What Do You Think You Are The Science of What Makes You You - Brian Clegg Page 0,1

of any particular chemical element is identical to every other such atom,‡ and the human body only contains a few dozen different elements. The fact remains, though, that your particular set of atoms is specific to you, each with its own fascinating backstory, were we able to trace that atom through a history that stretches across billions of years. Your exact mix of atoms will have many similarities to those of other humans, but still differs from everyone else’s.

Even the most reductionist scientist has to admit that a human being is more than a collection of atoms. You are alive. And all the evidence is that it was surprisingly soon after the Earth formed that life began. We think there has been life for around 90 per cent of the Earth’s 4.5-billion-year existence. How was it possible to go from an accumulation of dust and gases to the basics of life? For that matter, what is life? We wouldn’t be able to ask these questions without ourselves being alive, which is a state that appears to universally need water and energy – so we also need to explore where these essentials come from to help make you you.

The very earliest life forms were single-celled organisms like bacteria – yet we are far more than such a single cell, however varied bacteria may have become. The next step in discovering what you are is to trace the path from the earliest life to human existence, putting to rest along the way the idea of the ‘missing link’ between humans and our biological predecessors. Considering your evolutionary past this way inevitably brings in genetics. At first glance this seems to cut down on your uniqueness. You are somewhere between 99 and 99.9 per cent genetically identical to other humans. For that matter, you share about 96 per cent of your genes with a chimp and 60 per cent with a banana.

However, we need to be wary of allowing a reductionist genetics-based approach. Although, as we will discover, genes do have a very significant impact on what makes you the way you are, the comparison underestimates the differences other contributory factors make. You may have a high degree of genetic overlap with chimpanzees, yet there is no doubt that you are distinctly different from the other great apes. As we will discover, you might get a hint in the fact that you differ considerably more in your overall package of DNA, of which genes only form a tiny part.

We know that our species, Homo sapiens, has been around for over 200,000 years. Yet very recently on this kind of timescale, we have begun to have a huge impact on the world around us and have transformed the way that we live. Until a few thousand years ago, what made you you would have been almost entirely about biology: now it has to take in the constructed and technological world around you too.

And there’s more of you to be explored. Because there are intangible but essential aspects to what you are – your consciousness, personality and behaviours. At some point in our evolutionary history, humans gained consciousness, but exactly what this is and how it works is one of the greatest remaining mysteries of science. We all know (or at least we believe) that we are conscious, but pinning down what it is to say that you are conscious and how consciousness works scientifically is a huge challenge. Yet without consciousness, it’s hard to see that ‘you’ exist as an entity at all.

Personality and behaviour too are very significant factors. Anyone who has had a friend or relative who has suffered from a condition such as dementia where personality and behaviour are altered knows just how hard it is to cope with this change. These are fundamental aspects of what makes you you. For a long time, there has been an argument over the relative importance of nature and nurture in contributing to your individuality: how much these aspects of you are down to genetics and how much to upbringing. Now, as we shall discover, there is quantitative data that makes it clearer just how this inner ‘you’ was constructed.

COMING FULL CIRCLE

It might seem reasonable that we begin our exploration with those most basic components of you, the atoms in your body. Instead, though, we’re going to start with a very different, much more human approach. Throughout much of history, a person’s definitive position in the world was not drawn from molecular biology, psychology