41.   Nature has a third option for shaping behaviors -- the absence of positive reinforcement.

42.   Nature has it worked out.

43.   Nature has its own order, of course.

44.   Nature has methods, but they take longer.

45.   Nature has patience with these things, too.

46.   Nature has rude ways of complaining when people step too heavily on it.

47.   No matter how talented he was, nature had the upper hand and the final say.

48.   Problems arise when the nature of the competition has to be explained.

49.   The avalanche of human genome data being made available now actually tells researchers relatively little, other than that nature still has many secrets to reveal.

50.   The lyrics tell heart-breaking stories of alienation, loss and the power nature has over humans.