More About Fellatio
Added stimulation at the tip is typically very helpful. In early fetal stages the human anatomy is the same. I believe that is why tend to be more sensitive at the tip, due to the fact, that had they been female. This same anatomical area would have been the clitoris.
A few weeks after fertilization, the initial appearance of the human fetal genitalia is basically feminine: a pair of “urogenital folds” with a small protuberance in the middle, and the urethra behind the protuberance.
In typical fetal development, the presence of the SRY gene causes the fetal gonads to become testes; the absence of it allows the gonads to continue to develop into ovaries Thereafter, the development of the internal reproductive organs and the external genitalia is determined by hormones produced by fetal gonads (ovaries or testes) and the cells’ response to them.
If the fetus has testes, and if the testes produce testosterone, and if the cells of the genitals respond to the testosterone, the outer urogenital folds swell and fuse in the midline to produce the scrotum; the protuberance grows larger and straighter to form the penis; the inner urogenital swellings swell, wrap around the penis, and fuse in the midline to form the penile urethra.
If testosterone is not present, normal female development continues, with the development of a perineal urethra and the formation of a uterus, clitoris and vagina. ~ Wikipedia
This video is a bit cheesy. However, the information is helpful if you are not well versed in this area