Have any creatures ever developed ear “lids” to keep out unwelcome sounds? It would be such a blessing.

It would seem that the asker is unmarried. It is well documented that the mention of lawns, decorating, clothes and shopping can cause any husband to instantly develop them and all hearing channels will close.

Any future mention of beer, lager, football or pubs normally opens the lids and sound reception is restored as normal.
Brian Whittaker, Huddersfield

There’s a joke about a man who decides to redesign the human body to make it more consumer friendly. When it comes to the ears — rather ugly, stuck out there either side of the head — he decides to place them in the armpits.

Imagine, he explains, you’re listening to someone really interesting or funny, so you casually lean back in your chair and clasp your hands behind your head; if you’re bored, you just fold your arms defensively across your chest and all the boring noises are blocked out. Magic.
Huw Beynon, Llandeilo

How do woodpeckers avoid concussing themselves when they obsessively hammer away at tree trunks?

Several studies have examined the effect of drilling behaviour by woodpeckers and some lessons considered in relation to the prevention of head injury in man. Woodpeckers peck in order to identify cracks in trees, to drill for food, to make nests and to signal to each other. The woodpecker’s brain is obviously smaller than that of man and hence the ratio of brain weight to surface area is low and the deceleration force spread out more widely in the woodpecker. The space around the woodpecker brain is very small and the bone spongy so any impact to the brain is less than might be thought in relation to man’s rather larger subdural space.

The impact of the peck appears to be absorbed by muscles and ligaments in the head, and the force is transmitted largely through the base of the skull to the neck, bypassing the brain to some extent. Furthermore, a muscular sling around the head acts as a shock absorber.

The woodpecker pecks straight and so rotational forces, and hence shearing forces in the brain, are limited. Man might reduce the injury to his brain, when he can anticipate it, by tightening the neck muscles and holding the chin down.

Maybe some woodpeckers do suffer head and neck injury nevertheless!
Christopher Gardner-Thorpe, consultant neurologist, Exeter

My hair is now white. Why not then my eyebrows, which are still dark?

The stem cells at the base of hair follicles are responsible for producing melanocytes, the cells that produce and store pigment in hair and skin. The death of the melanocyte stem cells causes the onset of greying.