R W Carden's suggestion (Opinion, March 28) that intelligence is a product of a meat-based diet is an interesting theory.

However, there are several herbivore species, for example elephants and gorillas, which are more advanced socially and intellectually than most primary carnivores, for example lions.

The evolution of the animal mind is far more complex than simply being a product of diet.

For most animal species, the most important essential for success was to grow to maturity and independence as quickly as possible with the least possible cost in food and energy.

At a very late stage in evolution, the primates reversed this process and slowed down the growth rate of their young and lengthened the period of dependence on their parents.

It was this step that allowed the development of mind and intelligence.

Although this is a very simplistic summary of a complex process, as a general rule, the longer the maturation and dependence process, the more intelligent the animal.

The cultivation of fields and the keeping of livestock freed the human animal from the need to constantly search for food.

-Frank Prince-Iles, Sunnydale Avenue, Brighton