Although what causes pedophilia is not yet known, beginning in 2002, researchers began reporting a series of findings linking pedophilia with brain structure and function: Pedophilic (and hebephilic) men have lower IQs,[75][76][77] poorer scores on memory tests,[76] greater rates of non-right-handedness,[75][76][78][79] greater rates of school grade failure over and above the IQ differences,[80] lesser physical height,[81] greater probability of having suffered childhood head injuries resulting in unconsciousness,[63][82] and several differences in MRI-detected brain structures.[83][84][85] They report that their findings suggest that there are one or more neurological characteristics present at birth that cause or increase the likelihood of being pedophilic. Evidence of familial transmittability "suggests, but does not prove that genetic factors are responsible" for the development of pedophilia.[86]