Savulescu summary 2

-        Aliens example: one example provided is of aliens from a faraway galaxy which are strikingly like humans. These aliens are not only interfertile with humans, but they are genotypically similar. However, the authors suggest that these factors alone would not be enough for us to consider the aliens to be a member of our species (657).

Gull example: In this example, the authors discuss the herring gull and black-backed gull. Both species of gull are found in Europe but are genetically distinct and cannot breed. However, the black-backed gulls found in North America are much more similar morphologically and genetically to herring gulls. If we were to then classify the North American black-backed gulls and the herring gulls, by transitive property, the black-backed gulls of Europe would then be of the same species as herring gulls. The authors point out that if species sameness is enough to link the two gulls, but they cannot be linked because they are not interfertile, it presents a counterintuitive dilemma with species classification.