The tail of a human spermatozoid sways only one way when swimming. To go in a straight line, the head turns round, according to a study by scientists who published this Friday in the scientific journal Science Advances .

Dutch microbiologist Antoni van Leeuwenhoek saw moving animals in human sperm through his homemade microscope in 1677. He saw that sperm cells moved in a symmetrical pattern as the whip tail moved back and forth.

Scientists from the University of Bristol have taken high-speed images of free-swimming sperm cells with a special 3D microscope. This shows that the tail sways only one way, and that the head then turns, causing the sperm to 'drill' through liquid like a corkscrew. If the head didn't rotate, the sperm cells would swim in a circle.

The new discovery could be a major step in infertility research, a specialist told the science website Science News. Further research remains to be done to determine whether the spermatozoid movements now observed also occur in the female reproductive organ.