We believe that contact comfort has long served the animal kingdom as a motivating agent for affectional responses. Since at the present time we have no experimental data to substantiate this position, we supply information which must be accepted, if at all, on the basis of face validity
The authors acknowledge that there is currently insufficient experimental evidence to support their theory that contact comfort acts as a motivator for affectionate reactions. They argue that this view is founded on face validity, which is the idea that it makes sense in light of the information that is now available. Put another way, by presenting their argument as a hypothesis that needs more research, the writers are admitting that they do not yet have sufficient data to back it up.