The Contextually Dependent Brain Part 1

Understanding Nature vs Nurture Through Genetics: Part 1

For as long as I can remember studying development, there has always been a debate called the nature vs nurture debate. This is a centuries' old debate on whether we become who we are as a result of our nature (we were always meant to be this kind of person and nothing can change that) or as a result of our nurture (everything a person is and will ever become is 100% dependent on the way they are raised; the environment and care that they receive). For decades there have been firm believers on either side of this debate.

Nowadays, however, there has been more of a shift to a middle-ground. An increase in research, especially genetics, has begun to show us that it's not a matter of a person becoming who they are due to nature OR nurture. Rather, it is an interplay between the two, a give and take between a person's biologically determined nature and the environment they grow up in. I am very thankful actually that it is this way because it means that no one is ever condemned to a certain negative future just because of their genetics or their upbringing. There is always room for change. This two-part piece emphasises that interplay of biology and environment at the genetic level. This first part looks at biology/genetics, and the second part looks at genetics and the environment.

Genetics, DNA, and Heritability

Let us first clarify some of these key terms. Genetics is the study of genes and DNA. DNA is basically like an instruction manual on how to build a human and it exists in every person, making them unique. DNA contains an assembly of all the information on what a human should look like and what they require to qualify as a functioning human. A DNA strand/sequence (like the one included in the image above), is made up of many genes all in different pairing and organisations. These genes all carry different bits of information and functions, and they come together to form the DNA strand.

If DNA is the instruction manual, then genes are the words and letters that make up that manual. So, genes are the individual building blocks that make up the DNA strand and they can cause development to happen. Every human's DNA is different. This difference comes from their genes. When two people come together to make a baby, that baby gets different genes from either parent, this is where inherited traits within families come from. It is also one reason that every human is unique. Therefore, genes can determine some inherited characteristics, as well as guide development and be influenced by the environment.

If we're thinking of genes as the words and letters, we can also consider the idea of "genetic variation". Genes can come in various pairings, similar to how you can put different letters next to each other to make different words. The letters themselves don't change, but their arrangement does. The same with genes. You can have one gene that can exist with different others and each of these groupings will lead it function in a different way. This concept is called genetic variation. Sometimes when you type a word, you make a typo. This typo can either create a new word (e.g sin, sip, bin) or create a mistake or non-existent word (e.g. sib, sie, qin). Genes can vary in good and bad ways too. Sometimes, the same gene can function in different ways as well (similar to homonyms in sentences - the same word can have different meanings). Other times, the gene functions in a way that is negative for development.

The key thing to understand with this though, is that a person's genes/genetic code is designed to create a fully functional brain, but it also relies on the environment to make that plan a reality (very similar to the stimulation I spoke about in Part 3). For example, somewhere in the genetic code is something that says: this person needs a brain that can do xyz. The genes and the neurons will get to work and build a brain that has the capacity to do xyz, but whether it actually does xyz and does it well can be very dependent on the external environment.

Heritability

Now heritability is a way of trying to understand how likely a child is to inherit something from their biological parents versus the environment around them. These can be physical characteristics like eye colour, shapes of body and bodily features, height; hormonal behaviours like baldness, metabolism, regulation; or more abstract characteristics like intelligence, "nurturingness", communicative ability or disorders. These heritable qualities are where we get the idea of being more “predisposed” to one thing or another. Some things can be more heritable than others, for example, eye colour or hair texture and this depends on genes.

However, heritability cannot predict any of this at the individual level, only a population level. It does not say that a specific outcome in a person (like height) is 90% genetic and 10% environmental. Rather, it says that in a population of x amount of people, perhaps 60% of differences in height within that population can be described by genetics. But it cannot always pinpoint exactly which gene. It's a complex idea, so it's okay if it's difficult to understand the first time.

Proteins

The last thing I want to touch on is proteins. These are not proteins like what we find in meat or eggs. Proteins, when we discuss genetics, is a molecule that is "created" or "expressed" by a gene. I have mentioned how genes direct development, but something has to carry out the task. So, if DNA is the manual and genes are the letters and words in that manual, proteins are the workers who must now carry out the task of building whatever they have been instructed to. Similar to neurotransmitters which have different functions.

There are proteins for almost every function in the body. There are proteins to move things around the body (like proteins for blood), to physically build up some parts of the body, others may help the body co-ordinate. Some regulate the body at the DNA level, others regulate it at the hormonal level. Other proteins trigger biological process and reactions in the body and brain. They all have an important purpose, and they are all influenced by how the gene behaves.

The Takeaway

Genetics is a complex topic, and I am no expert in it, so I have covered the very basics of it. However, it is not a subject which is easy to draw conclusions from. At every level of genetic study, there are many things to consider. This makes it difficult to draw definitive or causal or predictive conclusions about who someone will become from just genetic information. But like I said, this is also a beauty in it because it means that no person, no child, is ever trapped or confined to a specific future just because of their genetics. These concepts of the role of genetics in child development are really shown in later Issues, especially Issue 7.

In the next section of this two-part piece, I cover the idea of gene expression and epigenetics. This really shows how the environment comes in.

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