Ghost trade-offs: negative correlations between beneficial traits may be caused by other mechanisms than trade-offs

Although trade-offs are ubiquitous in living nature, they often remain concealed from researchers. Here I describe an opposite possibility: a trade-off may be apparent as a negative across-population correlation between beneficial traits, but not actually present. I describe two simple and mutually non-exclusive mechanisms by which such "ghost trade-offs" can emerge: (a) elimination of the least fit ("double-weak") genotypes, while the moderately fit ("single-weak") trait combinations survive, and (b) evolutionary suicide, i.e., extinction of the most fit ("double-fit") lineages. Such "ghost trade-offs" may be common in nature and should be recognized and distinguished from real trade-offs.