An excerpt from Reconstructing Identity. A Transdisciplinary Approach. Chapter 4 Biological Identity by K.G. Moffat. School of Life Sciences, University of Warwick, Coventry, UK
If I had to think of the things that I would see as forming the basis of my own identity, then before I look at my genes I might consider the following statements.
I am as I write this middle-aged (55 years and counting).
I’m considered Caucasian, and I was born in Plymouth, in the UK.
Lessstraightforwardly, I consider myself Cornish because of my upbringing.
I had a Scottish father and a Cornish mother: what does that say about
my background, and how I view others and myself?
As a young boy, I was expected to attend a Methodist church with my parents, but I’ve
never believed in a god, and I am a confirmed atheist.
I am passionate about genetics, fruit flies, and spreading the message of science.
I used to play a competitive level of badminton and tennis, and I have always loved and played the guitar.
But which of these traits can be considered part of my biological identity?
Why was I good at racket sports but not good at athletics?
How come I could play the guitar but not the piano?
It’s the classic argument of nature versus nurture.
Is there a clear causative winner for anyone of my biological traits?
Do my genes determine my proficiency for sport, my abilities at the guitar, and my inabilities at the piano?
I would be of the opinion that for a few traits the answer is yes, and for many, often the answer is no, but most importantly, for nearly everything that I am and I do, both
my genes and the effect the environment has on my genes have a part to play.
Reproduction and You
There are currently just over seven billion people in existence, mostly on Planet Earth and a handful on a nearby space station. Most count themselves as members of a nationality, a faith, or a race. At least the majority can agree that each of us might be classified by a number of traits that we share with some common groups. Nonetheless, I suspect that we all consider ourselves unique. No one is like me and no one is like you. There never was and there never will be another you, nor me, not even if you have an identical twin, not even if someone achieves the science of human cloning.
When considering the issue of your biological identity, the combination of the particular egg and the particular sperm that generated you is the first issue; you are the product of a very particular combination. Your mother, when she was still a fetus in your grandmother’s womb, generated approximately six to seven million eggs. However, in human females, these eggs are continually lost in large numbers during development. Indeed, by the time your mother was born, she was already down to around one to two million eggs. More eggs are lost during the course of her life, and indeed from puberty onward, the human female will typically experience around 400 menstrual cycles during her lifetime (Wallace and Kelsey 2010). So which one of these 400 were you? Moreover, which one of the seven million eggs that your mother originally produced made it through to being you?
Now let us consider your father. As a male, I’ve often been told of course how useless men are, but if there is one thing we are good at, it’s making sperm. Males make them every day, from puberty onward for the rest of our lives and we do it by the million. While there are effects of aging on male fertility (Harris et al. 2011), nonetheless, estimates are that in a lifetime, we might make in the region of 250 billion! A geneticist refers to this production of eggs and sperm as gametogenesis, the making of
gametes. Each of these gametes, the eggs and the sperm from female and male humans, respectively, is unique and therefore it is, although simplistic, reasonable to calculate that you “are” because of a 1 in 100 trillion combinatorial chance, just by considering your two parents. We need to explain why each of these gametes is unique. The reason, of course, is our deoxyribonucleic acid, our DNA: the genes encoded within it,
the way they can vary, the means by which they can be shuffled to make new combinations, the way they can be altered by our environment, and the mechanisms by which the DNA is decoded. Of the roughly 108 billion people who have ever existed (Haub 2011), I am alone in being me, just like you.
