Human hands are delicate and efficient instruments. each one contains 27 bones, one more than each human foot. each also contains muscles and tendons which react to nerve stimuli. it is these reactions which enable people to clench and grasp. the thumbs are, perhaps, the most important part of each human hand. they are opposable, which gives them their unique movement. besides humans, only apes have opposable thumbs. the ability to grasp is probably responsible for much of human progress.

Look at the images of different rocks. which rocks have a fine-grained texture? check all that apply. 1 2 3 4 5

To answer this question, researchers studied populations of the dusky salamander (desmognathus ochrophaeus) living on different mountain ranges in the southern appalachian mountains. the researchers tested the reproductive isolation of pairs of salamander populations by leaving one male and one female together and later checking the females for the presence of sperm. four mating combinations were tested for each pair of populations (a and b)—two within the same population (female a with male a and female b with male b) and two between populations (female a with male b and female b with male a). the proportion of successful matings for each mating combination was measured. for example, when all the matings of a particular combination were successful, the researchers gave it a value of 1; when none of the matings were successful, they gave it a value of 0. then the researchers calculated an index of reproductive isolation that ranged from 0 (no isolation) to 2 (full isolation). the reproductive isolation value for two populations is the sum of the proportion of successful matings of each type within populations (aa + bb) minus the sum of the proportion of successful matings of each type between populations (ab + ba). the table provides data for the geographic distances and reproductive isolation values for 27 pairs of dusky salamander populations.

Patient has just received an organ transplant which treatment would be most effective in preventing the patient’s body from