If we look across the whole of the mammal branch of the tree of life, we find there are many groups of mammals that have evolved testicles of all different sizes. In almost all these separate cases, ...

Ziya Tong had her home, food and body tested for microplastics while working on a documentary on the subject. ‘Making the film Plastic People made me realize I am a human landfill,’ she writes.

The human chin has been fertile ground for arguments between scientists over its purpose. As with testicles, there are half a dozen plausible ideas to explain the evolution of the human chin.