66 million years ago, a huge asteroid hit the earth, wiping out most of the dinosaurs that roamed the land. It would still be tens of millions of years before the first humans appeared - but what if those dinosaurs hadn’t died out? Would we ever have evolved?

CrowdScience listener Sunil was struck by this thought as he passed a Jurassic fossil site: if dinosaurs were still around, would I be here now?

We dive back into the past to see how our distant mammal ancestors managed to live alongside huge, fierce dinosaurs; and why the disappearance of those dinosaurs was great news for mammals. They invaded the spaces left behind, biodiversity flourished, and that led – eventually – to humans evolving. It looks like our existence depends on that big dinosaur extinction.

But we explore a big ‘what if?’: if the asteroid hadn’t hit, could our primate ancestors still have found a niche – somewhere, somehow - to evolve into humans? Or would evolution have taken a radically different path: would dinosaurs have developed human levels of intelligence? Is highly intelligent life inevitable, if you give it long enough to develop? We look to modern day birds - descendants of certain small dinosaurs who survived the asteroid strike - to glean some clues.

With artist Memo Kosemen, palaeontologists Elsa Panciroli and Darren Naish, palaeobiologist Anjali Goswami, and Professor of Comparative Cognition Nicola Clayton

Presented by Marnie Chesterton and Anand Jagatia

Produced by Cathy Edwards for the BBC World Service

(Photo: Silhouette of people and Dino. Credit: Getty Images)