  We describe a large class of chemical reaction networks, those endowed with a
subtle structural property called concordance. We show that the class of
concordant networks coincides precisely with the class of networks which, when
taken with any weakly monotonic kinetics, invariably give rise to kinetic
systems that are injective --- a quality that, among other things, precludes
the possibility of switch-like transitions between distinct positive steady
states. We also provide persistence characteristics of concordant networks,
instability implications of discordance, and consequences of stronger variants
of concordance. Some of our results are in the spirit of recent ones by Banaji
and Craciun, but here we do not require that every species suffer a degradation
reaction. This is especially important in studying biochemical networks, for
which it is rare to have all species degrade.
