What makes humans special?


There is obviously something special about man, the most recent master of planet Earth. For starters, if we put our minds to it, we can dominate almost any other species out there. We know how to domesticate dogs and cattle, poison ants, trap lions, genetically engineer mice and make bacteria clean our sewage. Humans also collectively reshape entire ecosystems and have managed to colonize even space. Man dominates his environment in a way that no other animal can compete with. But do we actually know what gives us our competitive edge?

Our common sense tells us that the answer has something to do with our thinking capabilities. Humans just seem more clever than anything else you could possibly encounter in the woods or the fields. But there is a catch: we also tend to be quite self-absorbed and do not realize what other species are really capable of. Once one delves more deeply into the cognitive secrets of other animals, the list of specific thinking skills possessed only by man shrinks down very fast. Let us now step through some example skills, all of which have been suggested to be uniquely human, and see how much of us remains truly unique.

1. One thing we absolutely depend on is other people.

Humans are successful within a culture. Culture allows us to store and transmit collectively accumulated knowledge. A newborn is unlikely to reinvent himself all the way from the Stone Age to the Iron Age all on his own. In the search for one-of-a-kind human traits, culture seems like a good candidate.

It is true that human culture is peculiarly sophisticated. Yet many other group-living animals acquire skills from their fellows. To find some evidence of culture, we do not have to go all the way up to chimpanzees or elephants either. We can start with fish. Fish form groups primarily to mate or protect themselves from predators. Fish schools vary widely in size, from a few individuals going on a foraging trip, to hundreds of millions of herring, which seasonally gather into a great Atlantic shoal for breeding purposes (1). It is natural for such a species to learn to work with its group members.

It starts with something easy, like knowing how to respond to movements of other fish in order to keep the group swimming in a common direction. Then, it evolves into something more sophisticated, such as learning to fear predators not because they have attacked you, but because your friends act fearful every time they come around (this is done by releasing an alarm chemical, called the ‘Schreckstoff’, into the surrounding waters). Perhaps most interestingly, fish learn foraging strategies and techniques for catching food through imitation. When exposed to two demonstrators, they even learn to mimic the demonstrator with the more successful strategy. This last trick is the hallmark of cumulative cultural progress. Preferential copying of the most successful strategies lets everyone in the group benefit from the best new innovations, allowing the group to get progressively smarter and better adapted over time. So in the end, the ways fish group and learn together are pretty similar to the ways of small human tribes.

2. Mental time travel is another awesome skill.

It helps us plan ahead and learn from mistakes. The ability to reminisce about our past and to use remembrance to make plans for the future is closely related to the concept of episodic memory. A more familiar type of memory is semantic memory, which is required for learning facts about the world. Episodic memory differs from semantic memory by being uniquely personal. To illustrate the difference, ask yourself whether you can recall the capital of England. If the name London came to mind, you just successfully used your semantic memory. Now ask yourself if you remember when and where you learned that the capital of England was London. Don’t just say: it must have been in school. Try to cast your mind back to the specific moment in time when you first learned this fact and remember the specific circumstances surrounding the moment. If you cannot remember this admittedly mundane instance, think of something more salient, like when you first heard about 9/11. The experience of reliving your past in the present moment is what episodic memory is all about.

As it turns out, episodic and semantic memory reside in separate brain structures. Since the two memories appear not to be inescapably linked, scientists have naturally speculated on whether or not the capacity to store episodic memories is uniquely human. It is natural to wonder: what kind of relationships do other animals have with their past? We cannot ask animals directly, so scientists have settled on observational methods. Specifically, experimentalists have looked for behaviors requiring the ‘what-where-when’ triad. Once an animal knows which event happened where and how long ago it took place, it becomes at least possible to reminisce about subjective historical experiences (2).

A good example of a behavior requiring knowledge about what, where and when is food storage. Food tends to spoil and different foods do so at different rates. Pasta hangs around for years while yogurt typically needs to be eaten within a week of purchase. A hungry person has to recall what food he has stored, where it can be retrieved and whether or not the food is still safe to eat. The same thing happens with a hungry scrub jay (a small bird). Scrub jays cache both fast-spoiling meal-worms and more durable nuts. Jays can remember cache locations for weeks and successfully retrieve necessary items on demand. But if you keep a scrub jay from accessing its meal-worm stores for a few days, it no longer bothers to retrieve worms, because it knows they are spoiled. The jay even knows not to bother retrieving caches it was forced to bury while another sneaky jay was watching, since those caches are likely to have fallen victim to thieving by the spectator.

