Female factors can influence the result of sperm competition through a process known as "sperm choice". Sperm competition is often compared to having tickets in a raffle ; a male has a better chance of winning i. Males have been found to make the most sperm in species where individuals are most promiscuous. Offensive adaptation behavior differs from defensive behavior because it involves an attempt to ruin the chances of another male's opportunity in succeeding in copulation by engaging in an act that tries to terminate the fertilization success of the previous male. This has also come under some criticism; see Cervix Function.
Other studies have found no connection to sperm transport or fertility.
In some species, penises are specifically shaped to pack sperm tightly into the corners of the female reproductive tract, whereas others are armed with spines, brushes, barbs or hooks to scrape out the sperm of previous males, or stimulate the females to release sperm. Numerous inbreeding avoidance mechanisms operating prior to mating have been described. This encourages the males that are watching to attempt to mate with the non-preferred female. Males who have successfully courted a potential mate will attempt to keep them out of sight of other males before copulation. What goes in must come out.