Biology

What is a Human? Part Two

Part Two: What makes us Special?

If humans are just a product of billions of years of chemical reaction and evolution, then what makes us special? Some may argue that, in short, we aren’t. And it’s true that animals are not just reliant on instincts, with no emotion- people like Darwin, and later Jane Goodall have proved that statement wrong many times… But what other species has had the same magnitude of impact on the world as we have (perhaps early cyanobacteria, which supplied our planet with the oxygen that allowed life to form) How am I able to write this blog, extracting knowledge and words from a vast vocabulary I have retained over the course of my life, using a computer that sends signals to and from space!?

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An often cited feature is our brains: they are significantly bigger than those of other human species, brain size, or more accurately brain to body ratio is a somewhat good marker of intelligence. Brain size increased slowly in archaic humans slowly after they began to walk on two feet and use tools, and then this growth increased further after the departure from Africa because they would have been facing new experiences, requiring the need for problem-solving and critical thinking on a scale never before needed. But the most dramatic brain size increase was during a period of rapid climate change, for the same reasons mentioned previously. In particular, it is our cerebral cortex that is significantly larger than other animals: it is responsible for more complex cognition, and takes up 80% of our brain mass!

As well as evolutionary differences, it may be that our extraordinarily long childhood is the reason for our large brain size. For a chimpanzee, for example, the period of most rapid brain growth is before birth, and this growth slows immediately after birth. In humans, however, the brain continues to rapidly grow for over a year! On the other hand, primate’s brains are more developed at birth, whereas human babies have brains that are easily ‘moldable’! (Another reason to “stay in school, kids!”

Brain Growth of a chimpanzee showing rapid growth until birth, which slows and eventually levels off by 6 years old. The line as a whole stays relatively close to the x axis
Brain Growth of a Chimpanzee
Brain growth in humans showing rapid brain growth until just after a year after birth, which then slows but continues to grow past age 10. The line is significantly higher than on the previous graph.
Brain Growth of a Human

Despite this, the past 10,000 years have seen some decrease in brain size, which coincided with the agricultural revolution, when diets became more restricted and daily life became more repetitive. However, it is possible that this size decrease could just be ‘pruning’, making our brain more efficient! And in recent years, since the industrial revolution, our brain’s have slightly increased in size, probably due to better nutrition and schooling.

Yet having a larger brain is not necessarily helpful, as our brain only takes up 2% of our body mass, but uses 20% of our energy!

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It is probably due to this size and complexity that we are able to have such complicated languages with many synonyms, dialects and rules (if you have ever tried to a learn a new language, you’ll understand what I mean!), and many different ones within that! This may have been the reason we are able to work in large groups, communicating sophisticatedly. It meant that we were able to plan hunts and work as a team, to bring down animals much larger than us, many of which were dangerous predators themselves! It may also have lead to the decline of other human species, as it is possible that the Neanderthals died from mass genocide on our behalf…

On a slightly more cheery note, humans also form social groups with strong social bonds, and since the advent of social media, their enormity has only increased! Like with languages, there are many rules, and it is likely that this was the reason our languages grew to be more and more elaborate! This is because these groups had many rules and roles, and so required an extensive vocabulary and a larger brain to process the information. It is safe to say that the evolution of languages, brain size, and larger social groups are deeply intertwined! These social networks allowed resources to be shared, increasing rates of survival of the whole group. Living in groups not only allowed the sharing of resources, but also jobs and roles. It meant that a few people could go hunt a large animal as a team, and the rest were able to stay in relative safety. This meant that childhood could lengthen, as it was no longer a disadvantage to the group to look after her young instead of hunting, meaning that childhood could lengthen! Humans have the longest childhood of any species (please correct me if I am wrong), which allows time for the brain to grow! This correlation is proven by the fact that an Australopithecus has a childhood similar to the length of a chimpanzee’s (7 years or so), and has a similar brain size, whereas a Neanderthal, with a Brain Size more similar to ours, also has a similarly lengthed childhood.


It is undoubtedly true that no other animal (except perhaps the cyanobacteria and early organisms that flooded our atmosphere with oxygen) has changed the world as much as we have. Sure, various grasses cover most of the land, and phytoplankton/ cyanobacteria are found in every ocean and are important producers of oxygen and energy. But it is livestock cultivated by us that produce huge amounts of methane, our crops that take up space that was originally rainforest, and our industrialisation has caused the planet to warm a whole degree, sea levels to rise, and the percentage of Carbon Dioxide in the atmosphere surpassed 400 ppm in 2016.

Overpopulation not only puts pressure on our societies but requires greater and greater space to grow food and to live in, which puts pressure on entire ecosystems!

Our impacts on the environment are intertwined: overpopulation leads to greater industrial activity, which leads to greater pollution and climate change, which in turn increases global temperatures and ocean acidity. Over long timescales, this change would be considered part of normal fluctuation, but our impacts have mostly taken place over the last 300 years! (Normal fluctuations of this size take millennia…)

So what really makes us special? Random Mutations and Natural Selection allowed our brains to grow in complexity, and we have used this ‘feature’ to develop technology (from simple stone tools up to the latest iPhones,brain scanners and particle colliders!) , for our own growth, which I would say is inherent to all species (every species uses whatever they have at their disposal for the progression of their species/ life). Unfortunately, our (selfish?) growth was at the expense of the biosphere also known as Earth (!), but thankfully we are using that brilliant brain of ours to figure out how we can protect this environment!

Sources:

BBC Earth

Wikipedia

http://humanorigins.si.edu/human-characteristics

https://interestingengineering.com/10-ways-humans-impact-the-environment

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If you can’t trust an atom… trust in science!

☆it’s like magic, but it’s true whether you believe in it or not!☆

See you next time!

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