21.   Similar kinds of collective phenomena are a hallmark of biological systems, he said.

22.   The Howard Hughes Medical Institute has chosen as its next president Thomas R. Cech, an expert on the chemistry of biological systems.

23.   The problem is that most biological systems remain too complex for science to predict how they will react to theoretically valuable treatments.

24.   They have uncovered abnormalities in the biological systems controlling hunger and satiety that may play a role in many eating disturbances.

25.   They prefer a biological system like the undergravel filtration.

26.   What is particularly worrisome is that because biological systems reproduce, such genetic pollution cannot be cleaned up like a chemical spill or recalled like a defective automobile.