Stripping Back Humans
Before we look at the makeup of genes, let us start by taking your average
human and do a rather grotesque imaginary experiment. Envisage that
you remove all the skin and throw away all the tissues and organs, leaving
just the skeleton. Can you now tell if the person was fat or thin, rich or poor, gay or
straight, black or white, Caucasian, or Asian? The answer to this for most
of us is no. If you were a highly trained anthropologist and had some clinical callipers, then you might be able to detect some differences in the mandible and skull. While it is reported in the scientific literature that these may be indicators as to race, this is still contentious. Perhaps more information can be gained from examining the bone’s microarchitecture: the density and the size of its inner porous structure. This has been used to explain the variation in fracture risks in different populations
A skeletal problem for biological identity? Can we really tell anything about our identity from looking at our skeletons? You would be able to tell the sex, the age, and obvious deformities. You might even be able to use the skull to try and recreate facial features from knowledge of anatomy. If we dug into the bone marrow, perhaps we could recover more cells and DNA that might tell us more. However, the extent to which the skeleton can reveal all the traits of a human being, including whether they were a “pirate” or not, is a matter of active debate.
Despite this, the simple answer is that as far as most of us are concerned, the skeleton on its own reveals very little information about ourselves. Let’s put the body back together again. In fact, if we were to do the experiment properly, we would need to take representative samples from each “race” and indeed for each trait, we wish to consider. As we look at these people, we notice many things—their skin colour, hair colour, eye colour, and so on. We might notice the size of their hands, their relative finger proportions, how tall are they, the shape of their earlobes, and their facial features. The list could be a long one. Look at yourself in the mirror. How far is it from the corner of your eye to the tip of your nose or what is the length of your philtrum, that little groove from lip to the nose? We call these traits anthropometrics, and these are the subjects of intense interest for facial recognition software (Vezzetti and Marcolin 2012). The example of our face tells us that for all these traits we might need to consider the genes in our DNA and the cells that they instruct to construct our appearance, our identity. It is worth looking more closely at the face: it is here that perhaps we pick up more information about our own identity and that of others. Given how many of us are so concerned about our appearance and because of our constant use of mirrors, we are familiar with our own facial identity.
But have you noticed how diverse human faces are? While the Daily Mail might report “Scientists discover nine face shapes” (Simon 2014), which the opticians Optical Prescription Spectacle Makers (OPSM) have been able to use for their commercial purposes, the reality is more complex and scientifically as yet unverified through peer-reviewed publication. If you compare humans to other animals, there is far more diversity within humans than in other species (Sheehan and Nachman 2014). Many of us will also hear the phrase “you ’re the spitting image of your: father, your mother, your brother, your uncle, your sister, your auntie, your grandfather” and so on. The reasons for both the diversity and the similarity are your genes, our species evolution, and the uses we as humans put our faces too.
Our Sexual Identity: The Role of the Chromosomes
In humans, females carry two X chromosomes while males have one X and one Y chromosome. I am a male because my Y chromosome carries a particular gene, the SRY gene. This gene makes a protein that instructs male fetuses to make testes. If you’re genetically male (XY) and lack this protein then you’ll develop a uterus and female genitalia, but you will not have ovaries. Males also exist who have two XX chromosomes but happen to carry a copy of the SRY gene. Although rare, this latter condition results in males who are again sterile as they fail to develop normal gonads. Human sexual phenotypes are hugely complicated. While we understand the basics of sexual development, and indeed what can biologically go wrong, we are far from understanding all the molecular biology, physiological and psychological effects in this area. For some biological researchers, their activity focuses on the search for the so-called gay gene, but intersex and transgender individuals are also of interest.
Potentially we could consider humans as three sexes: males, females, and intersexes. Intersex individuals are those who have features of both sexes, but true hermaphrodism (where an individual possesses fully developed testes and ovaries, breasts, and penises) is extremely rare. Clinicians usually advise parents of intersex babies to opt for a gender assignment and even surgery because the developmental psychology of the child is of paramount importance for sexual maturity, even if the individuals affected will actually be sterile. We have gained much biological knowledge from the study of intersex individuals, and it is clear that there is a range of phenotypes, some more female and some more male. It is likely that much is likely to depend on the status of the sex chromosomes, the SRY gene, and indeed variations of the genes that are controlled by the SRY-encoded protein (Blackless et al. 2000).