雞下蛋，蛋孵雞，這周而復始的循環到底從哪里開始？科學家們提出了一種解釋--雞由鳥進化而來，鳥由恐龍進化而來，而恐龍從蛋里孵出來。那就是先有蛋嘍？讓我們一起來看個究竟吧。
Chicken or egg? Like a hall of mirrors at the
carnival, each attempt at an answer just leads to another question. If the
chicken came first, then didn't it hatch from an egg? And if the egg came first,
wasn't it laid by a chicken? It's one of those questions that seem unanswerable.
Scientists agree on where chickens came from: In a sense, human beings
invented them, just like they invented cows and pigs and other domesticated
animals on Old MacDonald's Farm.
If chickens were interested in tracing their family trees, they would need to
bone up on some DNA research done in
Japan. Every chicken that ever lived can trace its ancestors, say researchers,
to a particular subspecies of Red Jungle Fowl in Thailand.
The male Red Jungle Fowl looks a lot like a storybook rooster. But the Jungle
Fowl isn't identical to a farm chicken. Unlike chickens, female Red Jungle Fowls
have no combs. Another Jungle Fowl
peculiarity: After mating season, males replace their bright red and orange ruff
with a crop of dull, blackish feathers called "eclipse plumage."
Scientists think the first domestic chickens were bred from Red Jungle Fowls
more than 8,000 years ago in the region now divided into Thailand and Vietnam.
People bred chickens first for cockfighting contests, later for eggs and meat.
So the first official "chicken" pecked its way out of an egg laid by a bird
that was not-quite-a-chicken. Depending on how you look at it, the egg--or the
wild chicken--came first.
In creating the domestic chicken--and coming up with some 175
varieties--human beings also created a world where chickens rule the roost:
There are more chickens than any other kind of domesticated bird on Earth.
And where did birds come from? Scientists think that a group of egg-laying
feathered dinosaurs were probably the ancestors of today's birds. So if it
weren't for dinosaurs, there wouldn't be any Jungle Fowl OR chickens.
We've solved the riddle of where chickens came from. But there's still the
question of where eggs came from.
Scientists say eggs--handy miniature incubators of life, nutrients already packed
inside--evolved more than 1 billion years ago, in the oceans of Earth. When land
animals evolved about 250 million years ago, their eggs had a tough covering to
retain moisture on dry land. Egg-layers like amphibians, reptiles, and insects
flourished. The first "land eggs" pre-dated chickens by about 249,992,000 years.
So "the egg" may be one answer to the old riddle, but here's another, if a
little longer: The chicken came after the bird, the bird came after the
dinosaur, the dinosaur came after the egg. And the egg came long after the first
single-celled bacteria, the prokaryotes, evolved in the oceans, some 3.5 billion
years ago.
bone up on: 專心致志于
comb: 雞冠
incubator: 孵卵器
（來源：www.how-come.net 實習生江巍）
