Garden snails are evolving slower metabolisms.

Natural selection is favouring snails with reduced metabolic rates, researchers in Chile have discovered.

It is the first time that evolution has been shown to select for this trait in individuals of any species.

Snails with lower metabolisms are at an advantage because they have more energy to spend on other activities such as growth or reproduction, the researchers say in the journal Evolution.

Anyone who admires the tolerance and sexual freedom enjoyed in Spain today may see this as a reaction to the extreme sexual micromanagement imposed upon Spanish women during the Franco years.

"If your husband asks you for unusual sexual practices, be obedient and don't complain. If he suggests union, agree humbly? When the culminating moment arrives, a small whimper on your part is sufficient to indicate any pleasure that might have been experienced."

Such conjugal advice formed part of a battery of intimate instructions imposed upon millions of Spanish women for 40 years by the Feminine Section of the fascist Falange group, now explored in an exhibition about those who joined its blue-shirted ranks. The all-powerful Seccion Femenina also dictated how women should behave at work, to the point of eliminating expression altogether.