Are humans extinction-proof?

June 9, 2011 By Darren Curnoe
Are humans extinction-proof?
Darren Curnoe

Does climate change seriously threaten to wipe out the human species if left unchecked? Examining our evolutionary past suggests it might once have been the perfect catalyst for our extinction. But now?

On January 14 of this year, the Bulletin of the Atomic Scientists moved the hands of its Doomsday Clock one minute further from midnight (it’s now six minutes to midnight), encouraged, it was announced, by the “progress seen around globe in both key threat areas: nuclear weapons and ”.

First published in 1947, the bulletin was founded by scientists, engineers and other experts involved in the Manhattan Project. The clock continues to serve as a metaphorical countdown to the apocalypse – the annihilation of humanity – set for midnight.

Today, the bulletin’s Board of Sponsors, comprising no less than 18 Nobel Laureates, almost every one of them a physicist or chemist, sets the hands of the clock based on their reading of “threats to the survival and development of humanity from nuclear weapons, climate change, and emerging technologies in the life sciences”.

They’ve a much wider brief now, a longer list of threats, and, I guess, more reasons to be pessimistic.

Around 500 million years ago, animal life was almost non-existent on Earth. Today, biologists recognise up to 6 million animal species.

Humanity – Homo sapiens – is just one among the 4,500 living mammal species; and some understanding of where we might be headed can be gleaned from where we’ve been – our evolutionary journey.

Our starting point as a group of two-footed, small-toothed, weakly-muscled, brainy “have-a-chat” apes is the ancestor we share with living chimpanzees some 7 million years ago.

(The two chimpanzee species are endangered, incidentally, because of the environmental destruction caused by us, their closest cousin).

Our evolutionary group – the hominins – diversified quickly after the split from the human-chimp ancestor, and through its multiple evolutionary iterations natural selection produced 25 or 30 two-footed ape species – undoubtedly with more to be found as anthropologists discover more fossils. All of these are now extinct, except us.

Those 7 million years represent only the last couple of minutes on a 24-hour clock of Earth’s 5 billion year history. The culling of 30 species to 1 in this short timeframe, or a more than 95% loss of hominin biodiversity, is worse than the worst mass extinction episode recorded in the fossil record: the Permian event some 250 million years ago.

But these mass events obscure the fact that, in the history of life, extinction has been a dominant theme, a continuous process. Evidence from the last 600 million years shows roughly one-third of existing animal species going extinct every 10 million years.

Seen in this context, the rate of extinction in the human evolutionary tree is striking, about three times faster than normal. This strongly suggests that we hominins are a highly extinction-prone mammal.

Why the dramatic loss of hominin diversity? What caused all these species to disappear? These are difficult and complex questions, but the answer may in part centre on the dramatic changes in climate that provided the backdrop for much of our evolution.

The last half million years or so in particular represent an episode of especially severe climate fluctuation, with intensely cold periods followed by warm phases, flip-flopping between the two on timescales of hundreds or thousands of years – in short, the worst bit of the 2.6 million-year Ice Age or Pleistocene Epoch.

The archaeological record of Europe suggests that vast areas were largely emptied of hominins during cold phases only to be recolonised during warm periods.

Hominins, pre-dating our own species, were living in Europe at latitudes as high as 53° north by 700,000 years ago.

The 53rd parallel runs from the United Kingdom east through the Netherlands, Germany, Poland, Belarus, Russia, Kazakhstan, China (Inner Mongolia), United States (Alaska), Canada and Ireland.

Many places at this latitude today experience temperatures as low as -40° Celsius. But the climate at that time was Mediterranean in character. Soon after, the planet plunged into another cold phase lasting 100,000 years, with vast areas of Europe covered by ice.

Biologists have identified various intrinsic features of mammal species that increase their chances of extinction. They include traits such as:

• large body size;
• narrow ecological breadth (i.e. specialist feeders);
• low abundance, or sparse numbers of individuals, in the landscape as well as fluctuation in population over time.

