Skulls reveal the dawn of civilization

Bonobos are an example of self-domestication.— photo: special arrangement  

When and how did we humans turn “modern”, and technologically and culturally adept? This was the theme of a symposium held several weeks ago at the Salk Institute in California. Dr Ann Gibbons has given a lucid summary of the main conclusions of the symposium in the 24 October 2014 issue of the journal Science . The experts attending the meeting suggest that “self- domestication” turned humans into the cooperative species we are today.

Many animal species have formed a collaborative and cooperating groups or herds long before we humans even arrived on the scene. Look at the hundreds of fish, birds, foxes, or even primates such as bonobos. In unity is strength is an adage they discovered and found useful. In forming societies of this kind, each member of the herd had to cut down aggression, understand the value of tameness and the advantages of working as a team. What can be learnt and achieved as a team is far more than that by solo acts, and can be passed on to generations. There is thus an evolutionary advantage and progress through such “self domestication” of wild species into society.

Dr Gibbons, in her review, cities the work of Russian researchers who have worked on captive silver foxes and identified the elements of what has come to be known as the “domestication syndrome”. Elements of this syndrome in silver foxes are curly tails, shorter snouts, floppy ears and smaller skulls. Studies of this kind on animals (foxes, bonobos), looking at overall physical features such as the skull, have provided a way for anthropologists (people who study humans and our societies) to look at when and how we chose to “self domesticate” or tame ourselves to form societies.

Dr Gibbons mentions the work of Robert Cieri and others, which has appeared in the August 4, 2014, issue of the journal Current Anthropology (55, 419-442, 2014). Happily enough, this paper is downloadable free on the Internet. I did so and found reading it highly educative, and recommend it to readers. They carefully measured and compared the features of the skulls of archaeological specimens of the early humans (80,000 years old) with those of more recent (some 10,000 yrs ago, and some contemporary) ones. The sheer job of collecting thousands of skulls, measuring their shapes, dimensions, features of individual parts such as the brows, ridges between the eyes, shapes of teeth, size of the cranial part of the skull (which houses the brain) and so forth has been a gargantuan task in itself. But they persisted and found some remarkable differences of the human skulls over the millennia. The brow ridges above the eye have reduced over the years, teeth became smaller, the cranial volume came down (smaller brains), and the faces shortened over time. They have termed this set of changes in the skull, and thus the head itself, as “cranio-facial feminisation”. This is because they claim that these changes over the years have made the male faces look more like female ones. Over the last 80,000 years and particularly after the early, middle and late stone age era), we have become less “wild” and more “delicate”. Remarkably similar to what was seen in foxes earlier!

What can these developments in the physical anatomy tell us about the biology of the brain and the face? Studies on animals, for example dogs, have suggested that the genes that regulate robustness and aggression affect the facial shape. These in turn lead to lower levels of “aggression molecules” such as testosterone, stress hormones and changes in the action of neural crest cells leading to changes in teeth, muscles, bones and glands. See how much the skull can tell.

Such changes have not been sudden or rapid, but evolved over time. Growth in human population size, beginning about 200,000 years ago led to higher population densities, giving rise to the play of natural selection.

Humans started forming groups as early as about 68,000 years ago from Africa and began their long migration across the globe. In doing so, they formed groups or societies over millennia, settling down in various places across the world. Language, customs, social mores, culture, religions and technology began emerging. The main thread that bound each such society has been tolerance, cooperation and levelling down of aggression. This, in turn, Cieri and others argue, led to the evolution of technology —tools, taming and using fire, navigation, fishing and birding, water harvesting and agriculture — all over the millennia spanning the early middle and later stone ages ( almost until 25,000 years ago) Domestication of horse and cattle occurred. All this could happen because we self- domesticated.