but in a pragmatic sense, whatever difference separates a duck from a robin and would make a disease less likely to spread from a duck to a robin, must also be a difference between a robin and a duck, and would make a disease less likely to spread from a robin to a duck
What? No. It’s not even vaguely reasonable to say that a transfer of a disease between two species is equally likely either way.
The differences between gray and red squirrels make it entirely certain that a particular disease will pass from gray to red, but not red to gray—grays carry the virus responsible in their DNA and are immune to it, but it kills reds.
Now, if you could show that people had a strong tendency to always assume that it would be easier to pass disease from something quite like the stereotypical example of a category to a non-stereotypical example than the other way around, you’d have something. As it is, you only have an anecdote.
What? No. It’s not even vaguely reasonable to say that a transfer of a disease between two species is equally likely either way.
The differences between gray and red squirrels make it entirely certain that a particular disease will pass from gray to red, but not red to gray—grays carry the virus responsible in their DNA and are immune to it, but it kills reds.
Now, if you could show that people had a strong tendency to always assume that it would be easier to pass disease from something quite like the stereotypical example of a category to a non-stereotypical example than the other way around, you’d have something. As it is, you only have an anecdote.