Does "mouthful" here mean "meaningful word"?

Context:

This view explains altruism at the individual level in nature, especially in kinship relationships: when an individual sacrifices its own life to protect the lives of kin, it is acting in the interest of its own genes. Some people find this metaphor entirely clear, while others find it confusing, misleading or simply redundant to ascribe mental attributes to something that is mindless. For example, Andrew Brown has written:

"Selfish", when applied to genes, doesn't mean "selfish" at all. It means, instead, an extremely important quality for which there is no good word in the English language: "the quality of being copied by a Darwinian selection process." This is a complicated mouthful. There ought to be a better, shorter word—but "selfish" isn't it.[2]