Brian Clegg - What Do You Think You Are?

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I n the introduction to my 2012 book The Universe Inside You, I asked the reader to stand in front of a mirror and look at his or her body, using this experience as a starting point for an exploration of wider science. In What Do You Think You Are?, we are going to turn this idea on its head and go far deeper discovering the scientific basis of what makes you uniquely you. What makes you different from other humans, other animals, plants or even rocks. What is it that makes up the definitive combination of factors that is you?

There are huge similarities between humans, but each is a unique organism you included. So why is this the case? What makes you the way that you are and different from everyone else? These are questions that we can explore on a whole range of levels. It is easy but unrewarding to state that you are unique in some hand-waving fashion. For a clearer understanding we need to employ the tools of science. In his book The Scientific Attitude, Lee McIntyre discusses what distinguishes science from non-science or pseudoscience. He believes that it is the scientific attitude, made up of two simple components: empirical evidence (based on experiment or observation, rather than on theory or logic), and being prepared to change theories in the face of evidence that conflicts with them. To understand what makes you you, we need to employ such a scientific attitude.

Some would say that science is an unnecessary complication, because what make you the person that you are is your soul. Although in a number of countries the majority now have no religious belief, across the world well over half of the population are followers of one religion or another: religions that almost all say that there is more to a human being than can be explained by physical factors alone. Those holding such beliefs may refer to a soul, or a life force or a vital spark asserting that there is something more to the makeup of an individual human than physics and chemistry, an essential something that many believe transcends death.

There is no scientific explanation for this extra something but for the majority of believers, the concept of a soul or its equivalent goes beyond the physical: it is supernatural. As such, by definition the soul cannot be explored by science, as science is the study of nature. If you feel that ignoring the possibility of a soul limits our ability to truly explore all that makes you you, thats fine. Theres nothing in this book that actively counters the existence of a soul. But we can still make a fascinating journey into your individual existence based on what science is able to tell us about humans, where they came from and how they function.

At the most basic physical level, you are composed of atoms. Everything about your body, from the structure of your cells to the intricate operations of your brain, involves the interaction of atoms in both simple and complex molecules, providing a vast and intricate dance of cause and effect that comes together in the emergent principle we call life.

We perhaps should spend a moment on that e word emergent because it is a very important concept, not only when thinking about life, but also when considering other aspects of you, such as consciousness. Something is emergent if it comes into being as a result of the collective interactions of components, but isnt present in the individual components. Very few of us would consider that the atoms that make you up are alive yet collectively, the whole person certainly is.

Life, then, is more than a collection of atoms, which would still be the same atoms if you were minced up as fine as you like and put in a large jar (try not to think about that image too closely). But clearly you could not be the organism you are were it not for the right atoms being available to make you up. Each of the estimated 7,000,000,000,000,000, 000,000,000,000 atoms in your body has to have come from somewhere. And it will turn out that to reach you, each of those atoms has endured a remarkable journey through time and space.

In one sense, taking the atomic view of you we have to admit that you arent unique. There may be vast numbers of atoms in your body, in a unique configuration, but each atom 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 elses.

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 Earths 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 wouldnt 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.