While I don't endorse his personally hostile rhetoric, biologist P.Z. Myers does a nice job of critiquing Ray Kurzweil's new claim that we may be only a decade or so from reverse engineering the human brain. Kurzweil is apparently basing his claim on the assumption that the design of the brain is encoded in the genome. Myers explains how wrong that assumption is:

[The brain's] design is not encoded in the genome: what's in the genome is a collection of molecular tools wrapped up in bits of conditional logic, the regulatory part of the genome, that makes cells responsive to interactions with a complex environment. The brain unfolds during development, by means of essential cell: cell interactions, of which we understand only a tiny fraction. The end result is a brain that is much, much more than simply the sum of the nucleotides that encode a few thousand proteins...

We cannot derive the brain from the protein sequences underlying it; the sequences are insufficient, as well, because the nature of their expression is dependent on the environment and the history of a few hundred billion cells, each plugging along interdependently....we have absolutely no way to calculate in principle all the possible interactions and functions of a single protein with the tens of thousands of other proteins in the cell!

I like Myers' description of genes: "A collection of molecular tools wrapped up in bits of conditional logic." It's not quite ready for a grade school text book, but it does nicely convey how dependent genes are on the outside world to produce anything of substance. We need more scientists suggesting more inventive new metaphors for genes and developmental biology.