Interesting Study:

Three Ontario Universities were commissioned by the government to discover why the human penis is the shaped the way it is.

U of T allocated a budget of $500,000 for research. After 2 years they concluded that the reason the head of the penis is wider than the shaft is that it fits better, when in situ, so to speak. This would prevent leakage of semen and increase the probability of successful fertilization.

McMaster University spent $750,000 on a research program that lasted 3 years. The results showed that the penis widened near the tip because it maximized the number of nerve endings stimulated during sex. This would lead to increased sensitivity and a better chance of impregnation.

Finally, York University spent $2.50 on a copy of Playboy and 10 minutes in the staff toilet, only to discover that the penis widens at the tip in order to prevent your hand from slipping off the end.