The underdog, Canis basus, is a species of the Canidae that is found exclusively in urban habitats. In contrast to other members of the same family, the underdog is a solitary creature, living mostly in basements and sewers, and seldom seen in the light of day.
The origin of the species is unknown, but it is believed that the underdog separated from the common dog, Canus lupus familiaris, about two thousand years ago. Although this timespan is extremely short for pronounced speciation in a mammal, behavioral, morphological and genetic analysis leave no doubt that the underdog is indeed a separate species.
Its body is smaller than that of other dogs, and its teeth are more adapted to a diet consisting exclusively of carrion and leftovers. Genetic differences can be observed in the nuclear as well as mitochondrial DNA, and are believed to be responsible for the underdog’s extremely efficient metabolism. Indeed, and underdog can survive on one hundred grams of fetid meat (3.5 oz.) for several days without showing any signs of fatigue or reduced activity.
A recently emitted theory for the appearance of the underdog suggests that the species separated from the dog mainly because of behavioral traits, namely its reduced social affinity. The individuals that separated from the group would mate with each other, reinforcing the genetic disparity between the two species-to-be. Morphological and genetic changes would follow to account for the solitary lifestyle.
The example of the underdog does illustrate the importance of behavioral differences in speciation quite nicely. Often overlooked by pundits, behavioral differences are the first signs of speciation, and differences therein are considered one of the main factors for reproductive isolation in early speciation events that happen without physical separation of individuals.
Even today, it is believed that singing birds living in urban areas are becoming reproductively isolated from those in more rural settings, because they adapt their singing to be heard over the noise of the town. This difference in tune prohibits them from attracting, or being attracted to, their rural cousins.