In doing a little looking around, I found three different answers to the question: What percent of cats are susceptible to catnip?
- The Humane Society says "an estimated 50 percent"
- Scientific American says "about 70 to 80 percent"
- Cat World says "around 50–66%"
Each source carefully notes the figure as an estimate. None of them cite any sources or give any explanation beyond the figures coming from "experts." (You'd think someone would take a poll, but that's not my point)
I recall hearing many years ago that the gene for catnip sensitivity followed a simple dominant-recessive pattern. Similar to Mendel's peas, in a well-mixed population, you'll have the pairs RR, Rr, rR, and rr - only 25% (the rr group) will not express the trait, the other 75% will. That would lend support to Scientific American's numbers.
However, if the genes that cause catnip sensitivity exhibit some form of co-dominance, like human blood groups, then the percentages can skew.
So my question comes down to: What hard-science exists to explain the variation in sensitivity to catnip among cats? Have there been any long-term breeding experiments? Has that portion of the feline genome been explored at all?