The scientists who conducted the research placed healthy sperms under a laptop running a Wi-Fi connection.
After four hours, the Wi-Fi exposed sperms showed "a significant decrease in progressive sperm motility and an increase in sperm DNA fragmentation" compared to healthy sperms stored for the same time in the same temperature away from the computer.
That is, the sperms exposed to Wi-Fi were less capable of moving towards an egg to fertilize it and less capable of passing on the male's DNA if it does fertilize an egg.
The scientists blamed the damage on non-thermal electromagnetic radiation generated by the Wi-Fi."
Link to Original Source