Animals often have very different numbers of active genes related to any sense. For instance, most fish or even aquatic mammals have very few olfactory receptor genes, whereas this is higher in terrestrial animals. Even among them, there is huge variation; compare dogs and humans, for instance. But this comes at a cost; for instance, dogs are dichromatic, the blind mole is, well, blind. So there is a compensation across the senses which is not merely a plastic change. I was wondering if there is any way to reconcile this with some notion of conservation of the total proportion of active genes involved with sensation.
There are two notions I could think of
There might have a trade-offs about where to spend ressources (energy and nutrients). If an organism spend a lot of ressources in, say, vision (incl. the part of the brain that deal with interpreting the input), then there won't be much left for other things.
When a sensory system is well enough developed that the other sensory systems would bring up only marginal benefits, it is better to just not spend unecceesary ressources on building these other sensory systems.
Please note that
The above two hypotheses are just guess work from me and I did not support any of what I said with an actual evidence.
I assumed that there is a negative correlation between the "quality of the different sensory systems" (whichever way that would be defined) but I don't know whether this is true or not.