The Evolution of the Brain, the Human Nature of Cortical Circuits, and Intellectual Creativity

The remarkable collective action of organisms such as swarming ants, schooling fish and flocking birds has long captivated the attention of artists, naturalists, philosophers and scientists. Despite a long history of scientific investigation, only now are we beginning to decipher the relationship between individuals and group-level properties. This interdisciplinary effort is beginning to reveal the underlying principles of collective decision-making in animal groups, demonstrating how social interactions, individual state, environmental modification and processes of informational amplification and decay can all play a part in tuning adaptive response. It is proposed that important commonalities exist with the understanding of neuronal processes and that much could be learned by considering collective animal behavior in the framework of cognitive science.

A three-dimensional counting rule and its integral test system, the disector, for obtaining unbiased estimates of the number of arbitrary particles in a specimen is presented. Used in combination with ordinary and recently developed stereological methods unbiased estimates of various mean particle sizes and the variance of particle volume are obtainable on sets of two parallel sections with a known separation. The same principle allows the unbiased estimation of the distribution of individual particle volumes in sets of serial sections.

In 1967 the Kibish Formation in southern Ethiopia yielded hominid cranial remains identified as early anatomically modern humans, assigned to Homo sapiens. However, the provenance and age of the fossils have been much debated. Here we confirm that the Omo I and Omo II hominid fossils are from similar stratigraphic levels in Member I of the Kibish Formation, despite the view that Omo I is more modern in appearance than Omo II. 40Ar/39Ar ages on feldspar crystals from pumice clasts within a tuff in Member I below the hominid levels place an older limit of 198 +/- 14 kyr (weighted mean age 196 +/- 2 kyr) on the hominids. A younger age limit of 104 +/- 7 kyr is provided by feldspars from pumice clasts in a Member III tuff. Geological evidence indicates rapid deposition of each member of the Kibish Formation. Isotopic ages on the Kibish Formation correspond to ages of Mediterranean sapropels, which reflect increased flow of the Nile River, and necessarily increased flow of the Omo River. Thus the 40Ar/39Ar age measurements, together with the sapropel correlations, indicate that the hominid fossils have an age close to the older limit. Our preferred estimate of the age of the Kibish hominids is 195 +/- 5 kyr, making them the earliest well-dated anatomically modern humans yet described.