A year of twists and turns. (Science News of the year: the weekly newsmagazine of science).

What the world needs, say some people, is more one-handed scientists. That way, reports would have fewer sentences starting, "On the other hand ..."

Actually, scientists need all the hands they can muster. Most of the phenomena they investigate are so complex that even carefully designed experiments can't take into account all possible influences on the results. Change one condition--a chemical concentration, a nutritional state--and an experiment can yield dramatically different data. Or worse, factors that scientists haven't even considered can turn out to be the main drivers. What scientists know for sure is that today's conclusions may well be overturned by tomorrow's data.

This frustrating aspect of science was magnificently demonstrated this year with the surprising findings of two trials of hormone-replacement therapy. Previous studies had convinced doctors to prescribe estrogen and progestin supplements to millions of women, primarily to prevent heart disease. But in large, rigorously designed U.S. studies, women receiving the treatment experienced more blood clots and either more or the same amount of heart disease and strokes than did the women who didn't get the supplement (SN: 7/27/02, p. 61).

Luckily, not every follow-up study contradicts earlier work. The longest follow-up studies on breast cancer surgery confirmed that the breast-sparing surgery called lumpectomy benefits women just as much as having an entire breast removed (SN: 10/19/02, p. 243).

Yet many. of the 2002 scientific findings that we list below challenge earlier results. Mars may not have had a continuously warm, wet past. Neutrinos have mass after all. Diamond isn't the sturdiest material.

So, what you learned in school years ago--or what you read just last year--doesn't necessarily correspond with today's scientific conclusions. To keep current, you'll want to follow the twists and turns as researchers apply new technologies and carry out larger, longer, and smarter studies. At Science News, now in its 80th year of publication, all hands are devoted to keeping you up-to-date with timely, concise reports.