Land and Limits Book

This classic of biogeography has been on my to-read list for a few years (I'm not sure where I got the rec from - possibly Against the Grain: How Agriculture Has Hijacked Civilization?). I was under the impression it was a narrower and less fully formed iteration of Jared Diamond's ideas in Guns, Germs, and Steel: The Fates of Human Societies. There is a lot of overlap between the two, especially in the epidemiological arena (really an older idea than either of them, and Crosby goes so far as to name it "William Hardy McNeill's Law"), but Crosby has a fresh authorial voice, a subtly different question, and compellingly different answers.

While Diamond is interested in explaining a political and economic reality (disparity of "cargo" possession) using geographic factors, Crosby asks an ecological question: why did Europeans end up multiplying and displacing the native inhabitants in a few other continents and not others? The questions aren't that different, since the process of colonization was also the process of rapidly obtaining massive wealth. It is imaginable that one could occur without the other, however: siphoning resources out of productive colonies like India, Mexico, and the Congo without substantially replacing their populations. Asking the question with a different frame gave Crosby answers that felt new to me after taking Diamond's ideas for granted for ages.

Crosby interestingly insists on describing the "Columbian Exchange" with his "seams of Pangaea" concept. These seams - the rifting lines which have by geologic definition not been crossed during the dispersal of Gondwana and Laurasia's bits - are the only new lines that European explorers traversed; the addition of India to the Asian continent and the land bridge between the Americas both united chunks of disparate Gondwana and Laurasia, with all the consequences that entailed for their biota. In spite of these mix-ups in geologic time, the evolutionary relevance of the concept remains: each separate continent had stabilized a unique set of ecosystems by the Pleistocene.

In that vein, Crosby metaphorizes the indigenous colonization of Australiasia and the Americas as the "shock troops" of the later European invasion. This is an ecologically interesting argument because the Pleistocene extinction event eliminated many of the more fantastic organisms that differentiated the Neo-Europes from the Old World, and thus swept away a major source of competition (which proved problematic in, eg South Africa). Fortunately, he doesn't push it too far past its usefulness (after all, he still needs to explain why the main front did so much harm to these indigenous shock troops).

I don't mean to spoil it for you, but Crosby's main thesis is that the European expansion to the "Neo-Europes" was successful and one-way because the early and widespread emergence of agriculture there created a whole codependent biota adapted to disturbance, from fire, grazing, and the plow. When this biota was introduced into the stable climax ecosystems of the New World, it succeeded because it created a leap-frogging wave of disturbance and weed colonization. Disease organisms caused catastrophic population crashes in the most prominent ecosystem engineer, humans, leaving an ecosystem in flux. Livestock destroyed herbs that hadn't seen a grazer since the Pliocene. Colonists lit fires and logged extensively, opening new pasture and farm land to support their weeds. Without European weeds, all this change could have resulted in catastrophic soil erosion; weeds covered the bare ground and did damage control for human mismanagement. All this happened in relative absence of the pests and diseases and competition that limited growth at home (while the disease load was disastrously high for natives, sparse populations and good nutrition made the colonies vastly more healthy for colonists then Europe).

Crosby's ultimate answer is that civilization was aided in its conquest of the Neo-europes by a biota adapted to civilization's own rather severe mode of environmental modification. Few neo-european organisms went the other way because the environment in the Old World was simply too harsh for them. The disease issue is partially a consequence of the Old World's high population densities, poor sanitation, and contact with a broad array of livestock. It is also sort of a distinct issue, a consequence of separation, long exoduses and changes of climate that shook off the disease organisms and left Native Americans and the Maori living in a near-paradise where plague was nearly unknown.

Unlike Diamond, Crosby never really addresses why Europe was the portion of the Old World that crossed the seams of Pangaea and not India, Ethiopia, Nigeria, or China. He also fails to explore the implications of his explanation even to the extent I portrayed it above (perhaps I'm reading too much into it?).

In the first part of the book, Crosby's prose seems full of pithy and sharp phrases, like "The Crusader states died like bowls of cut flowers," which makes it fun to read. This kind of trails off into the later parts of the book, though, and the narratives become a bit dull. In general, a lot of the information presented seems a bit gratuitous, demonstrating the plausibility of his points rather than proving the validity of his arguments. This makes the book feel loose and superfluous in parts. The conclusion really peters out: just as he's getting to the interesting bits, he seems to lose focus and drive. The long-awaited revelation of Chapter 11 kind of dribbles out in a disorganized slew.

Despite all those flaws, Crosby does raise a lot of interesting points, and he treats weeds, livestock, and disturbance as forces that shift ecosystem dynamics (which is interesting and seems crucial) more closely than any other author I've met. He seems a bit ahead of his time in that respect (a lot of the ideas from The Work of Nature: How The Diversity Of Life Sustains Us, a much more recent book, feel like they could be valuably applied to an update of Crosby's work), so perhaps he should be forgiven for the amount of hand-waving that comes in when he discusses what consequences the spread of weeds and bovids actually had.