The tricky ways of jays are not conclusive proof of animal episodic memory, but they come pretty close. We can get even closer by recording electrical signals from resting animal brains. Recordings from rat brains indicate a strong tendency to constantly engage in mental replay of previous experiences just as humans do. This replay appears quite frequently when mice dream (activity recorded during sleep) or day-dream (neural activity recorded during quiet wakefulness periods). At this point, many of the original proponents have started recognizing that their initial theories about episodic memory being uniquely human were probably wrong. Many animals seem to have a sense of their own past, with the scrub jay being one great example of this.

3. Man does not get by on his own might, we make use of tools.

Throughout evolution, our tools have constantly increased in complexity. Starting with sticks and stones and ending with today’s power plants and computers, the growing sophistication of our tools correlates well with the growth of human civilization. Constructing a tool requires shaping an object with the purpose of using it later for a specific set of behaviors. Tool use is not a self-contained mental faculty like vision or memory is sometimes thought of. It is more like a good marker that many sophisticated mental processes can work together to build something new and creative. Like any other good skill, it has also been proposed to be the essence of humanity.

However, we know now that animal tool use is a rather common occurrence (3). Chimpanzees craft fine sticks with which they poke into termite nests to capture insects. Octopuses walk around with coconut shells, which they use as a makeshift shell to protect their soft bodies from attack. My favorite type of tool use is, however, meta tool use. Meta tool use occurs when animals utilize one tool to build or obtain a second tool, and only the latter one is used to do something directly useful, like foraging for food or maintaining a shelter. In one famous example, trapped ravens learned to obtain a long hook by pulling it close with a shorter hook that was lying around in their cage. The long hook was then used to fetch outlying items of food into the raven’s cage, which could not be retrieved with the original shorter hook.

We don’t have the space to go in detail through all the traits everyone has ever suggested as being uniquely human, so I want to mention just a few more key cognitive skills recently found to be present in non-human species: causal reasoning, theory of mind and language. All of this is important and rather complex stuff. Thinking about cause and effect, ‘entering’ into the minds of others and casual conversation all rank as some of the more sophisticated activities we may undertake daily. It now appears corvids have mastered causal reasoning, while chimps and even rats have empathy and a limited sort of theory about what might be happening in the minds of their friends and relatives. Even language has animal analogues among tweeting songbirds, yelping monkeys or sign-language-learning chimps.

If at this point you almost feel bored hearing about another amazing feat of animal thinking, I have achieved my goal. Animals can be super smart. Being smart is usually a great skill to have to survive in the complex and ever-changing wilderness. The larger point I would like to make concerns the gradual debunking of human exceptionalism. We have been too quick to declare anything concerning our minds special. More and more, scientists are thinking of human minds as having a strong evolutionary continuity with our animal ancestors. It still seems fair to say that our brains are animal brains ‘turned all the way up to eleven’. But the very fact that we can be placed on the same scale indicates how ‘typical’ we are.

So what is the secret sauce that makes human brains special? The truth is that we don’t know yet. It is still not clear how much more complex the human cognitive repertoire is when compared to a typical mammal. In fact, our brains might be less complex than those of other mammals in some aspects. For example, mice and dogs are certainly more adept at perceiving smells, while chimpanzees are reported to have larger working memories than humans (4).

When it comes to understanding complex systems, like the brain, our intuitions can fail us. We expect large cognitive gains to arise from large changes in brain architecture, but this may not be a necessary precondition for higher intelligence. It may well be possible to achieve unusually intelligent brains by packing many different, yet fairly typical, cognitive skills into a single brain. As we continue to ponder man’s place in the animal kingdom, scientists will undoubtedly advance many more hypotheses about the sources of high intelligence. Experience should teach us to be cautious about accepting any new explanations too quickly. The brain is still a mysterious organ and sometimes it is better to learn to live with a mystery than rush towards comforting but untested answers.

1. Webster M & Laland K (2011) From fish to fashion: experimental and theoretical insights into the evolution of culture. Philosophical Transactions of the Royal Society B 366:958–968.
2. Clayton N et al. (2003) Can animals recall the past and plan for the future? Nature Reviews Neuroscience 4:685–691.
3. Seed A & Byrne R (2010) Animal tool-use. Current Biology 20:R1032–R1039.
4. Kannan M (2014) Chimps outplay humans in brain games. Scientific American:  http://www.scientificamerican.com/article/chimps-outplay-humans-in-brain-games1/




Andres Laan studied neuroscience and physics for his undergraduate degree. He is currently investigating collective animal behavior at the Champalimaud Neuroscience Programme.



Edited by: Ivo Marcelo (section editor), Tiago Marques (section editor), Clara Howcroft Ferreira (editor-in-chief)
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