When you think of the word innate, what synonyms does your mind devise? Characteristic? Inborn? Inherent? Well, Professor Kevin Mitchell wants us to add being human and personality to this list. In his new book, ‘Innate’, Mitchell explores the possibility of our genome withholding the essential information that makes us, well, us.
Mitchell’s relationship with all things science began at a young age; he developed an interest in biology that was encouraged by his mother, who held a masters in biology teaching. Inspired by famous figures such as Jack Cousteau and David Attenborough, Mitchell pursued an undergraduate degree in genetics at Trinity. His passion for genetics was evident from the start of his career, describing the field as “the thing that held biology together”. In particular, the lectures he received from Professor Kevin Devine served as an inspiration for his specialisation in the field of developmental biology, which was the focus of his PhD at the University of California, Berkeley, and postdoctoral work at Stanford University. Upon his return to Ireland, his career developed from being Associate Professor in genetics and neuroscience, to fellowship, and more recently to the position of Dean of Undergraduate Studies.
“A copy of our genome exists in the 37.2 trillion cells of every human, and within this genetic code is stored instructions for building a human brain.”
In response to the question, “where in our brain do we store our personality?” Mitchell’s apt reply was was “there’s a lot wrapped up in that!” A copy of our genome exists in the 37.2 trillion cells of every human, and within this genetic code is stored instructions for building a human brain, which is distinct in morphology and connectivity from, say, a “chimp brain”. Described as a “mindless biochemical set of algorithms”, Mitchell proceeded to explain how the genome is expressed as a variety of proteins whose expression level is regulated in every cell; thus, in order for the cell to differentiate or turn into a certain form, into a muscle cell, for instance. To add an evolutionary layer to his explanation, Mitchell also explained how our nature contains a “prior knowledge about the world”, where the selective pressures on our ancestors have shaped the adaptation to our DNA, and hence, the nature of our brain circuitry which is encoded in our genome.
With evolution comes variation in gene expression, and this forms the fundamental theory for Mitchell’s research. The genetic programme for neural development involves variations in the genome and the regulation of protein production. For example, one cell type will produce more of a particular protein than another. This results in differences in our brain structure, function, and, ultimately, our behavioural traits.
“One cell type will produce more of one particular protein than another. This results in differences in our brain structure, function, and ultimately our behavioural traits.”
If the genetic programme is so central to our brain, why does it not independently determine the phenotypic outcome of cells? Professor Mitchell says that “even if it were possible that the genome could specify all those connections in detail, that would make it incredibly fragile and vulnerable to genetic variation, environmental fluctuations, and molecular noise”. However, since the genome does not exist in isolation in our cells, it can withstand the surrounding noise, and we obtain mutations as a result that are tolerated by natural selection. The best example of this is with twin studies: this noise, which encompasses protein collisions and movements, is what introduces variation into the phenotypic expression of twins, who should be 100% identical due to their identical genomes. This emphasises the intrinsically probabilistic nature of the genome – each time you run a copy of a genome, it will always turn out different. If you introduce genetic variation between two fraternal twins, for example, you can see how in combination with the probabilistic nature of our genes, humans can show a continuum of phenotypic variation in multiple features, including brain structure and psychological traits.
What are these psychological traits? Intelligence, kindness, bravery, and social proficiency are just some of the many traits desired by the human population. When we have the opportunity to artificially select for these traits in our progeny, to change their innate state, the concept of ethology must be considered. Human genomes can be assessed throughout our lives and during pregnancy in a process called “preimplantation genetic diagnosis”. The purpose of these assessments is to screen for variants, which increase our predisposition to a certain disease. The emergence of what Mitchell termed “consumer eugenics” – essentially the scoring of embryos so as to determine the number of genes they contain for favourable characteristics – is viewed by him as an increasingly concerning epidemic. “I think that there’s a lot of ethical and moral questions that need to be explored that have not yet been.” In an age that provides genotyping services for sperm and egg donors for traits that could enhance their progeny, it seems that Mitchell’s opinion has never held to be so true. “It’s happening already, we need to have a discussion about it.”
“The emergence of what Mitchell termed as “consumer eugenics” which is essentially the scoring of embryos so as to determine the number of genes they contain for favourable characteristics, is viewed by him as an increasingly concerning epidemic.”
However, personality and brain structure does not only vary from person to person, but can be subdivided into gender. Mitchell explained how the male and female brain differs on both a structural and molecular level, as a result of different chromosomal and hormonal presence. Thus, behaviours often differ from one gender to another, with males displaying different sexual mating strategies to females, which can manifest itself in traits as common as the increased tendency for physical aggression in males. Even personality traits have been discovered to vary: “There are, consistently observed across many countries, slight differences in mean scores in traits like extraversion, neuroticism, and conscientiousness,” although both distributions tend to overlap, Mitchell explained. Traits such as intelligence and even blood pressure, may vary between males and females, as a mutation in one of the male X chromosomes has a more significant contribution to the variation than a mutation in one of a female’s two X chromosomes.
Mitchell also explained that neuroplasticity amplifies our predispositions, as opposed to changing them: “As we proceed through life, our experiences are shaped by our innate predispositions, in ways that often tend to amplify these into habitual odes of behaviour.” So, if you are shy, you tend to have difficulty making friends, and do not associate with larger groups. Your innate wiring is what influences your decisions in life, and results in your behaviour and personality type.
Not only does the genome influence how you live your life, but also your subjective experience of the world. There are genes responsible for the correct neural circuitry laid down in a particular manner to achieve environmental perception, as a response to an external stimuli. When you look at an object, your recognition is the result of multiple cells recognising dots, shapes, and, in the case of humans, faces. Our perception is personal, embedded in our genome, where we have varying sensitivity to reward, threat, and punishment, among other things. This sensitivity is driven by the presence of “neuromodulators”, such as dopamine and serotonin, which “act as a gate on synaptic plasticity”, the way that neurons are in a constant state of activity flux and can adapt to change in response to external and internal stimuli.
From molecular to behavioural, all aspects of scientific study are considered in Mitchell’s core argument of “inherent genetic destiny”. Our genome codes the plan, but our experiences of development and opportunity is what completes the phenotypic result.
