If you compare a modern cotton crop with one grown 1,600 years ago, the DNA of the two look almost nothing alike. It’s the first known example in domesticated crops of a supercharged evolutionary phenomenon known as punctuated equilibrium.
We tend to think of evolution as a slow, gradual process, with adaptive changes taking hold over periods of at least several thousand years. That was the view favored by Charles Darwin, and it’s defined the popular view of evolution for 150 years. The alternative view, first proposed by Niles Eldredge and Stephen Jay Gould in 1972, is that of punctuated equilibrium, in which most evolutionary changes are compacted into an incredibly short timeframe, with the vast majority of a species’s existence spent in an unchanging state known as stasis.
While punctuated equilibrium isn’t exactly the consensus view in evolutionary biology - Richard Dawkins is one of its most famous critics - there are some rather compelling examples of this mechanism in action, and new DNA analysis from the University of Warwick has turned up a particularly spectacular example. Cotton, which was only domesticated around 6,500 years ago and so represents an inherently short evolutionary timescale, turns up a striking case of punctuated evolution.
The researchers compared ancient remains from Egypt’s Upper Nile region that date back 1,600 years. The modern equivalent of this crop shows a significantly reorganized genomic structure. In just about a millennium and a half, something happened to rewrite drastically the cotton DNA. And while domestication can definitely cause some major biological changes to an organism, this happened a few thousand years after the crop was altered for human use.
What’s more, analysis of similar cotton species from South America show just how stable this crop generally is. Samples from Peru and Brazil dating between 800 and 4,000 years old - spanning 3,200 years and over 2,000 miles - are virtually identical. That genomic stability suggests similar stasis in the Egyptian cotton crop, with the sudden burst of punctuated evolution rewriting its genome in response to some environmental stress 1,600 years ago. In a statement, lead researcher Dr. Robin Allaby discusses what could have possibly spurred this supercharged adaptation:
“We think of evolution as a very slow process, but as we analyse more genome information we can see that there’s been a huge amount of large-scale proactive change during recent history. Our results for the cotton from Egypt indicate that there has been the potential for more adaptive evolution going on in domesticated plant species than was appreciated up until now. Plants that are local to their particular area will develop genes which allow them to better tolerate the stresses they find in the environment around them. It’s possible that cotton at the Qasr Ibrim site has adapted in response to extreme environmental stress, such as not enough water.”
Allaby also suggests this information could be crucial in determining how well crops will handle the sudden environmental changes brought on by climate change. If that’s the case, I guess we should cross our fingers that these crops have another round of seriously speedy evolution left in them.