The webcomic xkcd has many gems, but one my all-time favorites pokes fun at how teachers have a pechant for over-emphasizing the wrong-ness of a “misconception.” In an usually admirable but misguided effort to move students from a naive way of thinking, “overzealous” instructors salt the Earth so that no further thinking can occur in the “wrong” tracts. However, sometimes the most seemingly incorrect views reappear when least expected. One of the famous scientific controversies middle school biology students are taught regards the theory of Lamarckism, which essentially states that evolution occurs because offspring inherit changes that occurred to their ancestors. The classic example is of a giraffe, which is said to acquire a long neck from stretching for the leaves at the top of trees. According to Lamarck, this useful trait (long neck) is then inherited by its children. Ask any elementary school teacher about the “heritability of acquired characteristics” today, and you are overwhelming likely to hear stories involving mice getting their tails hacked off, but going on to give birth to normally-tailed offspring. Students get drilled into them the concept that only germ cells can carry heritable information, and that what happens to a organism during its lifetime has no bearing on the “book of life” it gifts to its offspring. But what if that book can have annotations? The growing field of epigenetics is showing almost daily that just a copy of the “instruction manual” is not enough to get through the business of living. Genes can be turned on or off, in way we are only beginning to fully appreciate. For example, all the cells in your body, whether nerve, muscle, lymphocyte or whatever, carry around a full copy of your DNA sequence. The assignment to become a certain cell type requires changes that “mark-up” the genes needed or not needed, depending on the jobs. This may be done with chemical tags; for example, adding a methyl group to a nucleotide base to change how its gene it encodes is expressed. We are finding that some changes, like the difference between worker bees as nurses or foragers, are reversible, or even heritable from your parents experiences.
While it may be important to replace naive conceptions of giraffes with more sophisticated ones, teachers often do a disservice to their students by “overselling” certain concepts. Because nature is (and must be) more complex than that.