This month, India began the immense undertaking of surveying its population of 1.4 billion people in the world’s largest ever census. Inspired by this huge task, the Unexpected Elements team explores some population science.

First, counting – or miscounting – populations. The global human population may be much larger than previously thought as research shows counts may have missed those living in more remote areas. And we learn about the species stuck in a neverending “species limbo”, where they’ve gone unseen for decades but still can’t officially be declared extinct.

Next, we’re joined by geneticist Dr Ambroise Wonkam, one of the researchers behind the Three Million African Genomes project, who tells us why sequencing more African genomes is the key to unlocking a wealth of vital genetics knowledge.

Also, Mumbai’s out of tune musical road, how we know volcanoes are extinct, and the weight of the internet.

All that, plus many more unexpected elements.

Presenter: Caroline Steel, with Chhavi Sachdev and Candice Bailey.