A Different Brain

 This is the first part of They Saw The Difference, announced here.

Dart’s original illustration of
the Taung child, 1925.

I have always told my students that the best actors go into law, the next best become teachers, and the leftovers go to stage and screen. The reader may justly conclude from this that when I teach (or write) I’m putting on a show.

About 1992, I prepared for work each day by slipping the fossilised toe-bone of a giant kangaroo into my shirt pocket, a child’s brain into one trouser pocket and its skull into the other.

<SFX> Brakes screech, voices off, shouting “Wha-a-at?”

To clarify, the skull and brain were fossils, 2 to 3 million years old, plus or minus a bit, and if the kangaroo toe-bone was real, museums around the world make casts of their best and rarest examples to sell to other museums, so what you see in a glass case or a lecturer’s hand is usually a copy, cast in resin from a mould of the original, and painted to resemble the original, which is somewhere safe. No matter, just having casts of the skull and part of its brain in my pockets allowed me to tell their story, as well as if I held the genuine relics.

Raymond Dart was an Australian teaching in South Africa in the 1920s. In 1924, he received two boxes of rocks on a morning when he was supposed to be getting ready to act as best man to his friend, Christo Beyers. Peeking into one of the boxes, he saw the cast of a brain lying loose, and in that, he saw something important.

Soon after the brain’s owner died, mud partly filled a skull, and this mud later hardened to rock. Technically, it was an endocast, a copy of part of the inside of the skull which closely reflected the brain, but it wasn’t any old brain—it was special, because of its small size and the position of its brain stem.

Interpreting fossils is an art and a science. Experts must know anatomy, how the parts work together, what small differences mean, and they work with those small differences. The position of the large hole in the skull where the spinal cord leaves the brain, the foramen magnum, was immediately obvious in the shape of the brain. Any animal with a brain stem like that had to have walked upright.

We cannot be certain how the Taung child died, but clearly the skull had ended up on its side in a lime-rich deposit, where the brain case was slightly more than half-filled with the mud which became the cast.

Dart saw that it fitted into a block of stone in the case, so a major part of the brain owner’s skull was probably there as well. He was a medical man, but fascinated by fossils, and he knew that this was important.  So was his friend's wedding, but afterwards, he itched to get back to his find.

The covering rock had to be carefully removed before the face could be examined, but a quick look at the cast was all Dart needed. The brain said this animal had a skull which attached to a vertical spine, lying directly below the skull, rather than behind it, as in chimpanzees and gorillas. The owner walked upright, like modern humans. Here is how Dart worked it out:

I was also convinced from the earliest period of my investigations that these creatures had placed great reliance on their feet for walking and running and that, consequently, their hands must have been freed for other tasks. This was implicit in the globular form of the skull which was obviously balanced on a more vertically placed type of backbone than that of a gorilla or chimpanzee. The improvement in the poise of the head implied a better posture of the whole body framework, since there must have been a relative forward displacement of the foramen magnum (the hole in the base of the skull which links the brain with the spinal cord).
—Raymond Dart, Adventures with the Missing Link, 1959, 11.

The people who interpret fossils work like Sherlock Holmes at his best. To those who can read, a glimpse of a document can be enough, but those who can read fossils can gain just as much from a single glimpse of just the right hint. At this point, Dart made a political mistake.

Even in the 1920s, a careful observer would have seen that the British Empire was already in decay, and there were few careful observers around, but there was a cast-iron rule: London is always right. When Dart reported his find in Nature in 1925, London came down on him like a ton of bricks.

His find (known as the “Taung child”, from where it was found and its obvious youthfulness) was small-brained and most British scientists were certain that any small-brained thing was no ancestor of theirs. Piltdown Man was the human beginning, they said: he had a big brain, and best of all, he was found in Britain! (There’s more on Piltdown in the Afterword, but you'll have to get the book to read that.)

Today, we might think Dart’s name for his find, Australopithecus (“southern ape”), was not the best name for an upright-walking individual, even one with a small brain, but Dart was trying not to draw too much fire upon himself. It didn’t work, but in the long run, the brain stem evidence held up and Piltdown was eventually shown to be a fake.

The true status of the Taung child lay hidden inside its jaw until 1987. In both humans and the other apes, the “adult” teeth emerge in a specific sequence. There is one order of appearance in humans, and a different order of tooth eruption in the other apes. Concealed inside the Taung child’s skull, teeth were erupting, and their pattern of development would tell us what the Taung child was, either human or ape. As there is only one Taung child, you cannot slice it up, just to see what is inside. You could take X-rays, but there is too much other material in the way, and the things we are looking for are much too faint.

For many years, it seemed as though we would never know what was inside the jaw. Then in 1987, Glenn Conroy and Michael Vannier had a bright idea. Instead of cutting the skull into thin slices, they made a series of virtual slices with X-rays, and fed the results into a computer, and used back projection to build up a three-dimensional picture of what was inside. Seeing how the Taung baby’s teeth were erupting would give the answer.

The researchers took their X-ray shots, just 2 mm apart, in three different dimensions: vertically, from front to back, vertically, from side to side, and horizontally. (They called it the sagittal, coronal and transaxial planes, if you prefer the technicalities.) The method is less important, but the answer was delightful:

…the Taung ‘child’ is not a little human, but just as important, it is not a little ape…
— Glenn C. Conroy & Michael W. Vannier, Nature 329, 625–627, 21 October 1987.

The whole answer was told in the differences: the Taung baby is a betwixt-and-between, a half-and-half, a missing link if you wish, and we would never have known if the two researchers had not decided to give it a CAT scan! Sadly, we had to wait another sixty years to find out what it was.

The story I told, over several years at the Australian Museum, was about how Dart saw a difference, and recognised a new scientific truth. This was just a few years after Conroy and Vannier had confirmed the role the Taung child’s people played in our origins, but there was more: I had human and gorilla skulls, that toe bone of the giant kangaroo and the matching bone from a horse. Always, it was about differences.

At other times, I talked to my audience about Edward Tyson (1651 – 1708), one of the unsung heroes of science, who persuaded Robert Hooke to pay seven shillings and sixpence for a 43 kg porpoise from a London fishmonger, so Tyson could dissect it. Back then, even experts like John Ray called the porpoise a fish, but Tyson’s Anatomy of a Porpess, published in 1680 showed the danger of judging a book by its cover. He said: “If we view a Porpess on the outside, there is nothing more than a Fish, but if we look within, there is nothing less.”

Tyson later dissected an infant chimpanzee which had died after being brought to London from Angola. While he referred to it as both a ‘pygmie’ and an ‘Orang-Outang’, the drawings show a chimpanzee, but Tyson’s book, filled with illustrations, showed for the first time just how close humans were to the other animals, and how they differed.

If Copernicus had removed the earth from the centre of the universe (something I describe in chapter 10), Tyson and his assistant, William Cowper, helped to remove Homo sapiens from a central position in creation. This change tied together humans and the whole of ‘lower’ creation. Tyson had taken one of the crucial steps towards recognising that evolution happened.

Next, back to Newton again…