Some animals lay eggs, and their young hatch out of them. Other animals give birth to live young. But which strategy is best?

That’s the question that’s been bothering CrowdScience listener Sameer in Canada. Is giving birth to live young a good reproductive strategy? It takes a lot of time and effort, and it doesn’t result in that many offspring. Egg-laying, on the other hand, allows you to produce lots of young at one time to maximise the chance of survival, seems easier than giving birth, and you can lay eggs more often. So why have humans and most other mammals evolved to give birth to live young?

To find the answer, presenter Anand Jagatia travels way back into the past with Paul Barrat from London’s Natural History Museum in the UK to look at the evolutionary history and advantages of egg-laying. What have gravity and moisture got to do with the success of an egg?

Palaeontologist Kimi Chapelle from Stony Brook University in the US shows Anand the oldest eggs ever found, and we discover why even older eggs are missing from the fossil record.

We discover how the evolution from egg-laying to birth-giving is happening right in front of our eyes, with Camilla Whittington from the University of Sydney, Australia. And we might even have an answer to the age-old question about eggs - which came first?

You can see the oldest eggs ever found here: https://www.nhm.ac.uk/discover/news/2020/april/most-detailed-look-inside-worlds-oldest-dinosaur-eggs.html

(Photo: A chick hatching from egg on egg tray. Credit: David Malan/Getty Images)

Presenter: Anand Jagatia

Producer: Margaret Sessa-Hawkins

Editor: Ben Motley