They believe humans shouldn't have children. Who are the anti-natalists - and how far are they willing to push their ideas?

"Wouldn't it just be better to blow a hole in the side of the earth and just have done with everything?"

Thomas, 29, lives in the east of England, and although his idea of blowing up the world is something of a thought experiment, he is certain about one thing - humans should not have babies, and our species should gradually go extinct.

It's a philosophy called anti-natalism. While the idea dates back to ancient Greece, it has recently been given a huge boost by social media.

On Facebook and Reddit, there are dozens of anti-natalist groups, some with thousands of members. On Reddit, r/antinatalism has nearly 35,000 members, while just one of the dozens of Facebook groups with an anti-natalist theme has more than 6,000.

They are scattered around the world and have a variety of reasons for their beliefs. Among them are concerns about genetic inheritance, not wanting children to suffer, the concept of consent, and worries about overpopulation and the environment.

But they are united in their desire to stop human procreation. And although they are a fringe movement, some of their views, particularly on the state of the earth, are increasingly creeping into mainstream discussion.

While not an anti-natalist, the Duke of Sussex recently said he and his wife were planning to have a maximum of two children, because of environmental concerns.