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Managing growth

Tuesday 10 August 2010

Global population remains one of the most pressing issues for future sustainability. Our Future Planet examines where we are now and where we are heading.

Photo Credit: Bies

What is the situation with global fertility? What about enforced rules on child bearing couples? What about enforced sterilisation? Are these ever likely to become necessary? Or will planetary forces themselves halt population increases?

All of these questions are among the toughest the global community has to answer. They impact upon perhaps the most natural of our responses; the urge to reproduce. Population adaptation to better respond to a changing environment remains an evolutionary response, but we may have passed this point. How can we mitigate the vast pressures we’re imposing on the planet that nurtures us?

It’s essential that we do. There’s a simple balance between resources and the populations they can support. When the tipping point is reached, things might potentially go wrong very quickly. Having said that, there are examples in the natural world of ways animals can adapt and evolve to changing situations. Maybe humans could too…

‘In as little as three years, stickleback fish developed tolerance for water temperature 2.5 degrees Celsius lower than their ancestors,’ explains the University of British Columbia, describing a study showing evidence that evolution may help populations survive effects of climate change.

Perhaps similar adaptation techniques might allow us to deal with rising temperatures and our increasing populations. Rowan Barrett from the UBC Department of Zoology led the work. Does he think humans could adapt to changing environments or resources as fast?

“It depends on a number of factors, including the amount of genetic variation present in the relevant trait, the strength of selection acting on the trait, and how heritable the trait is. There are a number of examples of contemporary human evolution, e.g. the spread of lactose tolerance with pastoralism.”

Building tolerance

Maybe if it’s possible for us to learn to tolerate lactose, we might learn to tolerate other food sources making larger populations more viable.

“In addition, the number of generations that freshwater stickleback have been trapped in freshwater habitats since the last ice age, 10,000 years ago, which is 10,000 stickleback generations, is approximately the same number of generations since humans migrated out of Africa,” says Barrett.

“This means the many morphological and physiological adaptations that make freshwater stickleback distinct from their marine ancestors have evolved at about the same rate as the many adaptations that different human populations have evolved for dealing with environmental conditions different from Africa.”

There are of course other ways of controlling populations, but history has taught us such extreme measures like sterilisation programmes or cultural change really shouldn’t come into the equation.

“Oh dear. Certainly not sterilisation programs,” says Barrett. “Humans have used evolutionary biology as an excuse to impose ‘survival of the fittest’ and eugenics policies in the past with terrible consequences.

“A society that lived by evolutionary principles would be a horrible place. That said, I do believe that education can play an important role in limiting rampant population growth. Well informed family planning and birth control could do a lot of good.”

In truth, there’s uncertainty over whether it’s even possible to control or adapt human population growth at all, as it’s never previously been necessary on a global scale.

“Again, I believe that well informed family planning and birth control could help control population growth. Uninformed approaches that have been proven to be ineffective, such as promotion of abstinence, should be stopped. Similarly, the irrational prohibition on condom use by certain religious groups should also be prevented.”

And there are other alternatives. “In the face of changing environmental conditions, a natural population has three choices: 1. adapt, 2. migrate, or 3. go extinct. I don't think many humans would be happy with options 2 or 3. That said, the world could support much larger population sizes if humans did a better job of managing our resources.

“In many cases it is not the number of humans that are the problem, but the way that some humans exploit the natural world. In this respect, it is not the rapid growth in the developing world that is causing damage, but rather the rapid consumption in the developed world.

“More people switching to vegetarianism, flying less, driving less, etc. will be essential if the world is going to be able to support greater and greater numbers of humans. In this regard, it is the increasing consumer demands of China that worry me the most.”

It’s not something we may want to consider, but what does Barrett reckon is likely to happen if we fail to halt population growth?

“This is not really my area of expertise, but if the increasing population growth is accompanied by concomitant increases in resource use, I think we're going to do irreparable damage to the world's ecosystems. Loss of biodiversity and resulting ecosystem functioning could be catastrophic.”

And if ecosystems do begin to malfunction, it’s a certainty that we are likely to see some serious problems developing. But, there is opinion that fertility rates and populations might not be so disastrous as we might think.

Alok Jha, writing in The Guardian, suggests; ‘The global population replacement level, the number of births required to keep population stable, is 2.3 babies per couple. But thanks to increased access to contraception and improving education for women, actual birth rates have been dropping around the world. In the 1950s, it was between five and six; by 2008 it was 2.6. At the current rate, the world's fertility rate will be below replacement level soon after 2020.’

Of course, it’s also about how we use what we have, as fewer of us eating more resource heavy foods plainly has a larger impact that bigger populations eating more intelligently.

“Not my area of expertise,” says Barrett, describing global fertility. “My understanding is that in many areas of the developed world fertility rates are stable at a low level or falling, and in the developed world rates are stable at a high level.

“I'm not sure what you mean by 'evolutionary' population adaptation. Natural selection acts on individuals, but that can lead to changes in allele frequencies in populations that result in evolutionary change in the population. Population size is not an individual trait, so it's not something that natural selection can act on very effectively.

“There are endless debates about group versus individual selection in evolutionary biology, and while it is possible for group selection to operate, it has been shown that the set of conditions required for it to work are extremely restrictive.”

Time will provide answers regarding whether we really need to act or not. But ei ther way more sensible ways of using the natural resources we have, and not squandering precious water and soil is an obvious move to make.

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