Does " strain the credulity" mean "emphasize the vulnerability"?

Context:

Some of these may have been lost in one species or the
other, but many of them remain in a position that is most
consistent with their having arrived in the genome of a com-
mon mammalian ancestor, and having been carried along
ever since. Of course, some might argue that these are actu-
ally functional elements placed there by the Creator for a
good reason, and our discounting of them as "junk DNA" just
betrays our current level of ignorance. And indeed, some
small fraction of them may play important regulatory roles.
But certain examples severely strain the credulity of that ex-
planation. The process of transposition often damages the
jumping gene. There are AREs throughout the human and
mouse genomes that were truncated when they landed, re-
moving any possibility of their functioning. In many in-
stances, one can identify a decapitated and utterly defunct
ARE in parallel positions in the human and the mouse
genome (Figure 5.2).