Nature vs Nurture

Being a parent is hard.  Sometimes it seems that the rapidly expanding amount of knowledge about who humans are and how they are made is so overwhelming it is hard to know what is important for the health of their children and themselves.

For thousands of years, people have been in a discussion about “nature vs. nurture” particularly how it impacts human individuality, such as personality traits, intelligence, food preferences, fat or lean, musical ability, and even mental health.  Many smart people have debated whether individual traits and abilities are inborn (nature) or are instead forged by experiences after birth (nurture).

The rapidly advancing knowledge of genetics/genes gives them a very important role in individual differences but it certainly isn’t the only one.  At the same time as the rapid gains in understanding of human genetics is the rapid expansion of knowledge about the total combination of human body cells and the microbes living among them to make a functioning human.

In the book, I Contain Multitudes by Ed Yong, he states that the human body is composed of about 30 trillion cells and 39 trillion microbes.  He describes this relationship by imagining zooming in on skin and what would be seen: “spherical beads, sausage-like rods, and comma-shaped beans, each just a few millionths of a meter across.  They are so small that despite their numbers, they collectively weigh just a few pounds in total.  A million could dance on the head of a pin.”  He goes on to explain that most microbes are not disease causing but are invaluable parts of our bodies. “They behave like a hidden organ, as important as a stomach or an eye but made of trillions of swarming individual cells rather than a single mass.”

Our cells carry about 20,000 to 25,000 genes while all those microbes inside our bodies carry 500 times more making them able to quickly adapt to any possible challenge.  We know they help digest foods, produce vitamins and minerals, break down toxins and hazardous chemicals and protect us from disease from more dangerous microbes.

We know they affect our immune system and the development of the nervous system. Mice raised on normal chow given microbes from mice raised on a high fat diet became more anxious and had poorer memories.  Changing a mouse’s gut microbes can change their behavior.  There are numerous studies to determine if probiotics can reduce abnormal behavior in humans.

Humans gain their microbes from their mothers (vagina, skin, breast milk) and from their diet.  So far there has been limited success in developing a “probiotic” strain of microbes that remain living in a gut.  They can shorten bouts of infectious diarrhea or diarrhea caused by antibiotics. They can be successfully used in treating a severe diarrhea cause by Clostridium difficle (C-diff) by taking stool from a donor and placing all the microbes (fecal transplant) in the sick gut.

We have much to learn about nature.  Maybe through our gut’s microbes our diets can nurture behavior.

Published 12/04/2023

by Sally Robinson MD