(paraphrasing pgs: 138-9 )
The story begins in 1856 when a Spanish medical doctor did an autopsy on a 40-year-old man who had no sense of smell, a small penis and very small testes.
Anyway, many years later, it turns out, embryologically speaking, that the primitive cells for smell send axons to the area of the brain that will form the olfactory lobe. On their way, they lay down, and travel along, fascicles/rails to get there. If anosmin is not present the axons derail, and the rails do not get laid down....hence anosmia.
Amazingly, the cells for sexual development in males begin in the nose, in the vomeronasal organ. They neuronally migrate along the rails/fascicles laid down by the developing olfactory axons. In the absence of anosmin and the rails, the cells never reach their target to trigger the release of gonadotropin releasing hormone. In the absence of gonadotropin releasing hormone, the pituitary is never stimulated to release leutinizing hormone… hence the small penis/testes.
Gentlemen, you know who you are.
Go figure…evolution; incredibly efficient, and funny too!
I gotta go… I smell something in the other room that requires my immediate attention.