Since the discovery in the 19th century of Neanderthal remains, the cause of their extinction has arguably been the most compelling mystery in human evolution. Why did a species that was so like us, wore clothes, used fire, buried their dead, made jewellery and spoke to each other, dwindle in number and disappear from the face of the Earth? Perhaps, subconsciously, our interest in the fate of the Neanderthals is intrinsically linked to questions that we ask about our own existence, and we hope that by understanding their extinction, we may better know ourselves. Whatever the reason, the mystery has captured the imagination of scholars and the public alike. Explanations abound, and run the gamut from those that draw on rigorous scientific research to those inhabiting the more outlandish, albeit occasionally entertaining, fringes of pseudoscience and conspiracy theory (aliens or yetis, anyone?).

Among scientists, theories on the Neanderthals¡¯ disappearance are divided, for the most part, into two main strands. The first suggests that environmental change made survival impossible for the Neanderthals, who were outcompeted by newly arrived groups of African Homo sapiens that pushed them to the margins of the landscape and ultimately extinction. More recently, the advent of Neanderthal genomics has opened up the possibility of disease playing a silent role in the demise of our evolutionary cousins. However, we should remind ourselves that Neanderthal extinction took place over a huge geographical expanse and a time scale of about 20,000 years. In light of this, we should almost certainly be talking about extinction causes ¨C plural rather than singular. In other words, what did for the Croatian Neanderthals may have been completely unrelated to the causes of the demise of the French populations.

Explanations abound, from those that draw on rigorous scientific research to those inhabiting the outlandish fringes of pseudoscience

Anthropologist Pat Shipman¡¯s main research expertise is in taphonomy, the study of how bodies decompose into skeletal and then fossil remains. In recent years, however, her science writing has brought human evolution to a much wider audience than that confined to the groves of academe. I am an admirer of her work; her style is engaging yet authoritative and the pages fly by. The book she co-wrote two decades ago with Alan Walker on the evolution of Homo erectus, The Wisdom of the Bones: In Search of Human Origins, is a popular science classic, and her new book is cast from the same mould. It provides an up-to-date summary of the current thinking about Neanderthal evolution and presents many complex ideas with a great deal of perspicacity and wit. The Invaders offers us the appealing prospect of an expert writing on her specialism and clearly having a great deal of fun doing so.

É«ºÐÖ±²¥

Shipman builds an extremely compelling case for the role of Homo sapiens as an invasive species who arrived in Europe about 40,000 to 50,000 years ago and had an immediate impact on their new ecosystem. The Neanderthals were not the only victims. Using archaeological data, Shipman highlights that once Homo sapiens arrived in Europe, the ¡°carnivore guild¡± (a group of animals including the cave hyena, cave lion and scimitar cats that exploited the same resources in broadly the same way ¨C in this case smaller prey species) began to disappear and finally became extinct. She argues that the Neanderthals, also members of the carnivore guild, shared the same fate as a result of competition from Homo sapiens. So far, this idea is uncontroversial and in line with the thinking of many other scholars who also contend that modern humans out-thought and out-played the indigenous Neanderthals. What makes Shipman¡¯s argument really stand out and offer a fresh perspective on the extinction of Neanderthals is the role that she gives to wolves in the process that led to the dominance of Homo sapiens and the eventual decline of the carnivore guild¡¯s original members.

Unlike the Neanderthals, who never domesticated animals, Shipman says, we formed an alliance with wolves shortly after our arrival in Europe, leading to their eventual domestication, and this lethal combination allowed us to outcompete all other predators. Wolves would track and corner large animal prey that was potentially too big for the pack to risk attacking themselves, before allowing humans to move in for the kill using spears and other projectile weapons. In this way, both species used their key skills to form a symbiotic super-hunter. Furthermore, this type of teamwork would have allowed the human-wolf partnership to scare away would-be meat thieves such as cave lions and hyenas, and of course other wolves.

É«ºÐÖ±²¥

Of course, this theory would be merely speculation were it not for the supporting evidence that has only recently come to light. Traditionally, the domestication of dogs had been coupled with the development of agriculture about 10,000 years ago, even though genetic research had started to push this date back further. However, in a perfect example of new data brushing aside old ideas, recent radiocarbon dating of dog fossils from Belgium indicates that they are 36,000 years old. Not only is this considerably earlier than previously believed, but it also falls squarely within the time frame that Shipman suggests for the forging of the alliance between humans and wolves. She comments: ¡°This is just the sort of discovery I personally like best. The methodology is sound, the comparative sample sizes respectable, and the result makes you rethink a lot of what you thought you knew.¡±

It is difficult to argue with this sentiment, and it¡¯s extremely refreshing to see a fellow researcher identify not only why a result is good ¨C although we do tend to be fondest of the ones that support our ideas, of course ¨C but also to heap praise on the method, sample selection and outcome of research. Inevitably the thesis is not flawless (lest we forget, even Charles Darwin¡¯s On the Origin of Species had some errors), and Shipman is the first to note that there are gaps in her theory. One is left with a sneaking suspicion that the subtitle of this book owes more to an editor with an eye on sales than anything else. Some of Shipman¡¯s peers will likely point to research that offers contrary data or different interpretations, but this is unavoidable. Indeed, one of the great strengths of human evolutionary science is how new evidence continues to oblige us to re-evaluate our relationship with extinct hominid species, and Shipman is quick to sound a note of caution that ideas that find backing from today¡¯s evidence may be swept away by developments in the field tomorrow. Genetics is arguably the area of study where this is most often true. A quick glance at the past 15 years of research into Neanderthal genetics shows the consensus moving from the view that there had been no interbreeding with Homo sapiens to arguments for multiple interbreeding events within a relatively short span of time.

There will doubtless be readers who disagree with Shipman¡¯s theory and, after all, an unsolved mystery is much more fun than a solution. But the greatest strength of The Invaders lies in its approach to science and the palpable delight that Shipman takes in simply thinking. Remember thinking? Not publishing for the sake of it, not worrying about impact or research excellence framework returns, but taking time to examine data, to consider the big questions and to synthesise across multiple subjects to produce a viable and intellectually satisfying theory.