange rate, which we’ll come back to later!). Therefore as a minimum, a species needs to be able to count and communicate number. This may be the humble origins of abstract reasoning and generative language.

Secondly, division of labour through trade incentivises further improvements to our adaptability (which consists of learning and creativity)⁸. This is because, as already mentioned, when you specialise in a skill there is a greater payoff in investing in improving that skill, and unlike in teamwork or sharing, there is a separation of concerns meaning that any gains you make in improving the skill can be kept to yourself; this could be either improving the efficiency of the process in which case you save time, or improving the quality of the resulting product in which case you can get more in exchange. This may in turn strengthen selection pressures for communication, for the purpose of better transferring this increased knowledge from parent to child.

Thirdly, there is a lot that can be exploited for individual benefit in the negotiation of a trade itself. And that is because in a trade there is not a predetermined exchange rate, which is because a trade being mutually beneficial precisely depends on the relative value of the exchanged products being different for each party. As such there is always a range of exchange rates at which a trade is viable. If you can reason about how the other party values your product better than they can about how you value their product, you can win a higher proportion (up to the whole) of the profit from the trade. The profits from trade are sufficient that many people can specialise purely in this skill as middle men for trades, extracting a portion of each trade they facilitate. This is called arbitrage, and is the essence and origin of all financial work. Arbitrage is incentivised at the individual level and creates selection pressures for improvements to abstract reasoning, for example to enable calculations. It also incentivises new kinds of communication – exploratory communication to identify potential trades, and persuasive communication to sell things to other people by appealing to their own self interests⁹.

Other selection pressures that trade creates are indirect; many of our uniquely human behaviours can only evolve in the context of larger societies, and I think stable societies above a certain size threshold would not be possible without trade¹⁰. The scalability of trade is something that sets it apart from any other form of cooperation. In symmetric cooperation, like teamwork or sharing, the weaker parties benefit more than the stronger parties, which makes the selection pressure significantly weaker for non-kin relationships and therefore limits how far these cooperations naturally extend. To extend to non-kin relationships, symmetric cooperation requires significantly more trust which requires closer personal relationships, again limiting the size of networks; the cognitive limit to the number of people with whom one can maintain stable social relationships is known as Dunbar’s number¹¹ and is about 150. Trade, however, can be a stable arrangement between unrelated individuals who also do not know each other personally. I think it provides the original ‘glue’ for any ‘society’ larger than Dunbar’s number (or thereabouts). Trade is a natural bond because it ties the fate of the two parties together to an extent, and therefore is a natural basis for an alliance. For the first time ever, there is an incentive from the point of view of natural selection, for people to have a sense of groupishness with, and care to some extent about the welfare of, individuals they don’t know personally. There is also an increased need to be able to appreciate the existence of a system greater than oneself¹². This could have paved the way for Culture, Religion, Gods, Ethics and ultimately Law, Authorities and Politics.

It’s with the size of networks, that the division of labour has advantages that dwarf the costs. An individual human is very similar, and no more prepared for survival, than an individual chimpanzee. Even a small (isolated) group of humans has little advantage compared to a small group of chimpanzees. But in numbers of 150 or more, where relatively ’primitive’ forms of cooperation that rely on personal relationships break down, the advantages of trade come into their own, and over time the compounding effects have led to, at times exponential, progress that has put the human species into a league of its own.