It is striking that evidence for hyperostosis frontalis interna - a phenomenon of exclusive bilateral thickening of frontal endocranial surface - in archaeological samples is very rare in contrast to its modern prevalence. Because microevolutionary changes have been shown for various human characteristics any alteration of hormonal levels is very likely. Selection pressure was definitively higher in earlier times. This favoured prolonged alertness in order to access sufficient food, shorter feeling of satiety, lower level of fat metabolism, lower metabolic rates and, therefore, lower level of leptin - a 167 amino acid peptide mainly involved in human total body fat regulation. Its effects on bone metabolism are still debated. Nevertheless, we postulate the following hypothesis: In humans a decrease of selective pressure favoured an increased metabolic rate. This, being related to the higher level of leptin caused an increase of localized bony overgrowth like hyperostosis frontalis interna.