Speaking of self-repair, here's a fascinating new finding from Malin Hernebring in Sweden. Here's the technical paper, from a few years ago; it's part of Hernebring's Ph.D. thesis work. (Via Richard Dawkins's site.) As we age, our cells gradually decay; the DNA stays relatively intact, but proteins degrade with time. This is a big part of the aging process, leading to wrinkled skin as well as more serious consequences. When you think about it a bit, that raises a puzzle. A newborn baby arises out of the cells of its parents. So if the proteins simply decay without repair, every generation would get handed down a degraded set of proteins. At some point, therefore, there has to be some repair job, so that the baby gets fully functioning proteins. If this idea is right, you might guess that the repairs happen at the level of ovum and sperm; maybe when these cells are created, extra effort goes into tuning up their proteins into working order. But the new research says no -- it's actually after conception that the clean-up crew arrives. The newly conceived embryo consists of stem cells that soon begin differentiating themselves into the different kind of mature cells. It turns out that it's during this differentiation process that proteasomes go to work, breaking down the damaged proteins and generally tuning up the engine. (Maybe this is when the soul is implanted in the embryo?) The next obvious question is: why can't these cellular clean-up crews be active all the time? There are clear implications for studies of (and therapeutic approaches to) aging. Nature wants all the individual animal organisms to die, making room for new generations; but there's no reason we have to go along with the plan.