Hominins are large mammals. Estimates of mass and stature for many Ice Age species would easily qualify them for spots on the front row of a rugby team … and that’s just the females!

Large mammals are slow to mature and reproduce, and normally have one offspring at a time. While many extinct hominins were, like our own species, omnivorous, those living in cold climates relied heavily on animal food, as have recent hunter-gatherers such as the Inuit. This represents a narrowing of dietary niche on a par with many carnivores.

Estimates of population size from this period are remarkably low, with perhaps only 5,000 individuals in warm phases, plummeting to 1,000 or less during the cold stages, probably for the whole of Europe.

If around today, these individuals would be part of an endangered species, vulnerable to rapid extinction. And all of this applied to our own species as well for all but the last little bit of our brief evolutionary history.

Around 10,000 years ago, something unprecedented occurred that altered the course of our evolution: we invented farming. This massive change in dietary, social and economic behavior, a cultural shift known as the Neolithic Revolution, shaped the future course of our own, and the planet’s, evolution in remarkable and unpredictable ways.

It resulted in anatomical, physiological and genetic changes that massively altered our evolution.

Our domestication of plants and animals, and the large-scale clearing of land, altered the history of many others as well. It paved the way for a rise in infectious disease, and social changes such as occupational specialisation, writing, standing armies and empires, long distance trade, money and markets.

But the most profound shift of all was an explosion in human population, the result of greatly improved food security resulting in a dramatic lowering of infant and childhood mortality.

In Europe, from a base of perhaps only 5,000 Ice Age hunter-gatherers, the take-up of farming from approximately 8,000 years ago sharply increased population growth to an estimated rate of 3% per annum, from a long-term average of zero.

This is roughly three times today’s global annual growth rate. From a population of less than 100,000 people worldwide, we have grown in less than 10,000 years to almost 7 billion.

Seen in its broadest context, the history of life on Earth soberly demonstrates that the vast majority of organisms that ever lived, perhaps 99% of them, no longer do. It also shows that mammal species normally last 1-2 before inevitably bumps them off.

Yet, unlike most mammals, including our dozens of extinct hominin cousins, we have escaped the vulnerabilities of a small and massively fluctuating population.

The simple, but profound act, of growing our own food delivered us the food security that ensured most of our children survived and our population grew.

In effect, farming gave our level assurance that the biological isn’t always inevitable. The odds have shifted to such a degree that we may now be, with or without climate change, extinction-proof.

Explore further: Has the Earth's sixth mass extinction already arrived?

More information: This article was originally published by The Conversation.

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3.1 / 5 (7) Jun 09, 2011
I don't think climate change will kill us off, I'm certain it will make life impossible for some, and incredibly difficult for most.
4.1 / 5 (9) Jun 09, 2011
..until that giant asteroid impact, sure, why not?
4.3 / 5 (9) Jun 09, 2011
Hell, even in the event of a giant asteroid hits and its total nuclear winter, there are too many of us, and too many of us with bomb shelters. The death toll might be billions, but people will live. We can filter our own air, and protect ourselves from radiation, what other species can do that?
4.2 / 5 (5) Jun 09, 2011
Never say never, although it certainly seems as though we might be extinction proof, if it does happen there will be nobody left to say I told u so.
4.3 / 5 (11) Jun 09, 2011
We're about as extinction-proof as a species confined to a single planet is likely to be. It would take a near sterilization event to wipe out humanity given the resources we can now bring to bear. Still, surviving is a long way off from thriving.
2.3 / 5 (9) Jun 09, 2011
Nothing is extinction proof.
2 / 5 (8) Jun 09, 2011
Actually, I could be wrong. There are so many Humans, there'd always be plenty of survivors, depending on the event. Even a lot of bacteria (and other micro-organisms) could be classified as extinction proof.
4.4 / 5 (5) Jun 09, 2011
A million years is practically forever in our personal experience. If we survive the next thousand years without a catastrophic setback, we will have likely sealed the deal.
not rated yet Jun 10, 2011
Massive GRB from nearby neutron star can kill all of us before we can realize it.

