Whilst the proximate mechanisms underlying these behavioral differences have been investigated, the ultimate causes have not.
High-risk studies consistently reported that while infants later diagnosed with ASD exhibit signs of the condition at 12 months (e.g., lack of eye contact, reciprocal smiling, and social engagement), no such behavioral differences have been reliably detected at 6 months [ 17].
Prenatal restraint stress was further shown to reduce dentate granular cell number, but only in female offspring [52], while also other sex-related behavioral and structural differences have been reported [48].
Notably, a number of inbred mouse strain differences have been documented for physiological and behavioral phenotypes relevant to human mood disorders.
The dorsal ventral dimension is orthogonal to the fractionation-unification distinction in that dorsal ventral differences have been proposed for many individual behavioral domains.
Behavioral differences haven't been able to explain it all, though.
The difference has been growing and observable "for multiple diseases, biological and behavioral risk factors, and injuries".
In addition to the above-mentioned geographical and behavioral differences, there has been a recent boost in European studies investigating physical environmental correlates of PA in adult populations, making it relevant to update the existing European literature on this topic.
Genotypic differences resulting in behavioral variation have been widely documented as well; one of the most dramatic examples of this is variation in defensive behavior between Africanized and European strains of honey bees [24], [25].
Inter- and intra-species variations in the expression pattern of AVPR1A in the brain and downstream differential behavioral phenotypes have been attributed to differences in the non-coding regions of the AVPR1A gene, including polymorphic elements within upstream regulatory areas.
Individual differences in metabolism and behavioral phenotype have been posited to be correlated (Careau et al. 2008; Biro and Stamps 2010; Houston 2010), and metabolism has been associated with behavioral phenotype in adults (Mus domesticus, Rezende et al. 2009; Peromyscus maniculatus, Careau et al. 2011; Canis familiaris, Careau et al. 2010; Microtus oeconomus, Lantová et al. 2011).
