Opinion – Suzana Herculano-Houzel: Gross mass first, thinking later

We humans love origin stories. Each different religion and culture has its own on the origin of the universe, of the Earth, of life, of the human being. Even Marvel characters have origin stories, which yield multimillion-dollar films, even repeated in parallel universes because otherwise Sony loses the rights to Spider-Man — sorry, I digress.

How we got here is one of those biology questions that hasn’t become a multimillion-dollar movie, but nowadays there’s a good chance it could become a pseudo-documentary series, especially with the ease of computer graphics special effects that can recreate times of life on Earth over the which we only know from fossils.

Fossils are the remains of creatures that lived at least ten thousand years ago, and usually several million years ago, in other geological eras (less than that, the rest are just called corpses anyway). Somewhere in the midst of these fossils are the remains of our ancestors.

The study of fossils by Paleontology is the most extreme, and extremely interesting, version of the “CSI: True Crimes” type investigations of modern times, where one tries to reconstruct the whole life of the dead from what is left of him. As in the increasingly high-tech TV series, paleontology also gains from modernity.

The use of computed tomography on fossil skulls, for example, has just generated a new milestone in our history of life on the planet. Ornella Bertrand and Stephen Brusatte of the University of Edinburgh in Scotland and their colleagues published a study in the journal Science of 124 fossils of mammal ancestors, including 34 young specimens from the dinosaurs’ first million years post-extinction.

As well as new evidence that changes the direction of the show’s investigation, the 34 new fossils illuminate the “immediately” post-apocalyptic-comet-that-destroyed-the-dinosaurs scene with an unusual revelation.

Until then, all stories about the origin of mammals like us started with tiny mammals, which escaped both the dinosaurs and their catastrophic extinction, and then grew in body and brain size at the same time. The logic was that bigger animals had the advantage by becoming more and more predators, not prey—and a bigger body must need a bigger brain.

The new fossils, however, clearly show that post-apocalyptic mammals first grew in body size — and only a few million years later did they have larger brains.

Body and brain, therefore, do not necessarily change together in size. “The increase in brain size was the product of increasingly fierce competition between larger animals,” the authors propose. I disagree. “The brain grew in size because it could, as life got easier with a bigger body,” I propose.

Who is right? Here’s another case for my detective agency—I mean, lab…