sperm

Sperm count drop 'could make humans extinct'

Researchers assessing the results of nearly 200 studies say sperm counts among men from North America, Europe, Australia, and New Zealand, seem to have halved in less than 40 years.

Some experts are sceptical of the Human Reproduction Update findings.

But lead researcher Dr Hagai Levine said he was "very worried" about what might happen in the future.

The assessment, one of the largest ever undertaken, brings together the results of 185 studies between 1973 and 2011.

The world's strangest sperm

The egg meanwhile is the largest cell and similarly intricate. Looking further out into the natural world, the diversity of these sex cells, or gametes, is truly remarkable.

Most species have two gametes, which we term male and female.