That hypothesis isn&#x27;t falsifiable. We know &quot;X effects Y&quot; from experimental result. You&#x27;re asking for proof that &quot;X and only X effects Y&quot;, which is the same as asking for &quot;There does not exist some X&#x27; that effects Y&quot; where the set of X&#x27; is unbounded. No, that&#x27;s not testable and doesn&#x27;t need to be.<p>Just like we didn&#x27;t need to know about the X&#x27; of Einstein&#x27;s equations to know that the X gravity was the primary force holding you to the ground.<p>There very well may be an X&#x27; that effects observable biological features other than evolution, but that X&#x27; needs to be tested on an individual basis. So while it&#x27;s productive to hypothesize an X&#x27; and test it, there&#x27;s not much we can do to rule out all X&#x27; as a class.