Impermeable seed/fruit coat, i.e. physical dormancy (PY) occurring in seeds of many genera of 19 angiosperm plant families has been traditionally viewed as a form of dormancy that regulates germination timing. However, this view was recently challenged by an alternative explanation claiming that the impermeable seed coat evolved as a coping mechanism to escape predators, i.e. crypsis hypothesis. Here, I wish to call for more careful attention on crypsis as an evolutionary factor because (1) information of volatile compounds is not known in PY families except Fabaceace; (2) impermeability is not induced until the moisture content of the seeds drops below species-specific threshold suggesting that drying determines development of impermeable seed coats; (3) the crypsis hypothesis does not explain the year-to-year or between site variations in proportions of impermeable seeds produced by plants; and (4) dry seeds of species from non-PY families also do not emit volatile compounds, and do not develop impermeable seed coats. For these reasons, it appears crypsis might be an exaptation, i.e., a trait that performs a function for which it was not originally evolved. Based on the available evidence, it is suggested that climate drying might have resulted in evolution of impermeable seed coats. [ABSTRACT FROM AUTHOR]