History in skulls

7 August 2013

Over the past three years, PD Dr. Holger Herlyn of the Institute of Anthropology at Johannes Gutenberg University Mainz (JGU) has assembled a modern teaching collection of replica skulls that document the development of human beings and their relationship to other primates. The exhibits in the collection's display cabinets are ready to be investigated by the probing hands of the students.

Dr. Holger Herlyn sits at his desk. He has placed the 50,000 year old Neanderthal skull from La Ferrassie in France between his knees so that his hands are free. For the purposes of comparison, he holds up the far smaller skull of an Australopithecus africanus, a hominin that lived approximately 2.5 million years ago in Africa.

At the moment, Herlyn holds both fossils upside down so that the openings at the base of the skulls can be seen, the so-called foramen magnum, which once was at the end of the spinal column. In the Australopithecus skull this opening is much further back than in the case of the Neanderthal, in whose case it is much closer to the jaw.

"This tells us something about the gait of the two," says anthropologist and evolutionary biologist Herlyn. The Neanderthal walked upright, with his head held high. "Species such as Australopithecus africanus were able to walk upright but not to the same extent as Neanderthals and other species of hominins."

Homo sapiens and other primates

The skulls that Herlyn is handling are actually replicas although they look just like the real thing. The smallest details have been reproduced in these modern plastic models. Every nuance of color, every irregularity, every slight fracture is the same as in the original.

"Our collection is not valuable in a material sense," explains Herlyn. "In principle, these replicas are available to anyone." At the same time, however, the skulls are absolutely invaluable teaching aids. Herlyn's office contains both an original human skull (Homo sapiens) and some three dozen of these replicas. The collection not only documents the course of evolution up to today's human beings, but also includes examples of close relatives of man, such as marmoset and rhesus monkey.

Thanks to the osteological teaching collection at the Institute of Anthropology, Herlyn can make three important subjects tangible to his students. "Firstly, we can reconstruct the inter-species relationships. Most people don't know that chimpanzees are much more closely related to humans than they are to gorillas. Research proved this some time ago, but the way the relationship is depicted in the media is often very confusing and even creates the impression that human beings have evolved from chimpanzees.  It may on occasion be merely a question of semantics, but this concept is actually misleading. We are not descended from chimpanzees. We have common ancestors."

When monkeys laugh

The question of what we share with other species encompasses the second range of aspects that the students can use the teaching collection to explore. Herlyn has yet another example and skull at hand. "When we see a person laugh, we first see the flat front incisors. Such teeth appeared very early in the primate phylogenetic tree and are today present not just in humans, chimpanzees, and gorillas but also in New World monkeys, rhesus monkey, and others. Based on what we now know, such teeth are an evolutionary innovation in the so-called higher primates (Anthropoidea)." The anthropologist uses his finger to trace the incisors in the delicate lower jaw of the skull he is holding.

The third important topic is the development of humans and all that it entails. The erect gait, the expansion of skull size over hundreds of thousands of years, and the changes to the jaw – all of this and more can be deduced using the example skulls.

"One evolutionary characteristic of our species is the jutting chin for example." Herlyn picks up the Neanderthal skull again. The skull from Le Ferrassie does not have such a chin. The original of a more recent skull of our species shows a marked jutting of the chin. "We can only guess how this feature developed. It may have been a form of sexual selection. At some point, the mutation occurred and was seen as attractive."

Old plaster models next to new plastic ones

About three years ago, Herlyn started the teaching collection of replica skulls. Most of it is kept in one of the seminar rooms in the Institute of Anthropology's new building. Everything is still white, fresh, and almost pristine – except for the older display cases containing the roughly 100 skulls.

The cases also contain the plaster models that students once used for study. The old models look crude and unrealistic when compared with the new ones, their coloration leaves a lot to be desired.

To illustrate the differences, Herlyn chooses the tiny skull of a member of the wet-nosed primates (Strepsirhini). The lemur’s lower jaw has a ridge of teeth that jut forward, a feature that is smaller than a human fingernail. Tiny grooves, barely visible with the naked eye, show that the ridge is composed of six teeth. "You can only see such detail in modern replicas."

Skulls provide much information

The teaching collection is popular. "The sessions are integrated in a practical course in which the students primarily undertake laboratory research at the molecular level. So it's a nice change for the students to have larger objects in their hands once in a while."

Of course, Herlyn knows that molecular genetics has made significant contributions to answering questions of how human beings evolved and on the interrelationships between primates. "But bones also provide important information." Once again the anthropologist has picked up a replica, this time the skull of a tarsier. "For a long time it was unclear whether tarsiers were more closely related to wet-nosed primates or the Anthropoidea and thus human beings." Molecular genetics then proved that the higher primates were the closer relatives.

"Once you know this, it is easy to find anatomical evidence that the tarsiers belong in the primate phylogenetic tree." Herlyn points to the large plastic eye sockets. "See, a closed eye socket – just like that of a human being."