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Current Directions in Psychological Science.

It has been shown that the deeper the thrusting, the larger the semen displacement.

In the table, zero degrees is pointing straight up against the abdomen, 90 degrees is horizontal and pointing straight forward, while 180 degrees would be pointing straight down to the feet.

"Ejaculate quality, testes size and sperm competition in primates".

Efforts by scientists to are currently underway.

This is reflected in humans, as the sperm count in ejaculations is decreased if copulation occurs more than three to five times in a week.

Ejaculate adjustment One of the primary ways in which a male's ejaculate has evolved to overcome sperm competition is through the speed at which it travels.

is another form of alteration done to the penis.

Lateral cross section of the penis Parts• The human penis differs from , as it has no or erectile bone and instead relies entirely on engorgement with blood to reach its erect state.