Thursday, April 29, 2010

Are humans smarter than yeast?

Imagine the classic scientist's petri dish, in which is growing a culture of yeast. Some sugar is introduced into the dish, and the yeast thinks 'food!' - so the yeast population expands as it gorges on the sugar. Sadly, there are bounds to the petri dish, and the amount of sugar is limited. The yeast population expands rapidly, bumps into the limits to growth, and then collapses. For the yeast, think of human population; for the sugar, think of fossil fuels; for the boundaries of the petri dish, think of the earth. Put simply, the problem faced by the yeast, and the problem faced by the human community on earth, is the same – exponential growth cannot continue for ever in a finite space. Human society is facing a similar situation, and the only question is – can we do better than the yeast?

Exponential growth occurs whenever something grows at a constant rate – for example, an economy that is growing at 5% a year. So if we begin with 100 widgets of production, and our production grows by 5% then after 1 year we will have 105 widgets. If the growth continues then after another year we will have 110.25 widgets. After another year we will have 115.7625 widgets. Notice that the amount added on increases each time – 5 widgets in the first year, 5 and a quarter in the second year, five and a half in the third year. That is because the underlying quantity has increased. So exponential growth is not simply adding on a fixed amount each year, it is adding on an increasing amount each year.

The interesting thing about exponential growth, and what makes it so marvellous and miraculous and devastating, is something called 'doubling time'. When a certain percentage of growth is maintained over time then we can expect the underlying quantity to double at a particular rate. For example, if growth is maintained at 7.5% a year then the underlying quantity will double (approximately) every ten years. Which brings us to the famous tale of the chessboard and the king. The tale goes – and it is entirely apocryphal so it has been told many ways – that a great inventor gave the king a chess set. The king was greatly pleased with the gift and asked the inventor what he would like as a reward. The inventor asked that a grain of rice be placed on the first square, two grains of rice on the second, four on the third, eight on the fourth and so on round all the 64 squares of the chessboard, doubling each time, and that he be given the total quantity of rice that would end up on the board. The king readily agreed and asked his treasurer to dispense the rice. After taking some time to work out how much this would be, the treasurer told the king that it amounted to more rice than was available in the whole world – at which point the king decided the inventor was more trouble than he was worth and had his head chopped off.

When a population embarks upon exponential growth in response to a sudden abundance of food ecologists call it 'overshoot'. In a situation of temporary abundance (the food supply for the yeast) there is a short period of exponential growth leading to a population explosion (lots more yeast); once the temporary abundance has been exhausted then there is a crash while the system returns to an equilibrium (a very small part of the yeast population survives). The human population of the earth has been growing exponentially, and the numbers have exploded through the second half of the twentieth century and into the twenty-first. However, just as with the yeast, exponential growth cannot go on forever and it will come to an end.

This is not a new insight. It was first popularised through work sponsored by the Club of Rome in the early 1970's and published as 'The Limits to Growth'. This was a work that was more misunderstood and maligned than actually read and considered. However, time has shown the essential insights of that report to be correct. The conclusion of the report was that, if nothing was done to amend the path that our culture had embarked upon then, in the early decades of the twenty-first century, our economy would start to hit the ecological resource limits and further growth would be prevented. In other words, around about now.

The best way to understand this is to think about physical economic growth as a cancer. Just as a tumour is a part of a body which is growing rapidly, without any regard to the health of the wider organism, so too is exponential growth of our physical economy something which will destroy the wider human and planetary ecology on which it depends. If we continue to pursue economic growth at all costs, then a fate very much like that of the yeast in the petri dish awaits us. Can we do better than the yeast? (Something to ponder at this time of a general election, when politicians promises to restore “growth”).

To my mind, the predicament we face is not a practical problem requiring practical solutions, but a challenge to our values. We need to work out what it is that we really want to preserve in our society, and what we are prepared to do without. This is an essentially spiritual task. More on that in the next issue.


  1. "This is not a new insight."

  2. The old ones are the best :)

    But of course, technology will save us. Always has, always will. Especially on Easter Island.


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