Photo by NASA, Wikimedia Commons
There are, according to the World Population Clock, 7.4 billion people currently living on Earth. Like most very large numbers it is difficult to really appreciate what a term of this magnitude really means, but we can compare it with some other numbers to try to gain some perspective.
For example, when I was born in 1951 there were 2.5 billion people on Earth. Inference: the Earth’s human population has tripled during my lifetime! LOTS of people have been added to our Earth in the past 60-some years!
Also, if we think about humans living not on the supportive crests of all of our technologies but instead existing as just another species in the Earth’s natural ecosystems (we would be hunters and gathers and scavengers, and, of course, prey for just about any other predator out there!), then the Earth could probably only support about 3 million humans. Inference: if humans were really and truly part of Nature, 99.96% of us who are alive right now would not (and could not) exist!.
All of this, of course, leads me to think about Agriculture!
Photo by J. Atherton, Flickr
I was reading a chapter in John Reader’s book Africa: Biography of the Continent in which he discusses the “invention” of agriculture. According to Reader, the first evidence that humans had learned how to control the growth and productivity of wild plant species comes from a site in the the Klasies River Caves in South Africa that is dated back to about 70,000 years ago. Abundant residues of starchy plant roots have been found on stone tools and relics on this site, and via a long chain of logic and inference researchers have concluded that these early humans controlled and cultivated crops of widely dispersed plants (probably through controlled burning) and augmented their hunter/gatherer lifestyle menu with a rich and predictable source of carbohydrates. This cultivation, though, was interrupted by some unknown set of events, and this first agricultural technology was abandoned. Apparently, this cycle of temporary adoption of plant cultivation followed by a return to the old ways of existence was repeated many times over many millennia by people in Africa and Asia.
Public Domain, Wikimedia Commons
About 12,000 years ago, though, armed with domesticated plants and animals gathered from the Middle East, Anatolia (“Turkey”), and the Nile Valley agriculture took hold and became the primary system by which humans fed themselves. The success of this continually evolving system of controlled food production can be read in the stunning growth of the human population on Earth (data from Goldwijk and van Drecht (2007)): in 10,000 BC there were 2 to 4 million people on Earth, but by 1000 AD there were 295 million people! By 1850 there were 1.26 billion people, by 1951 (already mentioned above) there were 2.5 billion people. Now there are 7.4 billion of us! The exponential nature of this population growth curve is breathtaking and it was fueled in large part by the growth and change in agriculture!
Humans have existed as a species (Homo sapiens) for about 200,000 years. Over 190.000 years of this time span the limits of the natural carrying capacities of the Earth’s ecosystems have kept the number of humans at or often well below the 3 million mark. Agriculture, which celebrates its 12,000 year birthday, oh, let’s say next Tuesday, has allowed our numbers to soar!
The path, though, through our 200,000 years of existence has not been smooth. Geneticists looking at patterns of human DNA infer at least two evolutionary “bottlenecks” (severe population declines) in the history of our species. Li and Durban (2011) describe some of this data in their paper in Nature. One population decline occurred just before or possibly just as the genus Homo came into existence about 3 million years ago. The population of the “humans-to-be” was winnowed down to just 10,000 individuals all packed in to a small area in Africa! Possibly this restriction of the “humans-to-be’s” genome assisted the emergence of the intelligent, and extremely adaptable Homo line of species!
Later, when Homo sapiens began to spread out of Africa into Europe and Asia, the second bottleneck occurred. This was between 20,000 and 40,000 years ago and it involved the number of humans on Earth declining to possibly just 1200 individuals in Europe and Asia and just 5700 individuals in Africa. Again, this bottleneck may be one of the reasons that explain why human beings (all 7.4 billion of us!) are so similar to each other genetically!
All of which gets us to a video made by writers at New Science who posed the question “what if humans didn’t exist?” These two past bottlenecks suggest that this contemplation of a world without us may not be too great of a stretch of the fabric of science!
What if an environmental crisis wiped out Homo sapiens early in our existence as a species? What if the eruption of some immense volcanoes rapidly and radically transformed the climate of the Earth and caused a mass extinction of Late Permian proportions (90% of all species on Earth went extinct)? What if an asteroid crashed into the Earth and vaporized the young savannas of Africa where our incipient species was trying to eke out a living? This asteroid strike might resemble the extraterrestrial impact event of the Late Cretaceous that drove the dinosaurs (among others) into extinction.
What would Earth be like if Homo sapiens were not here?
M. Anton, Wikimedia Commons
There would be no cities, no large herds and flocks of domesticated animals, and no vast fields of managed agricultural ecosystems. There would be oceans full of fish, large herds of large mammals on the extensive temperate and tropical grasslands (along with some equally large predators). Mastodons, giant ground sloths, large toothed cats, not to mention bison would occupy North America and would have to deal with those annoying, sky-filling clouds of passenger pigeons (and more!) in their daily existences.
There would be no rising levels of atmospheric carbon dioxide (because there would have been no Industrial Revolution and no fossil fuel burning binges). There would be no accelerated Greenhouse Effect. Maybe, then, it would time for another Ice Age to start up! (Earth is, in a geological time sense, long overdue for another round of continental glaciers!).
J. Gurche, Wikimedia Commons
But maybe, the evolutionary drive toward intelligence is too strong to be thwarted by just a single extinction. Maybe other species, maybe other Homo species (let’s not forget about the Neanderthals!) would have been favored by the elimination of Homo sapiens. Maybe if left on their own, they would have developed agriculture, and science, and had a space program and maybe even more! Maybe, the folks at New Science speculate, the Earth would look a lot like it does now even if Homo sapiens hadn’t been around to alter it!
I am not sure if that is an optimistic or a pessimistic point of view!
Bill,
I graced this planet with my presence just a year after yourself, and have often used just that same fact of the tripling of the world’s population in my lifetime to spark awareness of the risks to civilization that exponential growth poses. But it never registers: people can’t seem to fathom exponentiation. Linear curves, yes: hockey stick curves, no.
One of my all time favorite quotes from a biologist was “humans are too greedy, too clever and too numerous”.
I was only dimly aware of the two near extinction events that Homo endured. Also interesting was the evidence that agriculture didn’t take hold until 12000 years ago, despite the fact that our species Homo Sapiens Sapiens has existed for over 250000 years.
I recall Elisabeth Colbert, the science writer for the New Yorker, saying at a lecture Jennie and I attended on climate change that agriculture COULDN’T emerge until the planet entered the extraordinary stable climate know as the Holocene-12000 years ago. Looks like we are forcing the atmosphere out of stability and back into states that do not foster continued civilization with populations approaching 9 billion by mid-century.
Just when we must increase food production by 70% according to the UN Food and Agriculture Org. to feed that many people by 2050, we are undermining our ability to do so by not just disrupting the climate, but by pushing every biological system to the wall at the same time. ( Colbert also wrote “The Sixth Extinction”).
So we are watching humanity banging into the walls of our petri dish in our lifetimes, Bill. Nature’s way of resolving the situation will not be pretty and I don’t want to be around to witness it. But you never know, perhaps there is a supernatural way out, we get very lucky, or even we develop a less destructive consciousness in time. Can’t say I’m optimistic!
Robert