H.Allen Orr writes (unfortunately a gated article in The New York Book Review) "Now comes the deep part. Price saw—and it is far from obvious when put into words—that this transmission term can be rewritten mathematically in a way that allows for natural selection at a different biological level. So, to take a simple example, the evolution of height might reflect natural selection between individuals within populations and between populations of individuals. In fact, this mathematical maneuver can be performed recursively, over multiple levels of the biological hierarchy. In the end, the Price Equation allows one to partition evolutionary change in a trait into the possible effects of natural selection acting simultaneously at multiple biological levels, e.g., the species, population, organism, gamete (sperm or egg), and gene.....Crucially, the Price Equation showed that group selection arguments for altruism need not be offered tentatively or apologetically; they could be offered with mathematical precision.....No equation, however elegant, can solve the problem of altruism because the problem, like most in science, is partly empirical. The Price Equation shows that evolutionary change in a trait can be partitioned into the effects of natural selection at different biological levels. But this tells us nothing about the sizes of the effects at these levels." from Is goodness in your genes?