午夜剧场

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

These are the words my mother said to me when I was still a child. I have forgotten the context in 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 the truth of the statement, 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 argue with my mother, but I am currently searching for the genes that determine individual differences in facial features. Not in 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 as with humans, we know that both environment and genetics are involved. This is precisely why, to identify specific genes, we try to eliminate environmental influences by raising medaka in as uniform an environment as possible. We then attempt to identify genes by examining the correlation between head morphology and genetic differences.

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 the groups were genetically identical, all the differences that arose were 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 a difference in the medaka's head morphology. In other words, I had failed to completely eliminate environmental influences. Of course, all the experiments conducted while rearing in that environment had to be redone (cries).

While quietly proceeding with my experiments, now well past the age of 40, I occasionally recall my mother's words mentioned at the beginning. Hmm, environmental influence is nothing to scoff at... no, no, but there is definitely a genetic influence as well. I continue to feed the medaka today, reminding myself of this.