Is there any evolutionary advantage in snoring?

Also in this week's column:

• The Minamata disaster - 50 years on
• What is deep vein thrombosis?
• Can leaving a baby to 'cry it out' cause brain damage?

Is there any evolutionary advantage in snoring?

Asked by John Edwards of Hitchin, United Kingdom

We have addressed snoring many times in many ways.

Points we have not made so far about snoring include:

1. The reason that we snore more in old age is that the throat muscles involved in preventing snoring become somewhat weaker and more flaccid with age.
2. Fatter people tend to snore more because fat deposits accumulate in the tissues of the airways. This makes the tissues heavier and causes the tissues to block more of the normal line of airflow.
3. An estimated 45 per cent of people snore from time to time and 25 per cent are habitual snorers.
4. You snore more when sleeping on your back because in that sleep position gravity causes the tongue to fall backwards somewhat. This can narrow the airways and partially block airflow.

What we have not answered is the puzzling question of what could be the evolutionary advantage in making a sound while snoring? Making noises (often very loud ones) while sleeping would seem only to advertise the fact that one is sleeping - and thus being more vulnerable to harm from other humans and predation for other animals.

Making a sound while snoring would seem to provide no advantage and at least one definite disadvantage for survival. So how has this noisy behaviour survived natural selection?