Recently, I have been researching and preparing several science-y posts in an effort to make this summer vaguely worthwhile in light of imminent university applications. However, a couple involve biochemistry that I’d rather like to get my head fully around prior to writing. And I have still not got my hands on a pigeon stomach (not yet though, but soon…). However, I feel the overwhelming urge to write.
So this post has been something of significant interest to me, and was actually part of the driving force convincing me to study biology. Despite my admittedly minimal substantial research into the topic, I have presented my ideas at school, and thus consider my theories and conclusions to possess at least a shred of legitimacy. So I plant to share it with you guys!
I’ve just realised I need a graph. As I’ve not come across anybody who has made a similar graph, it is not on Google Images, and my computer skills have significant room for improvement, so I’m going to go ahead and describe it to you.
Okay, so imagine a simply double axis. The x-axis represents time, going from 7 million years ago right through to the present day. The y-axis represents the braincase volume.
For the sake of my argument, I have made two assumptions: the first is that as the braincase volume increase, the size of the brain also increases. Whilst this may not always be true, there seems to be no reason for this not to be true. After all, why should there be space in the braincase?
My second assumption is that as the brain increases in size, the ‘intellectual capacity’ of the organism possessing this brain increases. This is slightly more controversial, as it is shown that this is not always the case. Organisms such as elephants and dolphins possess bigger brains and, to our knowledge at least, they are not even close to being on par with our own intellectual capacity. However, we are only interested in the brains of hominids, so human-like species. 7 million years is most likely not enough time to allow complete evolution of brain, and thus neural, structure.
What is important in determining intellectual capacity is the folding of the brain. It is suggested that this capacity occurs as a result of electrical impulses down neurons in the brain, which possessing billions of these tiny structures. As the amount of folding increases, the surface area of the brain also increases, leading to the ability to hold more neurons, resulting in increased intellectual capacity. As the structure of human brains has not changed much in the past 7 million years, thus, my second assumption is legitimate.
Anyway, back to my graph! This graph is designed to plot the braincase volumes of the immediate descendants of our own species, Homo sapiens. This begins with an extremely ape-like species, Sahelanthropus tchadensis, 7 million years ago, which had a braincase volume of around 300ml. This remained pretty much constant, until about 2.4 million years ago.
This period of time led to the evolution of the Homo genus, which humans belong to. This was spearheaded by the species Homo habilis, Latin for ‘handy man’. Despite surviving for less than 0.9 million years, its braincase volume leapt from around 350ml to an astounding 700ml. This trend was maintained by Home erectus, the first human species to stand on two feet, whose braincase volume grew to around 1000ml, before reaching our immediate ancestors, Homo heidelbergensis, with a braincase volume between 1300 and 1700ml.
At this point, something very interesting seems to happen. Rather than continuing to increase, H. heidelbergensis splits into two species: humans and Neanderthals. We humans possess an average braincase volume of around 1450ml. However, Neanderthals had a braincase volume of over 1600ml! But only one of these species is alive today…
Having first drawn this graph, three questions came to mind:
1. What caused the dramatic increase 2.4 million years ago?
2. What caused the line to level off after the evolution of Homo heidelbergensis?
3. Why did humans survive instead of Neanderthals?
So I applied some rational thinking and logic to the situation, and these are my conclusions.
1. What caused the dramatic increase 2.4 million years ago?
There seem to be several reasons explaining this drastic development. However, I do not wish to bore either you or myself in details, so I will discuss one discovery, which seemed not only to be the driving force behind the other causes of development, but also any sort of human development ever. This discovery is the discovery of fire.
Professor Alice Roberts, in her wonderful documentary series Origins Of Us, carried out an interesting demonstration involving loads of carrots. The first part involved her eating a kilogram of raw carrots. Not only did this take her hours, but by the end of it her jaw was sore and was obviously worn out by the multitudes of crunching it had been asked to do.
