As Darwin came to understand, evolution was the product of billions of tiny “experiments” in survival and fecundity, the outcome of which decided which individuals, with which traits, became parents to the next generation. Over time, the statistical odds favor the retention and spread of these adaptive differences and the loss of any that are counterproductive – an albino deer, for example.

In summary, the key ingredients in Darwin’s schema were diversity, inheritance, selection and time. It was the interaction and the impact of the combination of these (see Figure 1) that Darwin was the first to unveil.

and breeding experiment, suggesting that someone sow kidney beans, “…so early that a very large proportion are destroyed by frost, and then collect seed from the few survivors, with care to prevent accidental crosses, and then again get seed from these seedlings, with the same precautions…”

Modern genebanks and plant breeders are essentially doing this today on a large scale and with many crops. Drawing on the huge diversity stored in genebanks, breeders expose samples to different conditions (heat, drought, a new disease) to find the adaptive traits for producing the new varieties that farmers will sow in the future. But if this genetic diversity is not conserved, if we lose the ability to make and accumulate those small changes so central to evolution, we will have removed one of Darwin’s essential pillars of evolution – variation – and will have rendered selection impotent.

The diversity of our crops – what we have managed to save of it – is what humans will have to fashion those small incremental adaptive changes in crops necessary for their survival. Climate change and other pressures on agricultural systems and crops intensify daily. Agriculture needs to respond, even now, with crop varieties adapted and ready to meet these challenges. What better way to commemorate Charles Darwin’s life and work than guaranteeing that agriculture’s evolutionary process can continue.

America’s new President, Barack

Obama, said in his inaugural address, “What is required of us now is a new era of responsibility… this is the price and promise of citizenship.” For the world’s food supply, good global citizenship requires us to embrace our “evolutionary responsibility.” It remains to be seen whether we are prepared to pay its price.

Responsibility

Sir Ronald Fisher, an early and prominent geneticist, contended that the smaller the change, the more likely it would be positive. He used a microscope analogy. A tiny movement in the objective lens has a 50% chance of being in the right direction and improving focus. A large movement in the lens, whether in the right or wrong direction, is likely to worsen the focus.

So it follows that dramatic changes in organisms from one generation to the next, as a result of a major mutation, rarely succeed. Huge random changes have the potential to take an organism in countless directions, many, indeed most of them probably unviable. The resulting organism simply is not adapted to the environment in which it was born. Changes of a more limited scope will be less dramatic, but will stand a better chance of building on an existing success – that of the parents. As Dawkins puts it, “however many ways there may be of being alive, it is certain that there are vastly more ways of being dead.” The small steps, not the giant leaps, are the most likely to succeed.

And this brings us, finally, to the connection with crop diversity. Unlike wild species, crops are domesticated. Their fitness, their evolution is in our hands and as Sir Otto Frankel put it, “We have acquired evolutionary responsibility.”

Darwin understood that populations that made appropriate and successful adaptations survived and that those that didn’t perished, and that agricultural crops were not exempt. He noted, for example, that certain crop varieties “withstand certain climates better than others” and in Origin, outlined a screening

Editor’s note: Reprinted with permission from the Global Crop Diversity Trust.

 

This article is part of a regular series on the subject of crop diversity topics. More articles in this series can be found at www.croptrust.org.