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Family matters

Question: My observations suggest that in Britain there are clusters of mole colonies with large mole-free regions in-between. How did distant colonies get started? Is each colony hopelessly inbred? Are moles a British phenomenon? Or are there similar continental moles and, if so, how did their communities spread?

Moles are not purely a British phenomenon. There are 30 species worldwide, seven of which are found in north America. Most moles spend the majority of their lives underground in a system of permanent and temporary tunnels. Exceptions are the desmans, which are aquatic, the star-nosed mole, which is semi-aquatic, and the diminutive shrew-moles that forage underground and on the surface.

Moles may burrow as fast as one foot per minute. Their surface tunnels are usually only temporary and appear in newly cultivated fields, in areas with light, sandy soil and in very shallow soils where prey is concentrated just below the surface. More usual is a permanent system of deep burrows that can form complex networks hundreds of metres long at varying depths. The deepest tunnels are used most during periods of drought and severe cold. Permanent tunnels are used repeatedly over long periods of time for feeding, sometimes by several generations of moles.

The mole Talpa europaea is found very widely throughout Britain (but not in Ireland), and occurs in every county on the British mainland. Individuals are solitary for most of the year, occupying separate territories and rarely exceeding a density of three per acre. They only live in places where the soil is suitable for feeding and for tunnelling, and all mole species prefer moist soils where burrowing is easy. They are rare in coniferous forests, on moorlands and in sand dunes, probably because food is scarce in these areas.

Little is known about populations and the demography of moles nor the size of their home ranges. However, studies suggest that the home ranges of moles may be substantially larger than those of other burrowing mammals. Adult moles have been known to move up to 1500 metres.

At the start of the breeding season, males enlarge their territories, tunnelling over large areas in search of females. The young start to leave the nest at 33 days and disperse from the mother’s range at about six weeks. The young travel overground until they find a suitable new habitat, and this dispersal is a time of great danger. It is thought they may travel up to a few kilometres, which may explain how distant colonies get started. A survey conducted in the Netherlands suggested that moles could colonise land at a rate of up to three kilometres a year. They can also swim across 600 metres or more of open water.

Based on the distances males are thought to travel, inbreeding would not be common. The isolated patches you observe are probably far less isolated than they appear. And a lack of molehills does not necessarily indicate a lack of mole activity, because areas with established tunnels may not require as much hill-making as virgin territory, and hills are not as noticeable in forests and hedgerows, say.

If large mole-free areas really do exist, this is most probably due to humans changing the character of the intervening or surrounding land, or killing the resident moles, and such patches are likely to be a relatively recent phenoenon—Ed

With thanks to Matthew Mason, Department of Zoology, University of Cambridge

Red rain

Question: What is the evolutionary significance of red hair? Here in Northern Ireland, it’s a lot more common than in most countries I’ve visited and, as it’s usually pretty overcast, redheads don’t suffer the skin reactions they often experience in sunny climes.

Is red hair an evolutionary adaptation to damp, dull climates or is this just the only kind of place redheads can live comfortably?

Answer: Red hair in humans is associated with a loss of function in the melanocortin 1 receptor gene. The ancestral, fully functional version of the gene produces dark pigment, but a person with two copies of a dysfunctional variant will produce the lighter pigment that results in red hair, pale skin and freckling.

It has been suggested that pale-skinned people may have an evolutionary advantage in some climates. The skin synthesises vitamin D on exposure to sunlight, and in countries where there is limited sunlight, lighter skin pigments that allow greater penetration of ultraviolet rays may help prevent vitamin D deficiency. Because pale skin is associated with red hair, it was thought this could explain why redheads are prevalent in the perennially overcast Celtic countries.

However, recent studies have found no evidence for this. Instead it seems that while the redhead gene confers no particular advantage, there is a positive selection pressure for dark hair. And associated dark skin types are selected for in sun-drenched regions, due to the protection they afford from skin cancer. When this selective pressure is relaxed, as it is in northern Europe, variant genes appear. As these genes have neutral selectivity they drift through the population, producing a small proportion of redheads.

This doesn’t not explain local differences in the frequency of red hair, however, though it may simply be that some cultures find red hair more sexually attractive than others. The secret may finally be revealed by studies that are now investigating why red hair seems to be more prevalent in Ireland and Scotland compared with their close neighbour, England.

Darren Logan

MRC Genetics Unit Western General Hospital, Edinburgh

Nailing it

Question: Why are the ends of your fingernails white, and why is there also a whitish semicircle where the nail joins the finger?

Answer: The nail is translucent and essentially colourless, but it appears pink because of blood vessels under it. The cells of the nail consist primarily of keratin and are bound to each other by protein fibres. They form at the root of the nail and broaden and flatten as they move towards the fingertip.

The half-moon shaped area visible at the base of the nail is also called the lunula. This pale area is comprised of unkeratinised nail cells that are not matured nor flattened out. As these cells grow forward they become flat, hard and transparent.

The characteristic white colour of the nail’s free edge is due to the fact that the top layer of the skin underneath the fingernail is attached to the underside of the nail and the cells remain stuck to it as it grows out.

Johan Uys

Bellville, South Africa

This week’s question

It’s nuts: Peanut allergy is increasingly common, and children have been known to die after eating peanuts. Why is it becoming more widespread and, more importantly, how can peanuts kill someone?

Patrick Shackleton

Dubrovnik, Croatia