Women of child-bearing age steadily run out of eggs by the continuous process of cell death. While reading a copy of the Guardian carefully from cover to cover, a normal woman will have lost on average two eggs - while, typically, a normal man will have made 70,000 new sperm.

Both in Britain and America, huge publicity has been given to stem cells, particularly embryonic stem cells, and the potential they offer. Of course, the study of stem cells is one of the most exciting areas in biology, but I think it is unlikely that embryonic stem cells are likely to be useful in healthcare for a long time.

I don't believe the fertilised egg can be equated with the sort of human life that you and I represent, or our children represent.

When I grew up, we didn't have a TV, and I think more families today have ambitions of getting out of their environment, such as sending their children to university.

We live longer and healthier lives than ever before. Animal research has improved the treatment of infections, helped with immunisation, improved cancer treatment and had a big impact on managing heart disease, brain disorders, arthritis and transplantation.

The trouble with climate change is it's an extraordinarily diverse and complex issue, but for example if the BBC would let me make some of the programmes I'd like to make on climate change, I bet you there would be a change of emphasis.

In prehistoric times, Homo sapiens was deeply endangered. Early humans were less fleet of foot, with fewer natural weapons and less well-honed senses than all the predators that threatened them. Moreover, they were hampered in their movements by the need to protect their uniquely immature young - juicy meals for any hungry beast.