The predominance of humans and their evolutionary predecessors goes back almost two million years. Further into the distant past, our ancestors were just like any other of the players on the African landscape. In terms of lifestyle, they were not much different from the baboons of today – they were more often the prey than the predator, and were just another cog in the machinery of life.

Back then, it is not unreasonable to estimate, there were probably around 200,000 of our ancestors populating Africa. This figure is based on numbers of similar species, such as baboons. Keep that number in your head for a few paragraphs.

Mammalian decline

By 1.8 million years ago, our ancestral population – and its impact – clearly grew. The wake of our growth was first felt in Africa, where large mammals started going extinct at an unusually high rate. This was no mere coincidence, for as our population spread from Africa, the mammalian extinction rates inevitably rose on other continents as well. We were a success. We out-competed some animals, and hunted others to their demise.

Starting some 10,000 years ago – our ancestors now full-fledged Homo sapiens – mammalian biodiversity hit an unprecedented rate of decline. What happened? Quite simply this: agriculture.

By its very nature, agriculture normally has to reduce biodiversity. It replaces rich and productive ecosystems with just a few life forms meant primarily for human consumption. No longer was it a matter of hunting mammals to extinction – we just simply denied animals, and plants, the resources they needed, and they quietly went away. Some forever.

Mass extinction

Today the situation worsens. Despite noble attempts at conservation, human beings are rapidly leading the planet to a mass extinction of life forms that may rival the losses of 65 million years ago that took the lives of most dinosaurs. As our population grows by over 200,000 people per day – there is that number again – we take over more and more of the landscape. Plants, animals, even microbes, get pushed aside.

But if we lived more responsibly would our impact be less? I’ll give a qualified “yes.” Of course it would. And before I go on to the controversial part of what I have to say, let me go on record as clearly supporting conservation measures of all kinds. But here is where I get in trouble with the conventional wisdom. In my recent book, Sparing Nature, I proclaim: “The greatest and most effective conservation measure to save earth’s biodiversity is to halt the growth of the human population, and perhaps reduce our numbers.”

Whereas few scientists would disagree that population is an important consideration, others think that our gluttonous behavior is the root cause of biodiversity loss. But recently I’ve shown, in research published in the journal Biological Conservation, that there is a very strong correlation, country by country, between human population density and biodiversity threats. In a forthcoming paper, in American Journal of Physical Anthropology, I add that per capita Gross National Product – a measure of affluence – does not correlate with biodiversity threats across nations.

Baboon troops

Does this mean we are free to rampantly consume resources as long as we keep our numbers down? Absolutely not. It means that the effects of our large populations on biodiversity are mediated in different ways, in countries rich and poor. It means that if we don’t quell the growth of our human population, and do so soon, that all conservation efforts will be for naught.

Think of it this way. Could the world sustain a growing population of over 6 billion baboons? Probably not. Right now, in Africa, baboon troops are culled on a regular basis. They are too successful at breeding, and raid crops that were supposedly meant for humans. They are voracious consumers. If they had a large brain – which is a metabolically expensive organ to maintain – they would consume even more. They would have to. So do we.

I noted in an earlier book, The Riddled Chain, that baboons aren’t the only animal culled. “How ironic that even with declining numbers of elephants in Africa, we are willing to cull them in some areas to prevent the environmental degradation that results from their population growth. But so many among the most environmentally destructive species of all, Homo sapiens, are unwilling to curb our own population growth in a responsible manner.”

I don’t want to fathom culling humans. It would be easier to show some reproductive restraint. As I’ve said many times: “It’s easy to do something about the number of babies born – we know what causes them.” And dealing with the cause will be a whole lot less difficult than managing a planet that is bereft of the biodiversity that sustains it.

We are the species at the top, and now we must take responsibility. That would be to the credit of future generations, not only or our species, but of those on which we depend.

Sparing Nature: The Conflict between Human Population Growth and Earth's Biodiversity, was published in 2003 by Rutgers University at $28 or £16.85.

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