A few days ago an interesting paper entitled "Character displacement of Cercopithecini primate visual signals" was published in Nature Communications by a researcher from New York and two from the UK (click HERE to see a summary of the paper).
The authors introduce their study as follows: "Individuals from closely related species are often at risk of mating with each other and producing hybrids with reduced fitness. In addition to the reproductive disadvantages of interspecific matings, there may also be ecological advantages that favour mixing with individuals of the same species in tasks such as foraging. Theory predicts that costly mismatings and associations with heterospecifics can be avoided by the evolution of species recognition signals that reliably identify individuals of the same species. To improve discrimination between groups, species recognition signals are expected to undergo character displacement whereby phenotypic differences between two or more populations become accentuated where their ranges overlap.", and they conclude by saying "In summary, we have shown that in a large tribe of primates, face patterns have evolved to be especially distinctive from those that they share more of their range with. The likely cause of this relationship is that face patterns function as species recognition signals to promote and maintain reproductive isolation between species through either ecological or reproductive character displacement. The observed pattern is likely the result of the process of reinforcement [my emphasis], a key mechanism that can create new species." So what has all of this got to do with Alfred Russel Wallace you may ask? Well, Wallace not only devised the theory of reinforcement - often called "the Wallace Effect" - but he also devised the concept of "recognition marks" in 1877 as a specific mechanism by which the Wallace effect could operate. Sadly the authors of the study under discussion here, in common with most other biologists, are currently unaware of Wallace's major theoretical contributions to this subject - so not surprisingly Wallace's work on the subject was not cited in the paper in question.