The second part of her demonstration involved her eating a kilogram of boiled carrots. On the contrary to her previous encounter with carrots, the kilogram was eaten all in one sitting, and the strain on her jaw was significantly decreased. The nutritional content of both kilograms was essentially equal, yet the nutrients from one kilogram required lots of energy for digestion, and the latter required less. The overall net gain of energy will have lead to more growth which, inevitably, would have resulted in bigger, and better, brains.
This led onto another brilliant breakthrough: the invention of tools, more specifically the spearhead. These could be obtained very simply by simply bashing two rocks together. However, the possible uses of this tool are endless, particularly regarding hunting and gathering, a caveman’s two favourite activities. This resulted in a better diet, displaying a wider range of nutrients, thus leading to even more growth, thus leading to bigger brains, thus leading to better tools, thus leading to better food, and so on and so forth.
Hence the development! But it was not to last…
2. What caused the line to level off after the evolution of Homo heidelbergensis?
The answer to this question is a bit more simple: if the braincase continued to grow, the human species would die out.
Many people like to think that if humans kept on evolving, gradually we would become a race of Megamind-like creature with incredible heads. However, this poses several questions. For example, how much would our bodies have to develop in order to cope with the added size and weight of our new heads? or a more significant one, wouldn’t childbirth be impossible.
Fortunately, humans have evolved to maximise braincase volume. An example is that women have a wider pelvis, allowing the pelvis to cope with a bigger head during childbirth. Another one is that childbirth in humans is almost on the edge of being completely lethal, quite unlike any other species known on this planet.
This has lead to an interesting disadvantage, in that human babies are completely defenceless against the outside world, and possess no hope of surviving alone. This has led to a variety of social changes unique to humans, explained better by a social anthropologist.
There are also a variety of physiological traits which came about as a result of big brains. For example, babies are born with a hole in the top of their braincase. This allows expansion later on in development, allowing bigger braincases in the future.
And finally…
3. Why did humans survive instead of Neanderthals?
Again, a simple explanation (though maybe I won’t go on a weird tangeant this time…): Neanderthals became too big.
Being larger allowed them to possess much larger brains. However, a bigger body requires many more nutrients. As Neanderthals existed in the same time frame as humans, there was competition for resources. With their smaller bodies, paired with drastic climate change, resulting in the destruction of European forests, where Neanderthals were known to reside, humans were able to survive with less food, thus causing the Neanderthals to become extinct, leaving only us humans.
Another theory exists that the brains of Neanderthals were much less developed than ours, leading to much less complex communication techniques. For example, when a Neanderthal would say ‘Me want hunt mammoth’, a human would say, ‘Today, we shall hunt the sleuthing mammoth. Using our sharp spears, abundant cunning and striking good looks, we shall surround the herd of mammoths, thus trapping them, bestowing upon us a feast of juicy meat to satisfy our carnivorous wives’.
Though many parts of that script will be shamefully inaccurate. Ah well.
Given this ‘research’, I’d say there is one take-home lesson regarding evolution and natural selection. Natural selection occurs as a result of an evolutionary pressure, followed by the reaction of a species to this pressure. This may be as a result of height, colour, cunning, diet, immunity to a specific disease, or any variety of things.
Now take a look at humans. We do not seem particularly special. We’re a slow, lazy, smallish species, yet we have an undoubted dominion over the entire animal kingdom, from gorillas to parrots to fungi to spring onions. This has occurred as the result of only one evolutionary trait: ingenuity.
In terms of survival, ingenuity is awesome. In fact, it is so good, that all other traits become completely irrelevant.
Cheetahs are the fastest animals on Earth, right? Wrong. Humans have been able to travel much, much faster than cheetahs.
Giraffes are the loftiest animals on Earth, right? Wrong. Humans have gone much, much higher than giraffes. If there was a fruit in an tree to high for giraffes to reach, humans could reach it without any problem.
Humans are the only species to become totally adamant in any living condition on the planet, no matter how harsh.
So that is, finally, my important lesson to you all about natural selection for humans. Although we are actually pretty helpless, useless creatures on the exterior, inside, we are the most phenomenal, powerful thing to have ever happened, possibly to the universe. And that is something to wonder about.
My Factless Autobiography 