I should have loved biology but I found it to be a lifeless recitation of names: the Golgi apparatus and the Krebs cycle; mitosis, meiosis; DNA, RNA, mRNA, tRNA.
In the textbooks, astonishing facts were presented without astonishment. Someone probably told me that every cell in my body has the same DNA. But no one shook me by the shoulders, saying how crazy that was. I needed Lewis Thomas, who wrote in The Medusa and the Snail:
For the real amazement, if you wish to be amazed, is this process. You start out as a single cell derived from the coupling of a sperm and an egg; this divides in two, then four, then eight, and so on, and at a certain stage there emerges a single cell which has as all its progeny the human brain. The mere existence of such a cell should be one of the great astonishments of the earth. People ought to be walking around all day, all through their waking hours calling to each other in endless wonderment, talking of nothing except that cell.
I wish my high school biology teacher had asked the class how an embryo could possibly differentiate—and then paused to let us really think about it. The whole subject is in the answer to that question. A chemical gradient in the embryonic fluid is enough of a signal to slightly alter the gene expression program of some cells, not others; now the embryo knows “up” from “down”; cells at one end begin producing different proteins than cells at the other, and these, in turn, release more refined chemical signals; ...; soon, you have brain cells and foot cells.