Human Biogeography

10. We Affect Other Species’ Biogeography

225 10 We Affect Other Species’ Biogeography It is clear, therefore, that we are now in an altogether exceptional period of the earth’s history. We live in a zoologically impoverished world, from which all the hugest, and fiercest, and strangest forms have recently disappeared. [803, Wallace, 1876, p. 150] An adequate knowledge of the fauna and flora of the whole world . . . can never now be obtained, owing to the reckless destruction of forests, and with them of countless species of plants and animals. [805, Wallace, 1880, p. 7] summary Ever since modern humans first spread out of Africa, and probably before then, we have changed the range of other species, irretrievably altering the globe’s biogeographical patterns. In a variety of ways, we have driven thousands of species to extinction , or in other words, reduced their geographic range to zero. Our movement across the globe can often be mapped by the accompanying wave of extinctions. We entered northern Europe and the Americas at a time of rapid, massive change of climate, and probably hastened extinctions initiated by the climate change there. Elsewhere, we were the original and main cause of extinctions. But several species have benefited from our presence, greatly extending their range as a result of their association with us. Our parasites and crops are the obvious examples. An often-assumed characteristic of successful dispersing species—weed species—is that they are not necessarily good competitors [766]. H. sapiens is clearly an exception to that generalization. Humans are both good dispersers and good competitors. As we have spread across the world, we have driven, and continue to drive, many species to extinction, 226 | Interaction among Cultures and Species possibly including species of our own genus Homo. If we want to stop that extermination, it will be helpful to understand the biogeography of the extermination and its causes, as well as of the occasional extension of species’ geographic ranges that we have allowed or encouraged [828]. HUMANS VS. OTHER HOMO SPECIES As modern humans spread out of Africa from roughly 55 kya, they moved into regions occupied by Homo erectus, which was still inhabiting Java up to maybe 30 kya [748]. The humans certainly also met Neanderthals , extant in the refugium of southern Spain up to 28 kya, maybe even 24 kya, if gone from the rest of Europe by about 30 kya [220, ch. 7; 223]. We know that the two species met because Neanderthal genes are in the human genome [288], as is the case for the Denisova Homo, extant in southern Siberia up to at least 40 kya [431; 637]. Erectus had disappeared from the Asian mainland so long before the arrival of modern humans, over 200,000 years beforehand [748], that we cannot be blamed for the majority of the decline of Erectus. Nevertheless , the latest dates for Erectus, Neanderthal, and Denisova coincide with dates for the spread of modern humans outside of Africa. So, did modern humans cause or hasten the extinction of any of these other Homo species? Or was the rapidly cooling climate of the northern hemisphere as humans dispersed out of Africa responsible for the disappearance of the final populations of Erectus, Denisova, and Neanderthal? The short answer is that we do not know. Evidence against direct competition between modern humans and Neanderthals used to be the fact that nobody had found a site containing contemporaneous Neanderthal and modern human remains [220, ch. 7; 699; 700]. However, if evidence and argument that modern humans contain Neanderthal genes [288] is upheld, then clearly the two species must have met, and equally clearly, the possibility of competitive exclusion must be retained. If our ancestors 30 kya were anything like us in the last few centuries, any competition could well have been active contest, with the losers being eaten [485]. Alternatively or as well, if the modern humans were more efficient hunters and gatherers, they could have depleted the game populations sufficiently or made them so fearful that Neanderthals could no longer find sufficient food for survival [250]. The supposition that the humans were more efficient food gatherers than Neanderthals, because of better tools, is speculation. But it seems We Affect Other Species’ Biogeography | 227 likely, given that we survived and Neanderthals did not.a Also, a Neanderthal could well have needed more energy in hunting than a similarsized modern human, because of the Neanderthal’s inefficient locomotion (chapter 5). [425, ch...