Children environment genes Teenagers

Kids are genetically similar! No, all kids are genetically different!

March 25, 2015

The argument

Here’s John at consultation, father of 14 year old Jade, and 10 year old Mathew, with reference to Jade: “Teenage girls are all genetically the same. They behave the same, they look the same, they sound the same, and they all change friends as frequently as they change their clothes.”

Here’s my  next client, Emily. She’s the mother of Lance, 8 years, and James, 10 years: “Everybody’s different. No two humans are genetically alike.  I like the fact that Lance is so different from other kids. I don’t want him to be a cookie-cutter kid anyway.”

Who’s right? Are kids all the same (John) or are they all different (Emily)?

  4  points to consider before picking sides

  1. The human species is quite homogenous. We share more than ninety-nine percent of our genes. This figure explains why in general, we look quite alike: two arms, two eyes, a nose, a digestive and visual system, and brains that look remarkably alike.  We develop quite similarly too: most of us walk at around 1 years of age and put two words together by about 2 years of age.
  2. The differences between us are in the details. But, with so many genes in common, why would there be any differences at all?

Clearly there’s a paradox here. We share almost all of our genes, yet there are clear disparities between us.

3. To partially explain how the apparent contradiction works, here’s one way to think about it. Compare a gene to a string of say, green beads on a necklace. One person’s necklace might have a few green beads that are slightly lighter or darker or slightly different in shape than the next person.

If the string of beads was a gene, the differences in shape and colour could produce the variations between us; say, hair and skin colour. The genetic variants are called alleles. There are relatively few of them at birth, but their effects make an impact. Alleles that dominate can make us polymorphic, or  inwardly and outwardly different.

When allele variations in form and function are passed from one generation to the next, they can result in differences called phenotypes, or observable appearances. An example of a phenotype passed down from one generation to the next is the epicanthic fold seen in the eyelids of many people of Asian descent. Those who might believe that this is a racist observation are confused about the difference between a phenotype and a stereotype.

Often we might differ from one another because of differences on a single gene here and there.  Yet many important characteristics that vary  in degree – like height, intelligence, personality and the peculiarities of Lance’s and Jade’s  behaviour  (above) – occur when a number of genes interact with each other and with the environment. For instance, a well nourished Dutch child may have a genotype for tallness (the Dutch have a genetic propensity to be tall) and play basketball for Holland. But,  his undernourished countryman with the same propensity may be phenotypically short as an adult, and not make the local team. This fact highlights how environmental experiences can switch on and off particular genes for particular traits. John and Emily might be interested to know that even their parenting styles can influence their children’s in this way.

4. So, while genetically speaking, humans are very similar, in particular, we’re  different from each other. Our unique genetic outcomes make us unique. This is true of siblings, and true for people like Jade and Lance,  who live within the same culture. And,  like those cultures with epicanthic folds – or not, and those that are characteristically tall  – or short, cultures can differ from each other.

But, it’s still important to note that our common genetic outcomes and common world determine that we’re one species.  Above all, we humans vary most from other species, even when compared with our closest cousins, the great apes. We’re genetically human, and they’re not.

So, John and Emily both have a point – to a degree.

Names, locales, people and incidents have been fictitiously created by the author. Any resemblance to actual people, places or individuals is completely coincidental.

 

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