Our genetic heritage is not a blueprint or an algorithm.

Our genetic heritage is not a blueprint or an algorithm, as many biologists have imagined, but something else entirely. In fact, the human genome is less a script than a puzzle that gets harder the closer they look. Knowing the entire sequence — the order of all 3 billion or so of our DNA’s chemical building blocks, nearly fully deduced by the international Human Genome Project between 1990 and 2003 — hasn’t helped much. That investigation showed that barely 2% of the human genome consists of actual genes, the information-coding sequences of DNA. It’s now clear that understanding the human genome is no longer a matter of figuring out what each gene does. The deeper and much harder question is how those genes are used, or regulated, a question that seems to involve some and perhaps much of the rest of the genome. By switching suites of genes on and off, the many different cell types in our bodies can all be created from the same material. Cells also regulate their genes from moment to…