【英语时差8,16】玉米是如何演化的？
时间：2016-04-12 03:07:12
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（单词翻译）
Don: Mmm. I'm making corn on the cob for dinner, and my mouth is already watering thinking about those sweet juicy kernels1!
Yaël: Yum! Hey Don, how did corn evolve? The seeds are all
crammed2 together on the cob and wrapped tightly inside the thick husks. Seems impossible for the seeds to
disperse3 without a human to peel the husks and separate the kernels.
D: You're right. Corn, or
maize4, only exists in its modern form because of humans. Evidence from archaeological and
genetic5 studies suggests that maize was bred and cultivated by early inhabitants of Mexico as early as ten thousand years ago.
Y: Ten thousand years?! I didn't know people were even farming back then?
D: Not only were they farming, but the early Mesoamericans managed to develop corn from its
grassy6 ancestor by selective breeding. Maize was bred from a wild grain called teosinte.
Teosinte is so unlike modern corn that originally
botanists7 didn't think the two were even related. An ear of teosinte is only about three inches long, with just five to twelve kernels. Compare that to the corn I'll be
munching8 tonight, which can have over five-hundred kernels!
Teosinte kernels also have a "tooth-crackingly" hard shell. But through many generations, ancient Americans selectively bred plants with larger and larger ears, and softer and softer kernels. Now all that is left of that hard shell is the thin tissue that gets stuck between your teeth when munching a cob of corn.
Y: Wow! Lets tip our hats to the ancient Mesoamericans! Thanks to their sophisticated understanding of plant breeding, we have corn for eating,
livestock9 feed, cooking oil, ethanol and even making plastics!
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