Watch these sperm wriggle up a model reproductive tract

When it comes to sperm, only the fiercest swimmers can wriggle past the bottlenecks of the female reproductive tract, new research shows. The study could help one day improve tests for male fertility. But, in the meantime, it brings us delightful footage of sperm desperately, fruitlessly swimming into a fake fallopian tube. Sorry, little guys.With a single ejaculate, 100 million sperm can swim up the female reproductive tract — and the theory goes that only solid swimmers can make it to t