What do molecular laws of life mean for species: absolute restrictions or mere suggestions?

Evolutionary biologists are interested in finding universal patterns of covariation between macroscopic and molecular traits. Knowledge of such laws of life can be essential for understanding the course of evolutionary processes. Molecular parameters are presumably close to fundamental limits set to all organisms by laws of physics and chemistry. Thus, laws of life that include such parameters are hypothesized to be similar at both wide interspecific levels of variation and narrower levels of intraspecific and intraindividual variation in different species. In this Commentary, I discuss examples where the significance or direction of such molecular laws of life can be compared at different levels of biological variation: (1) the membrane pacemaker theory of metabolism, (2) the correlation between variation in metabolic rate and mitochondrial efficiency and (3) the allometric scaling of metabolism. All three examples reveal that covariations within species or individuals that include molecular parameters do not always follow patterns observed between species. I conclude that limits set by molecular laws of life can be circumvented (at least to some degree) by changes in other traits, and thus, they usually do not impose strict limitations on minor within-species evolutionary changes (i.e. microevolution). I also briefly discuss some of the most promising perspectives for future studies on the universality of molecular laws of life.