Minori Shinya: Nurture over Nature?

2022/03/09

"Your face after the age of 40 is your own responsibility."

These are words my mother said to me when I was still a child. I have forgotten the circumstances under which she said them, but perhaps because I was so shocked—thinking, "Does parental responsibility (= genetics) just disappear!?"—this part alone remains in my memory. Regardless of whether it is true or not, my mother's words imply that the human face changes under the influence of the environment.

There are enough differences in our human faces to allow for individual identification. Those differences are created through an intertwining of genetics and the environmental influences we experience during our lives. It is not that I want to talk back to my mother, but I am currently searching for the genes that determine individual differences in facial features. Not using humans, but using medaka—small fish that swim in ponds and streams. Yes, there are individual differences in the head morphology of medaka as well. And just like in humans, we know that both environment and genetics are involved. That is why, to identify specific genes, we try to eliminate environmental influences by raising medaka in as uniform an environment as possible. Then, by examining the correlation between head morphology and genetic differences, we attempt to identify the genes.

However, the environment is not to be underestimated. Due to space constraints, there was a time when I had to raise medaka in an environment affected by the outside temperature. I raised about 60 genetically identical medaka (like clones) in two separate batches and collected data on their head morphology. When I compared the two groups just to be sure, a statistically significant difference was detected.

Since they were genetically the same population, any differences that arose were entirely environment-dependent. Upon investigation, I found that the average temperature during rearing differed by several degrees Celsius between the groups. It seems the difference in outside temperature led to a difference in water temperature, which in turn led to differences in the medaka's head morphology. In other words, I had not completely eliminated environmental influences. Of course, all the experiments conducted in that environment had to be redone (cries).

While quietly proceeding with my experiments, having long since passed the age of 40, I occasionally recall my mother's words that I mentioned at the beginning. Hmm, environmental influences really cannot be ignored... no, no, but there is definitely a genetic influence too. I continue to feed the medaka today, while reminding myself of this.