Pharyngula

Aaargh! Physicists!

I read this story with mounting disbelief. Every paragraph had me increasingly aghast. It’s another case of physicists explaining biology badly.

It started dubiously enough. Paul Davies, cosmologist and generally clever fellow, was recruited to help cure cancer, despite, by his own admission, having “no prior knowledge of cancer”.

Two years ago, in a spectacularly enlightened move, the US National Cancer Institute (NCI) decided to enlist the help of physical scientists. The idea was to bring fresh insights from disciplines like physics to help tackle cancer in radical new ways.

Uh, OK…I can agree that fresh insights can sometimes stimulate novel approaches. Cancer is an extraordinarily complex process, but maybe, just maybe, the scientists studying it are so deep in the details that they’re missing some obvious alternative avenue that would be productive to study. I can think of examples; for instance, Judah Folkman’s realization that inhibiting angiogenesis, the process by which cancers recruit a blood supply from healthy tissue, would be a clever way to attack cancers beyond just bashing the cancer cells themselves. But then, Folkman wasn’t ignorant of cancer…he came up with that strategy from a deep understanding of how cancers work.

So I’m doubtful, but prepared to read something that might be new and interesting…and then I read Davies’ suggestion. Gah.

A century ago the German biologist Ernst Haekel pointed out that the stages of embryo development recapitulate the evolutionary history of the animal. Human embryos, for instance, develop, then lose, gills, webbed feet and rudimentary tails, reflecting their ancient aquatic life styles. The genes responsible for these features normally get silenced at a later stage of development, but sometimes the genetic control system malfunctions and babies get born with tails and other ancestral traits. Such anomalous features are called atavisms.

Charles Lineweaver of the Australian National University is, like me, a cosmologist and astrobiologist with a fascination for how cancer fits into the story of life on Earth. Together we developed the theory that cancer tumours are a type of atavism that appears in the adult form when something disrupts the silencing of ancestral genes. The reason that cancer deploys so many formidable survival traits in succession, is, we think, because the ancient genetic toolkit active in the earliest stages of embryogenesis gets switched back on, re-activating the Proterozoic developmental plan for building cell colonies. If you travelled in a time machine back one billion years, you would see many clumps of cells resembling modern cancer tumours.

The implications of our theory, if correct, are profound. Rather than cancers being rogue cells degenerating randomly into genetic chaos, they are better regarded as organised footsoldiers marching to the beat of an ancient drum, recapitulating a billion-year-old lifestyle. As cancer progresses in the body, so more and more of the ancestral core within the genetic toolkit is activated, replaying evolution’s story in reverse sequence. And each step confers a more malignant trait, making the oncologist’s job harder.

I’m almost speechless. I’m almost embarrassed enough for Davies that I don’t want to point out the profound stupidities in that whole line of argument. But then, there’s this vicious little part of my brain that perks up and wants to leap and rend and gnaw and shred. Maybe it’s an atavism.

Please, someone inform Davies that Haeckel was wrong. Recapitulation theory doesn’t work and embryos do not go through the evolutionary stages of their ancestors. We do not develop and then lose gills: we develop generalized branchial structures that subsequently differentiate and specialize. In fish, some of those arches differentiate into gills, but those same arches in us develop into the thyroid gland and miscellaneous cartilagenous and bony structures of the throat and ears.

It’s better to regard embryos as following von Baerian developmental trajectories, proceeding from an initially generalized state to a more refined and specialized state over time. Limbs don’t reflect our ancient aquatic ancestry in utero, instead, limbs develop as initially blobby protrusions and digits develop by later sculpting of the tissue.

Sure, there is an ancestral core of genes and processes deep in metazoan development. But Davies seems to think they’re lurking, silenced, waiting to be switched on and turn the cell into a prehistoric monster. This is not correct. Those ancient genes are active, operating in common developmental processes all over the place. You want to see Proterozoic cell colonies? Look in the bone marrow, at the hematopoietic pathways that produce masses of blood cells. The genes he’s talking about are those involved in mitosis and cell adhesion. They aren’t dinosaurs of the genome that get resurrected by genetic accidents. but the engines of cell proliferation that lose the governors that regulate their controlled expression, and go into runaway mode in cancers.

But even if their model were correct (which is such a silly way to start a paragraph; it’s like announcing, “If the Flintstones were an accurate portrayal of stone age life…”), it doesn’t help. We don’t have tools to manipulate atavisms. We don’t see any genetic circuits that can be called atavistic. The Flintstones might have made record players out of rocks, but that doesn’t imply that the music recording industry can get valuable insights from the show.

Oh, well, I shouldn’t be so negative. I’m alienating possible sources of work here. I understand the physicists have encountered some peculiar results lately. Have they considered bringing in a biologist consultant with no prior knowledge of particle physics? I have some interesting ideas that might explain their anomalies, based on my casual understanding of phlogiston theory and ætheric humours.