Christopher Seddon - Prehistoric Investigations: From Denisovans to Neanderthals; DNA to stable isotopes; hunter-gathers to farmers; stone knapping to metallurgy; cave art to stone circles; wolves to dogs

Imagine an iceberg where not ninety percent but all bar less than one tenth of one percent lies below the waterline. This tiny fraction represents what we term recorded history, or about six thousand years. The remaining six or seven million years is prehistory: a vast period of time that begins with the emergence of the first two-legged apes and ends with the rise of the first cities and states.

In my first book, Humans: from the beginning, I attempted to present a complete history of the human world up to the time of the first state-level societies. The result, inevitably, was a sizeable volume which although well received requires a significant commitment on the part of the reader, and might not appeal to somebody who wants to just dip their toes into the field of human prehistory. It is for such a reader that this much shorter work is intended. Here, the human past is presented in fifty short chapters. Although they are arranged in roughly chronological order, they are more or less self-contained and may be read out of sequence. I felt that this was a better approach than trying to produce an abridged version of the earlier book. Inevitably, there is some overlap between the two works (which are after all dedicated to the same subject), but I have also included a number of topics that were not covered in Humans: from the beginning.

Within my lifetime (which admittedly now spans sixty years), our knowledge the distant past has been greatly increased by modern science. The invention of radiocarbon dating in the 1950s essentially rewrote the prehistory of Europe. More recently, genetic techniques have demonstrated our close evolutionary relationship to chimpanzees, and the recent African origin of modern humans. It has confirmed that our ancestors interbred with Neanderthals and revealed the hitherto-unsuspected existence of the Denisovans, an archaic human species that also interbred with modern humans. Much vital albeit less headline-making work is carried out using methods that would not be practical without computers. We should remember, though, that the study of prehistory is a fairly recent discipline. That there was even such a thing as prehistory was not widely recognised until the mid-nineteenth century.

Human evolution and prehistory is now a fast-moving and dynamic field. Even in the short time since Humans: from the beginning was published, there have been a number of epochal discoveries. The date for the emergence of the first humans has been pushed back to 2.8 million years ago; we now have stone tools that were made by our even more distant, more apelike ancestors; we have fossil evidence that modern humans were in China 100,000 years ago, finally putting paid to the notion that modern humans did not leave Africa until around 60,000 years ago. Not least of all, there has been the dramatic announcement of Homo naledi, a primitive human species discovered in the depths of the Rising Star cave system in South Africa. Homo naledi wasnt even the only new species announced in 2015. These discoveries were widely reported in the media, reflecting the level of public interest in our origins and our past.

This book, like its much longer predecessor, is concerned with a grouping of two-legged apes known as the hominins, of which modern humans (Homo sapiens) are but the most recent. The first hominins emerged in Africa around seven to eight million years ago, when our distant ancestors diverged from those of our closest living ape relatives, the chimpanzees. Although we are now the only hominin species in existence, for most of that long period there were several. Even our species has shared the planet with Neanderthals and other archaic humans for much of its existence.

Not all of these hominins were our direct ancestors; many were evolutionary cul-de-sacs that died out completely. Rather than an orderly procession of ever-more advanced species, leading inexorably towards Homo sapiens, the hominin family tree has been likened to a tangled bush. The exact number of hominin species within this bush remains uncertain. The first and most obvious reason is that many hominin species almost certainly remain undiscovered. Less obviously, perhaps, palaeoanthropologists frequently disagree on just how many distinct species are represented by the fossil record. The two rival schools of thought are commonly known as lumping and splitting: lumpers try shoehorn as many fossils into a single species, while splitters do the exact opposite and proclaim new species and even new genera for each new fossil discovery. For example, a splitter is likely to see Homo ergaster, Homo georgicus and Homo antecessor as separate human species, but to a lumper they are all regional varieties of Homo erectus.

What is becoming clear is that after the hominin line split off from the chimpanzees, it went through three main phases of evolution. The first phase lasted from around seven up to 4.2 million years ago and the hominins of this period may be thought of as dual-purpose apes. Their brains were no larger than those of chimpanzees, and they were adapted for both tree-climbing and two-legged walking. Fortunately, there is a remarkably-complete hominin skeleton from this period, belonging to the species Ardipithecus ramidus. The 4.4-million-year-old skeleton of a female, popularly known as Ardi, was discovered in Ethiopia in 1994, and has greatly increased our knowledge of this period of hominin evolution. Ardi retained tree-climbing adaptations including an opposable big toe and thumb; later hominins retained only the opposable thumb. Subsequent discoveries included an earlier Ardipithecus species, Ardipithecus kadabba, which lived from 5.8 to 5.2 million years ago; and two even earlier species, Orrorin tugenensis and Sahelanthropus tchadensis. The latter may push the hominin fossil record right back to the split with chimpanzees.

The hominins of the second phase which lasted from around 4.2 to 2.0 million years ago are known as australopithecines. Their brains were still no larger than those of chimpanzees, and they probably still spent time in the trees, but they were now better adapted to walking upright. The opposable big toe gave way to the modern in-line big toe; the foot was arched; and there were other adaptations to the striding gait of a modern human. The australopithecines are now known to have made stone tools not too dissimilar to those of the first humans. They were widely distributed in Africa, though lumpers and splitters argue over just how many species there were. It is generally accepted that the first humans evolved from australopithecines, though from which species and where remains disputed.

The third and final phase lasted from 2.0 million to around 200,000 years ago, and it was during this period that the first humans emerged. In this work, I use the term human to refer to any hominin belonging to Genus Homo, not just Homo sapiens. When I am referring specifically to the latter, I use the term modern human as a synonym. Just how many human species there have been is a field in which the lumpers and splitters have had a field day, but there are probably at least seven: Homo habilis, Homo erectus, Homo heidelbergensis, Homo neanderthalensis (the Neanderthals), Homo floresiensis (the diminutive hobbit people from the island of Flores), the recently-announced