Why are diseases more communicable within a species (e.g. human-to-human) than intraspecies (e.g. bird-to-human)?
In: Biology
Think of organisms as being different media formats. You have a player that is designed to play a certain format and another that is designed for a different format. Let’s take record players for example. You have one that plays 33s and another that plays 45s. If you put the disk from one on the other it won’t sound right. This is sort of how parasites (viruses included) work. They have evolved to function in a specific environment provided by a specific set of hosts. They don’t tend to work all that well outside of their given chain of transmission. However, let’s say you have a mutation that causes your record player to have both 45s and 33 rpm speeds and now allows you to play records of both formats. You can now operate both formats…this is similar to how mutations of a parasite can jump across species. But let’s take it a bit further. Since the player was not originally designed to function with it, it sounds really bad when using the new format. It works, but in a really horrible fashion. In fact it not only sounds awful, but actively destroys the new format discs. This is similar to the reason new parasites can wreak havoc on a new host. They have not evolved to function together, and thus can be pretty virulent.
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