What is the universe made of?

Why do people need to sleep?

How does a person's body know when to stop growing?

These are among the 125 Biggest Unanswered Questions in Science, according to more than 100 leading scientists who were recently asked what they thought were the most glaring holes in humankind's understanding of the world.

Answering these tough questions could take decades or longer, and will require work by many of the greatest minds in science. But it's interesting that many of the questions submitted by top scientists are the same ones kids typically wonder about.

Such as: "How do migrating butterflies, birds and other animals find their way?" "Why do we dream?" "Could a machine learn to think?" "Does the human brain automatically know the difference between right and wrong?"

That sharing of curiosities strengthens the thought that kids are natural scientists.

The project was the idea of editors at Science magazine, in which many kinds of researchers publish their findings. The journal, founded by inventor Thomas Edison, is celebrating its 125th anniversary. Its first issue, published July 3, 1880, had 12 pages on the futuristic possibility of making electric-powered trains, an article describing the latest observations of a star cluster known as the Pleiades, and advice for science teachers on the importance of studying animal brains.

Some of the big questions on this year's list have been around since the journal started:

* "What is the biological basis of consciousness?" (That is, what is thinking, really, and how does it happen?)

* "How much can human lifespan be extended?" (The average American lifespan has increased from 49 years to 77 years in the last century, and some people think that before long it may be common to live to 120.)

* "Are we alone in the universe?" (Many scientists believe that with so many galaxies, suns and planets, there must be somebody else out there.)

* "How are memories stored and retrieved?"

But other questions on the list could not have been asked even 10 years ago. For example: "Why do humans have so few genes?" (Only recently did scientists learn that all the instructions for making a human being are contained in some 25,000 genes, about a quarter the number scientists expected and not much more than that of a fruit fly or worm.)

Of course, there are plenty of questions that kids want answers to that grown-ups haven't thought much about -- yet.

Ginger Pinholster, who works for Science magazine, said she was impressed by a question from a kid who attended a recent meeting with his parents. The boy asked a scientist who had cloned mules whether those mules, being genetically identical, had the same memories. (The answer is no, but it wasn't a question the scientist had prepared for.)

Pinholster, who has a 9-year-old daughter and so sometimes thinks like a kid, confesses that she has long wanted to know whether giraffes, with their ridiculously long necks, can throw up.

That question did not make the list.

-- Rick Weiss