The idea that sperm “race” to the egg has been debunked. According to experts, the process is more complex than a simple swim meet. The key player in fertilization is actually the female reproductive tract.
Sperm do swim towards the egg, but it’s not their movement alone that propels them forward. Contractions of the uterus and other parts of the tract also play a crucial role. In fact, scientists have found that sperm can travel at speeds of up to 5 millimeters per second within minutes.
However, the egg itself doesn’t swim. Instead, tiny hairs called cilia help it move towards the fallopian tubes where fertilization takes place. This means that the sperm and egg are moving in opposite directions, creating a current that the sperm must overcome.
The female reproductive tract is also selecting for healthy sperm throughout the process. Sperm that get too close to the sides of the tract may stick and lose their momentum, while those that bind to the wall receive metabolic benefits that increase their lifespan.
Even though the sperm that arrive first are often considered the winners, they still need time to mature before they can fertilize the egg. The female reproductive tract is constantly evaluating and selecting for the best candidate, making the process more like a job interview than a competition.
Source: https://www.livescience.com/health/sex/do-sperm-really-race-to-the-egg