Katie, of Sawston Village College, asks :-

Does a tiger have different organs to a snake?

Alex Davies, an anatomist at Massey University's Institute of Veterinary, Animal and Biomedical Sciences, responded.

Tigers and snakes are both feared and worshipped around the world. They have an unpredictable relationship with humans. But while they seem so obviously different in having legs or not, or in having hair or scales, are they so different beneath the skin?

In relation to the extreme forms of life on earth, their organs are remarkably similar. Animals with backbones appeared in the fossil record 500 million years ago. The common ancestor of snakes and tigers left its life in water to breed on land about 350 million years ago. It had to have all the necessary equipment for this kind of life. Compared with the adventure up to this stage, the differences needed for life as a tiger or as a snake are relatively small.

Some snakes lay eggs and others give birth to young in the way that tigers do. Unlike fish and frogs, who lay eggs in water, the eggs of both snakes and tigers must be fertilised internally, so they have organs to do this, just as they must have an organ within the female to either form an egg shell or nurture the growing fetus. Both snakes and tigers have lungs, and fill them with air by moving the body wall, although snakes have no diaphragm to help. The kidneys of snakes produce only a little volume of urine and while other reptiles have bladders, snakes do not need to store urine. Also, urine, food waste and eggs all leave a snake's body through a common opening, while tigers separate the food waste.

Some differences between snakes and tigers may be considered due to different evolutionary paths. Examples are the structure of the jaws and teeth, the degree of division of blood as it is pumped through the heart, and the special parts of the brain. But mostly, the organs of snakes and tigers are no more different in appearance than those of a tiger and, say, a sheep are different.

In the end, what do we learn from most - understanding the similarities or understanding the differences? Some people are "lumpers" and some are "splitters". What would you prefer to be?