Detection of GRB is very very very very very very very difficult (at-least from our current technological standpoint).

There are many ways humans can die similar way, massive volcanic activity, sucked by rough blackhole, super or hyper-nova in near by star etc.

Even there could be other unknown ways of dying : slowly degenerative DNA telomere or Y chromosome , or some quantum calamity
5 / 5 (2) Jun 10, 2011
It would take a near sterilization event to wipe out humanity given the resources we can now bring to bear

A supernova in our neighborhood (closer than 100 light years) might do the trick. Not much we could do against that.

Or if we just happen to be aligned with the jet from a pulsar/quasar/black for any significant length of time.
not rated yet Jun 10, 2011
Extinction proof I guess is a good thing. Catastrophe proof we are not. There are a lot of scenarios with gigadeath results that have been postulated lately so it is good to know that humanity at least will regenerate from very small survivor groups. I hope this does not have to happen too many times before we learn how to value,nurture and protect this planet rather than just to exploit it.
not rated yet Jun 10, 2011
A million years is practically forever in our personal experience. If we survive the next thousand years without a catastrophic setback, we will have likely sealed the deal.

Every extinct species had its next few thousand years.
5 / 5 (1) Jun 10, 2011
I think we're extinction proof relative to MOST of what this planet can throw at us, however, as long as we're confined to this one chunk of rock (and for that matter, quadrant of space, really), all bets are off. There are too many things we can do to each other, and that the universe at large could throw at us, for us to be safe. Total nuclear war would kill off a good percentage of the species - I'm thinking upwards of 80% within the first 10 years from the primary attacks and subsequent food and resource shortages, followed by radiation-induced genetic defects that make re-population, short of some miracle mutation, unlikely. Also, any spacial (space-based) phenomenon strong enough to sterilize or completely destroy Earth would also most likely effect any other man made or modified habitat in the solar system, either directly, or indirectly through gravitational effect i.e.large black hole, huge asteroid, Planet-X[insert small snicker here] etc.
1 / 5 (2) Jun 11, 2011
Immortals don't have these issues.

Immortal language - what do they discuss? - What do they ask?
What is mortality? What is Life? What is Dealth?
Actually their prose is like our prose.
1 / 5 (4) Jun 11, 2011
I think we have more to fear from the ideologues, capitalists, and academia promoting the GW AlGoreithm for population control, one world government, social justice, redistribution of wealth, tax incentives and research funding, then from the GW hoax. More people die from cold then from heat.

Atmospheric Carbon Dioxide was likely 18 times todays concentration during the Cambrian period when lifes diversity was at its greatest expansion.
1 / 5 (5) Jun 11, 2011
I think we have more to fear from the ideologues, capitalists, and academia promoting the GW AlGoreithm for population control, one world government, social justice, redistribution of wealth, tax incentives and research funding, then from the GW hoax. More people die from cold then from heat. Atmospheric Carbon Dioxide was likely 18 times todays concentration during the Cambrian period when lifes diversity was at its greatest expansion.
2.1 / 5 (7) Jun 12, 2011
Are we extinction proof? Only a religious nut could even come up with an idea like this.

As a species we do everything we can the opposite of what science tells us promotes species survival. Most notably isolated pockets and overpopulation. We are busily trying to put every person on the planet in a single intermingling group while increasing the population well beyond long term survival limits. We are suicidal as a group, like the proverbial Lemming.
5 / 5 (1) Jun 14, 2011
Extinction probably isn't the right word. There are very, very few events that could wipe out humanity before we get a plan B set up in other parts of the Solar System or eventually on exo-planets. A large asteroid strike being one of them; getting flung out of the Solar System by a wandering neutron star or gas giant is another. But does anyone here really belive that humans will still be around in their current form in, say, a million years?

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