2nd Street

Here in the 21st century, humans are urban animals. Most of us live in cities, and the total urban population grows constantly, at the expense of rural areas [1]. This change is occurring worldwide—in North America, Asia, Europe, and across the southern hemisphere. 


One question worth asking is—how did we get here? Our distant ancestors are tree shrews—small, insectivore-like forest inhabitants [2]. Our closest ancestors are chimpanzees, jungle-dwelling, arboreal vegetarians with an occasional taste for a serious meal of meat. And here we are now, inhabiting densely packed cities about as far removed from jungle habitat as it is possible to get.


The evolutionary and cultural journey from the forests and savannahs of Africa to the megacities around the world today took time. But we became village dwellers early in our history, and it was just a few technological revolutions from there to the skyscraper. Well, maybe more than a few. 


The story involves three species in the genus Homo [5]. Homo erectus was possibly our immediate ancestor, walking upright on the African landscape nearly two million years ago. With large bodies and brains, erectus needed an energy-rich diet. Their family groups ate a high proportion of meat in addition to fruits and tubers gathered from wild plants. Lacking the claws, jaws, teeth, and strength of predators like saber-tooth cats and dire wolves, erectus had to innovate to capture, kill, and butcher animals. Homo erectus fossils are associated with some of the earliest stone tools, mostly sharp-edged multipurpose knives that might also have served as axe or spear heads. Fire was also a tool first associated with H. erectus. Fires were not only used for cooking meat (increasing its suitability as a food source), but were also social centers where conversation and other social interactions took place [6].  


With stone tools and fire at their service, clans of Homo erectus weren’t tied to the ancestral African plains. In travels that would be mirrored later by our own species, they emerged from Africa, establishing populations in Europe, the Middle East and parts of Asia. Maybe we needed the evolutionary practice to perfect the trick of global occupation.


Next up was Homo neanderthalensis [9]. They moved out of Africa and expanded across Europe and into the north, and made it as far as Siberia [8].  Neanderthalensis was a quintessential hunter, but also a gatherer. They lived in family groups, and were often sedentary in favorable habitats—thus their fame as “cave men”. Apparently not stupid, when they found good conditions, they stayed put. Evidence from sites dated 125,000 to 250,000 years ago in France suggests their diet included, in addition to large game animals, birds, fish and starchy vegetables [7]. Perhaps they sometimes migrated seasonally, and used certain sites annually on circuits following game or ripening food plants. The last Neanderthals lived in long-inhabited sites in the Mediterranean or the subarctic between about 35,000 and 28,000 years ago, depending on evidence yet-to-come [12].


A sedentary habit is the first step on the road to agriculture and true villages. But first came Homo sapiens Artemis, the hunter.


Between about 150,000 and 50,000 years ago, a few species (of a community of many species) of large land mammals went extinct in Africa and tropical Asia. Followed closely—between 50,000 and 10,000 years ago—by a large proportion of the large mammal species in North and South America and Australia. Between about 5,000 and 200 years ago, large animal species disappeared on Madagascar, New Zealand, and Pacific islands [13]. This pattern coincides precisely with the appearance of Homo sapiens in these regions. Likely the faunas of Africa and Asia suffered relatively few extinctions because modern humans evolved in and inhabited these areas side-by-side with the large mammals for most of our time. The mammals had time to adapt, to learn how not to be killed in massive numbers by hunting humans. 


Then people appeared rather suddenly and in large numbers in northwestern North America. South of the ice sheets were prairies, densely populated by large mammals including various kinds of horses, cattle, camels, rhinos, elephants, antelope, deer, glyptodonts (large, armored armadillo-like animals), cats, rodents and sloths. Similar, perhaps greater, diversity characterized South America. 


Within a few thousand years, as the climate warmed and people spread out geographically, much had gone wrong. Unused to human hunters, horses, rhinos, and elephants were gone completely, only a few species of antelope, cattle (bison, musk ox), camels (such as llama, alpaca and vicuna), big cats and deer remained. Of the rest, some survived as smaller remnants of their former glory—armadilloes, sloths, rodents. 


The pattern was repeated when people made it to Australia and Madagascar, and subsequently to New Zealand and Pacific Oceania. Modern human beings were formidable hunters, stalking the landscape for big game taking full advantage when they found it [14].


But humanity was not destined to live out its days in itinerant hunting. 




Notes


[1]


[2] There is some technical debate about this. The issues are laid out in a web portal of uncertain provenance, but well-referenced, at http://www.theprimata.com/tree_shrews.html


[3] A detailed dietary audit of chimpanzees, presented at a colloquium of the International Congress of Anthropological and Ethnological Sciences by faculty from the Department of Anthropology of Harvard University is available at 
http://cast.uark.edu/local/icaes/conferences/wburg/posters/nconklin/conklin.html


[4] Living things are classified in a system pioneered by Carl Linnaeus, a Swedish scientist in the 1700s. The “Linnaean System” retains the original Latin, and every species on earth is identified by a unique two-word name (the system is also called “binary nomenclature”), first the Genus, capitalized, which represents recognizably different species, lower case, the very organism under consideration. These names change as specialists debate relationships among animals and plants. The domestic dog is in the genus Canis, indicating its ancestry in the wolf clan, and usually the species familiaris, meaning familiar to us humans. Recently there has been a movement to link the domestic dog even closer to the wolf, as Canis lupus (species name for the gray wolf) in a subspecies, or variety, Canis lupus familiaris. Either way it’s the same animal, with a genome very similar to that of the wolf. The scientists may or may not sort it out to their satisfaction, for our purposes it’s enough to know that it’s our dog, companion animal recently evolved from the wild wolf. 


[5] The Smithsonian Institution provides an excellent and generally up-to-date and authoritative discussion of human ancestry at the web portal
http://humanorigins.si.edu/research


[6] http://humanorigins.si.edu/evidence/human-fossils/species/homo-erectus


[7] Hardy BL, Moncel M-H (2011) Neanderthal Use of Fish, Mammals, Birds, Starchy Plants and Wood 125-250,000 Years Ago. PLoS ONE 6(8): e23768. doi:10.1371/journal.pone.0023768


[8] Range maps of various provenance are available at http://news.nationalgeographic.com/news/2003/03/photogalleries/neanderthal/
and http://www.springerimages.com/Images/LifeSciences/1-10.1007_978-3-540-33761-4_56-1


[9] Some authors place neanderthalensis taxonomically as a subspecies of our own species, Homo sapiens neanderthalensis. This approach has credibility because of growing genetic evidence that sapiens and neanderthalensis interbred. Ability to interbreed is a common definition of a species. 


[10] 


[11]


[12] John Roach reported on evidence for the younger date on the Iberian Peninsula in National Geographic News on 13 September 2006, and on evidence for the older date in subarctic Russia on 13 May 2011. Both dates are subject to anthropological debate and additional finds are needed to sort things out.


[13] The history of large-mammal extinctions and the likely role of modern man in same is well presented and documented in Martin, P.S. 2005 Twilight of the Mammoths: Ice Age Extinctions and the Rewilding of North America. University of California Press, Berkeley. 


[14] The vision of modern human hunters as primary agents of extinction of large mammal faunas is not shared universally. Many anthropologists, sociologists, and some ecologists, find the assumption that pre-industrial humans could imbalance the ecosystem to that degree to be very unpalatable. A more benign view of the matter may be found in Delcourt, P.A. and H.R. Delcourt 2004. Prehistoric Native Americans and Ecological Change: Human Ecosystems in North America since the Pleistocene. Cambridge University Press, Cambridge, UK.