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 (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
4000 BC, cobs were already an inch long. Within just a few thousand
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.
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.
Even to this day, we're still producing new types of watermelon — like the black Densuke watermelon grown on a single island in Japan. And crop scientists have produced seedless watermelons by adding chemicals to double a watermelon's chromosomes and then breeding the result with a normal watermelon.*
The evolution of peaches
(James Kennedy)
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.)
Further reading:
You can see many of Kennedy's other wonderful graphics on his blog. He also, for instance, had a fun series showing the ingredients inside bananas orstrawberries.
No comments:
Post a Comment