Why don't Animals Crossbreed?

Can we eliminate flies and mosquitoes from our ecosystem and live in peace? When will the universe end? Do eggs with double yolks mean that two twins would have been born? Why don't animals such as lions and zebras cross-breed? Why is it best for women to have babies when they are younger? Does the direction that the water goes down a plug-hole change if you are in the Northern or Southern hemisphere? Is it possible to overcome a fear? Plus, news of a new discovery that bugs in your gut may be able to keep you healthier at old age. Chris Smith answers your questions with Eusebius McKaiser on... Like this podcast? Please help us by supporting the Naked Scientists