Chris - Best estimate I know, Bill, is we think there are 1.37 billion cubic km of water on Earth!

Chris - It’s the same reflex if you need to roll over in bed when you’re uncomfortable.  If you stayed in one position in bed all the time all night you would get a pressure sore because the pressure of tissue against the bed would stop blood flow through that area.  As a result you would end up with a de-vascularised bit of skin and it would necrose.  Patients who are left in one position in hospital for too long get exactly the same problem.  The body has a series of reflexes programmed into it even when you are asleep.  You can react and respond to various stimuli with an appropriate thing.  If you’re getting uncomfortable in bed you can roll over.  If, on the other hand, your bladder’s getting full then your brain says wake up, you need to go to the loo.  It’s an automatic reflex.  Some people lose that reflex as they get older.  Some people when they’re very little actually wet the bed because it hasn’t developed yet.  That’s why little kiddies have to respond to those signals the right way.  That’s all about potty training and bladder training.

Robert - Symmetry is good but it isn’t always good.  Like everything else in evolution when selection is strong enough it will change things.  The benefits of being able to see for a flounder clearly outweight the benefits of symmetry and so evolution has shaped it.  It yet again shows there are many different ways of surviving and reproducing in nature.

Robert - Well not directly.  Fortunately we don’t all come with genetic labels on our faces like barcodes but we do know that our facial structure’s like everything else, strongly under genetic control.  What we also know is people are extraordinarily good at recognising faces.  We can pick faces out or very complex backgrounds and that is enormously important for us to be able to separate individuals out.  The answer’s almost certainly yes.  It’s one of the best things we’re at.  Of course, we can do it between individuals and very easily between populations.