Out of Africa
Anthropology professor Martha Tappen investigates human evolution in Eurasia.
by Martha Tappen
The human and chimpanzee lineages split six or seven million years ago, but not until 1.8 million years ago is there solid evidence of human occupation of Eurasia. After some four million years of a geographic range confined to Africa, our lineage expanded north into Eurasia for the first time. Now humans are able to live nearly anywhere they want to, and with indoor climate control, high-tech clothing, and transport of food and goods across the globe, it is easy to see how we do it. However, apes are generally ecologically limited to areas with year-round leaves and fruit, and evidently, our australopithecine ancestors had only somewhat broader ranges than living non-human apes. What were the initial shifts in behavior, technology, diet, and/or social systems that allowed this first peopling of the more northerly—and no doubt more seasonal regions in Eurasia? These questions have preoccupied me for the last seven years since I joined the Dmanisi research team.
The Dmanisi site is an early Pleistocene site located in post-Soviet Georgia, situated at the geographic meeting of three continents: Europe, Asia, and Africa. Since 2001, I have excavated there with a team of colleagues from Georgia, America, Spain, Italy, and Switzerland, and we have recovered some remarkable finds, most famously five crania and post-cranial bones of a small early version of Homo erectus (sometimes called Homo georgicus). Georgia is a fascinating place to work, and I have been lucky to be able to bring a student from the University of Minnesota each year. Georgia is a fascinating place to work, and I have been lucky to be able to bring a student from the University of Minnesota each year.
I am in charge of the taphonomy of the fossil mammals, looking for clues as to how they may have died and who ate whom. I also look at the big picture from the site as a whole in an attempt to understand its position in the larger scheme of human evolution. My work has shown that the hominins at the site were eating meat, as evidenced by the presence of a few stone tool marks on the long bones of large extinct mammals such as deer and bison. Increased consumption of meat of large animals was probably critical in the ability of the hominins to occupy these northerly climes. However, most of the
thousands of bones at the site were not accumulated by hominins, but rather by large carnivores, such as sabretoothed cats and a large extinct hyena. The hominin bones themselves may have been accumulated by these large carnivores.
Much of the evidence indicates the hominins were not much different from their contemporaries in Africa. Their stone tools are broadly similar to those from Olduvai Gorge, and their brains were marginally larger than those of the later australopiths, but still half the size of a modern human. This past year we published an initial description of the post-cranial hominin remains from the site and the evidence shows, among other things, that the hominins were fully bipedal with modern human limb proportions, that they were rather short, and that some aspects of their post-crania were subtly different from our own, such as aspects of the shoulder.
It is intriguing that two of the five hominins recovered from the site appear to have survived into old age. If more individuals were surviving into old age, then there would have been a greater repository of knowledge and experience that could be passed on—and this could have made all the difference in terms of successful strategies for finding “fall back" foods, and dealing with lean years and difficult seasons.The increased survivorship of kin would have changed many aspects of social and economic interactive behavior, facilitating increases and changes in social-interaction, cooperation, reciprocity, food sharing, division of labor, and trade. These are behaviors that we know increased in human evolution, and would have changed in fundamental ways hominins’ interactions with the environment. The elders would increase the numbers of close kin within the group, promoting prosocial behaviors across generations in both directions. This hypothesis, which I call “The Wisdom of the Aged and Out of Africa I," is one of several that we are exploring.