Some brief half-thought-through notes on Paul Davies's delightful article in CiF today on cancer evolution. Davies describes his theory that the evolution of cancer is kinda the evolution of life in reverse: that cancer cells pick up the functionality that was lost over time, while losing much of what was gained. Wouldn't it be pleasingly neat and tidy if it were true?Evolution certainly is the overarching theory of cancer biology — as with everything in the life sciences — and it is indeed frequently the case that in cancers lots of cellular systems, like apoptosis, get deactivated, and some (near) vestigial systems can even become active. But it's just not as pleasingly simple as Davies would like. In addition to more recent systems getting deactivated, and redundant ones being reactivated, cancer cells pick up all sorts of adaptations, like hijacking* the system for growing blood vessels (angiogenesis) and evading or suppressing the processes which should clean up damaged cells. It's difficult to see how these fit in with a theory of regression. Even with the adaptations which do look like a regression, the look might be somewhat superficial: at the molecular level there are several ways for cancer cells to cope with hypoxia, for example, and they're not necessary quite the ancestral processes imagined. There is no "program": although selection will frequently favour the same adaptation (but not necessarily with the same underlying mutation/molecular system) in case after case if it's stumbled upon, the mutations themselves are pretty random and in every case different combinations of events happen and not necessarily in the same neat linear way. So in his conclusion, he's right that evolution has huge implications for therapy. Rather overstating things when he says cancer is a window on the past, I think:
The deep links between evolutionary biology, developmental biology and cancer have huge implications for therapy, and also provide an unexpected reason to study cancer. By unravelling the details of cancer initiation and progression, scientists can open a window on the past through which we can gain tantalising glimpses of life in a bygone age.
* if I can get away briefly with using the Davies-style language of ascribing purpose to this process.