The Difficult Choice of Being the First Heart Donor

For a dying man it is not a difficult decision [to agree to become the world's first heart transplant] ... because he knows he is at the end. If a lion chases you to the bank of a river filled with crocodiles, you will leap into the water convinced you have a chance to swim to the other side. But you would not accept such odds if there were no lion.

 Species Divisions are Complicated

Zoologists have traditionally divided the vertebrates into classes: major divisions with names like mammals, birds, reptiles and amphibians. Some zoologists, called 'cladists',* insist that a proper class must consist of animals all of whom share a common ancestor which belonged to that class and which has no descendants outside that group. The birds would be an example of a good class. All birds are descended from a single ancestor that would also have been called a bird and would have sha...