such as face shields are classified protective accessories. At the far extreme, self-enclosing diving suits or space suits are form fitting body covers, and amount to a form of dress, without being clothing per se, while containing enough high technology to amount to more of a tool than a garment. This line will continue to blur as wearable technology embeds assistive devices directly into the fabric itself; the enabling innovations are ultra low power consumption and flexible electronic substrates. Clothing also hybridizes into a personal transportation system (ice skates, roller skates, cargo pants, other outdoor survival gear, one-man band) or concealment system (stage magicians, hidden linings or pockets in tradecraft, integrated holsters for concealed carry, merchandise-laden trench coats on the black market — where the purpose of the clothing often carries over into disguise). A mode of dress fit to purpose, whether stylistic or functional, is known as an outfit or ensemble. Origin and history Early use Scientists have never agreed on when humans began wearing clothes and estimates suggested by various experts have ranged greatly, from 40,000 to as many as 3 million years ago. Recent studies by Ralf Kittler, Manfred Kayser and Mark Stoneking—anthropologists at the Max Planck Institute for Evolutionary Anthropology—have attempted to constrain the most recent date of the introduction of clothing with an indirect method relying on lice. The rationale for this method of dating stems from the fact that the human body louse cannot live outside of clothing, dying after only a few hours without shelter. This strongly implies that the date of the body louse's speciation from its parent, Pediculus humanus, can have taken place no earlier than the earliest human adoption of clothing. This date, at which the body louse (P. humanus corporus) diverged from both its parent species and its sibling subspecies, the head louse (P. humanus capitus), can be determined by the number of mutations each has developed during the intervening time. Such mutations occur at a known rate and the date of last-common-ancestor for two species can therefore be estimated from their frequency. These studies have produced dates from 40,000 to 170,000 years ago, with a greatest likelihood of speciation lying at about 107,000 years ago. Kittler, Kayser and Stoneking suggest that the invention of clothing may have coincided with the northward migration of modern Homo sapiens away from the warm climate of Africa, which is thought to have