Here’s what 9,000 years of breeding has done to corn, peaches, and other crops
Fruits and vegetables have changed a lot since the onset of agriculture 10,000 years ago, as generation after generation of farmers artificially bred crops to select for more desirable traits like size and taste.
But that change can be hard to visualize. So James Kennedy, a chemistry teacher in Australia, created some terrific infographics to show just how drastic the evolution has been. This one, for instance, shows how corn has changed in the last 9,000 years — from a wild grass in the early Americas known as teosinte to the plump ears of corn we know today:
The evolution of corn
The evolution of corn (maize) is a fascinating story. For a long time, scientists couldn’t figure out where domesticated corn originally came from — it doesn’t look like anything that grows in the wild. It took serious sleuthing by geneticists, botanists, and archaeologists to figure out that maize split off from teosinte grass some 9,000 years ago. (The two are surprisingly similar at the DNA level, differing by just a handful of genes.)
As maize became domesticated in Mesoamerica, it was radically altered through selective breeding. Early farmers would examine their plants and save the seeds of those that were larger, or tastier, or whose kernels were easier to grind. By 4,000 BC, cobs were already an inch long. Within just a few thousands years, cobs had grown to many times that size. Later on, plant hybridization became an important breeding method to further cultivate certain traits.
Nowadays, corn is grown all over the planet, and humans are still making changes using more advanced breeding techniques. In the 1980s, for instance, seed companies turned to genetic engineering — so, for instance, scientists inserted genes from Bt soil bacteria into corn to help the plant ward off pests. And some researchers are hoping to develop corn varieties that can withstand drought.
The evolution of watermelon
Here’s another great graphic from Kennedy. Modern-day watermelons don’t look anything like their distant ancestors from southern Africa. That, too, is the result of thousands of years of breeding. Yet a few of the biggest advances also came in the United States in the 1950s and 1960s, when crop scientists helped breed varieties that were resistant to disease and had a thicker rind — allowing watermelons to be grown all over the country.
The evolution of peaches
And here are peaches, which started out in China and were selected for size and juiciness over thousands of years. Note that the water content of peaches has changed drastically in just 6,000 years.
Mind you, not all attempts at selective breeding turn out so well. As Sarah Yager recently wrote at The Atlantic, apple-growers in the United States during the 20th century tried to breed Red Delicious apples to be as bright and shiny as possible and stay on shelves for as long as possible without noticeable bruising. The result? “As genes for beauty were favored over those for taste, the skins grew tough and bitter around mushy, sugar-soaked flesh.” Nowadays, as storage and transport have become more advanced, tastier apple varieties like the Honeycrisp or Gala are surpassing the Red Delicious.
(Thanks to Calestous Juma for the pointer to Kennedy’s blog.)
* Correction/update: An earlier version of this post implied that seedless watermelons were also produced through selective breeding. That’s not really a good description — the chemical colchicine is used to double the number of chromosomes in a watermelon. The resulting watermelon is then bred back with a regular watermelon to produce a new plant with no seeds.
A related earlier story: “Traditional crop breeding” isn’t nearly as traditional as you think
Another related earlier story: Those ubiquitous “all-natural” labels on food are meaningless. Let’s get rid of them.
How GMOs conquered the United States.
It might help to distinguish genetic engineering from traditional techniques for producing food.
Humans have been selectively breeding plants and animals for tens of thousands of years to get certain desired traits. Over time, for example, farmers (and scientists) have bred corn to become larger, to hold more kernels on an ear, and to flourish in different climates. That process has certainly altered corn’s genes. But it’s not usually considered “genetic engineering.”
Genetic engineering, by contrast, involves the direct manipulation of DNA, and only really became possible in the 1970s. It often takes two different forms: There’s “cisgenesis,” which involves directly swapping genes between two organisms that could otherwise breed — say, from wheat to wheat. Or there’s “transgenesis,” which involves taking well-characterized genes from a different species (say, bacteria) and transplanting them into a crop (say, corn) to produce certain desired traits.
Ultimately, genetic engineering tries to accomplish the same goals as traditional breeding — create plants and animals with desired characteristics. But genetic engineering allows even more fine-tuning. It can be faster than traditional breeding and it allows engineers to transfer specific genes from one species to another. In theory, that allows for a much greater array of traits.
Here’s a diagram from the Food and Drug Administration: