Our churning bowels and stomach mimic a variety of inorganic environments in which a large range of bacteria have thrived for hundreds, if not thousands of million years. The stomach has low pH thanks to hydrochloric acid, sufficiently strong to make limestone fizz should you be unfortunate enough to throw up while collecting fossils. Parts of the gut are highly reducing, so that humans contribute their bit to global warming through the action of our symbiotic methanogen bacteria, although much less so than ruminant mammals which are major methane producers. We also host sulphate-sulphide reducing bacteria, with sometime spectacular effects in enclosed spaces. The animal gut has been around for quite long enough for internal bacteria to evolve and adapt to the dietary habits of their hosts, mostly as symbionts. However, some are pathogenic and infective. One pathogen in particular is not infective, so its effects have remained undetected until recently. It is now known that a major cause of gastric and duodenal ulcers, and digestive-tract cancers is the Gram-negative bacterium Helicobacter pylori. Massive doses of acid suppressants and bactericides effect miraculous cures on individuals who have had decades of misery from stomach pain. Now that the culprit has been fingered, you will not be surprised to learn that its DNA has been studied in some detail. The results are surprising (Falush, D. and 17 others 2003. Traces of human migrations in Helicobacter pylori populations. Science, v. 299, p. 1582-1585). Helicobacter is extraordinarily diverse, and regionally distinctive. Because it is pervasive, but not infective, the bacterium travels along with populations of its hosts, and is therefore a potential tool in tracking migrations. There are 7 geographically distinct H. pylori groups today, and their genetic structure can be traced to ancestors in Africa, Central and East Asia. Their geographic distribution matches those of human genetic and linguistic patterns, which have been attributed to the colonization of Polynesia and the Americas, to Neolithic migrations of agricultural peoples into Europe from the near-East, the expansion of Bantu-speaking people in Africa and to the slave trade.
The last ten years has seen enormous developments in understanding the first Europeans. So, a review of how they lived, how they differed from us, how they might have thought and how they came to an end shortly after our immediate ancestors turned up is very welcome (Klein, R.C. 2003. Whither the Neanderthals? Science, v. 299, p. 1525-1527)
The first volcanologists?
If there is ever a chance, the site that I would most like to visit is that discovered by Mary Leakey near Olduvai Gorge in Tanzania. A bedding surface in volcanic ash records footprints of two adult australopithecines and a juvenile who trudged together through fresh debris from a nearby volcanic eruption. The earliest and irrefutable confirmation of bipedalism, the tracks are also among the most poignant in the fossil record of humanity. Did this family survive the tragedy? The trackway is now covered to guard against erosion and theft. Altogether less heart-rending are younger footprints in an ash layer from the Roccamonfina volcano in Italy (Mietto, P. et al. 2003. Human footprints in Pleistocene volcanic ash. Nature, v. 422, p. 133), long known to locals as “devils’ trails”. The ash formed on the slopes of the volcano, as a pyroclastic flow, and the fossilised trail slopes at up to 80º. Because the ash is about 350 thousand years old, whoever made the prints were not fully modern humans, but probably ancestors of Neanderthals (H. heidelbergensis). The individuals had quite small feet, and may well have been children. The tracks come down the slope, both zig-zagging and showing occasional hand prints to steady the descent. They give the impression that whoever made them was not escaping an eruption, but having fun, much as kids today cannot resist hurling themselves down sand dunes and snow slopes. There is another possibility: curiosity drove them up the volcano after products of an eruption had cooled. Volcanologists cannot resist doing that either, and, as today, maybe they went up a little too early for comfort and had to leap for their lives.
See also: Muir, H. 2003. Earliest human footprints preserve prehistoric trek. New Scientist, 15 March 2003, p. 15.