Why are honey possum L cones tuned to longer wavelengths than other marsupial L cones?
Why are honey possum L cones not tuned to longer wavelengths still? Before we consider these questions in turn, it is important to note that an adaptationist approach can never definitively answer such questions about evolutionary causes. There will always be other possible pressures or constraints than the ones tested, or it may be that the trait in question has not itself been selected at all, but is a `spandrel’ (i.e. a byproduct of selection for another trait; Gould, 1997; Gould and Lewontin, 1979). Furthermore, the properties of sensory systems may be a compromise between many pressures, which may be one reason why the critical sensory tasks that affect the fitness of an individual animal are difficult to identify, despite sensory systems generally being considered to be subject to strong selection pressure. It is also important to distinguish between pressures that may operate on a trait now and the pressures that may have contributed to its selection in the past, and even a clea
