FAMILIES DON'T NEED FATHERS

Male animals can't give birth or breast-feed, and won't care adequately for their young. What is the point of them? On Father's Day, Sanjida O'Connell finds it hard to say

What use are males? Apart from providing sperm, most male animals don't give birth, don't breast-feed their babies, don't cuddle them, carry them, baby-sit them and may even kill them if they suspect they are not their own. Male parental care is rare in invertebrates and uncommon in mammals.

Are male animals really lousy fathers? Paternal care is frequent in fish and nearly universal in birds, but are avian fathers any better or even as good as their female counterparts? Biologists have shown that there are very good biological reasons for male care or lack of it: if a male can desert his family for opportunities to mate with other females, he will - and lack of male care for youngsters stems from many a male's deep- rooted insecurity that he is not the father.

The root of the problem stems from a very basic fact: males have sperm and females produce eggs. It may not seem such a big difference, but it results in a great disparity between male and female behaviour. Female investment in the larger eggs (and in mammals, pregnancy) means that the female strategy is to concentrate on rearing a few youngsters, whereas an abundance of sperm (a healthy man, for instance, can produce 300 million sperm in one day) results in the well-known male strategy of attempting to inseminate as many females as possible.

To make up for this initial shortfall, some males invest in their future offspring even before copulation by feeding the female. Several families of insects wrap their sperm in a nutritious protein membrane which the female eats. Other males bring the female prey - this has an added advantage: the larger the prey, the longer the male is allowed to copulate while the female is eating his nuptial gift. Male spiders make the ultimate sacrifice, frequently ending up as a post-coital snack (thereby providing the female with extra nutrients for her eggs).

But the crucial determinant of whether a male will look after his offspring is how certain he is of their paternity. When fertilization is external, males have a very good idea of whether the offspring are theirs and so are more likely to care for them. Male cichlid fish scrape a shallow basin in the sand with their noses and invite females to spawn. As they do so, the male scatters his sperm over the eggs. A female will try and eat her own eggs. If a male chases her away vigorously, she knows she has left them in good hands; if he doesn't, by eating her eggs she can recycle the nutrients into a new batch.

The male aerates the eggs, picks out parasitised ones, and protects both eggs and hatchlings. He cares for the eggs certain that they are his own, and is still able to mate with a number of females who visit his spawning site. Unfortunately for the males of some species of fish, there is often a second type of male who pursues a sneaky strategy. These are smaller than normal males, and mimic females, which allows them to dart in and inseminate the eggs without having to look after them.

Males are far less likely to care for infants in any major way when fertilization is internal because they have no guarantee that the infants are their own. In mammalian species where the female has a long pregnancy and male uncertainty is high, male care is rare. Male birds help feed their chicks but they have a far greater degree of paternity certainty for two reasons. The first is that 90 per cent of birds are monogamous - so, all things being equal, he can assume the fledglings are his. The second reason why male birds care is that gestation is very short: only a few days elapse between mating and egg- laying, and during this period the male keeps tight surveillance on his partner.

Bank swallows, for example, stay within a metre of their mates, and accompany them on up to 100 foraging trips a day. Once the female is no longer fertile, the male chases other females in the hope that their mate's guard will slip. And male care can cease as quickly as it began: male swallows abandon the nest and youngsters if the female is caught fraternising with another male.

Males will go to extraordinary lengths to make sure they are not cuckolded. Unusually for an insect, male water bugs care for their young - by brooding them on their back. Fertilization is internal, and the female can retain another male's sperm for up to a month - so strenuous mate-guarding has little effect. The water bug's strategy is to try and flood the female with his sperm: during mating she is only allowed to lay about three eggs before he mates with her again. On average, females lay 150 eggs in 36 hours during which time she will have undergone 100 copulations.

The mode of fertilization - whether internal or external - determines which sex is able to desert the nest or den first. Biologists believe the animal motto is "If you can, go". External fertilization allows females to desert first, as in the cichlid fish where the female dumps her eggs on the male, but when fertilization is internal, the male has a much better chance of mating again than the female. This applies even in species where males are traditionally supposed to care. In monogamous species with bi- parental care, the amount of investment each member of a pair contributes depends on what his or her partner is doing. For instance, in starlings, if one member of the pair is not pulling his or her weight, the other will compensate for the shortfall. Even so, females tend to compensate more than males. The much larger female investment in laying and brooding the eggs makes her less inclined to abandon the whole lot even if the male deserts her.

Males, on the other hand, are quite capable of pursuing other options. Because copulations for the male are so inexpensive, males will often pursue a mixed strategy, caring when they have to, and mating with other females when the opportunity arises. The famous animal behaviourist, Konrad Lorenz, was incredibly disappointed when he found his beloved geese were unfaithful. Although geese, like many birds, pair for life, they are not averse to extra-pair affairs.

The mating system of French accentors, small birds that live in the Pyrenees, is complex, consisting of several females and males all cohabiting on one territory; it's also a microcosm of male and female strategies for parental care. Females are capable of rearing their nestlings by themselves, but male help is an added bonus ensuring that the chicks will weigh more and be healthier when fledged. Males can't tell which chicks are theirs, so they help the females according to how much time they spent with each one prior to egg-laying. However, given a chance, male investment in this species veers towards mating rather than feeding.

Because the females are not in season all at once, there are times when the chicks a male is likely to have fathered will need to be fed. At other times, fertile females will present fresh opportunities for mating. A nest may receive no help from any of the males because other females are fertile; then, several males may help raise chicks from one nest while the rest of the females are incubating eggs. However, a female will only gain the help of all the males on the territory if she has mated with all of them and they are not distracted by mating or broods belonging to other females .

The environment also plays a determining role in what kind of mating system a species will adopt and hence what kind of care a male will give. Harshness encourages male help because otherwise the young would not survive. For example, in the Arctic there is only a short season of food abundance. Females are not limited in the amount of eggs they can lay, so sanderling and spotted sandpiper females mate with two males, one of whom looks after one clutch while she looks after the other.

Certainly in mammals few families have evolved male care. Those that have tend to rely on the male to care for the young indirectly by defending a territory or warding off predators or other marauding males. Given the fact that mammals are internal fertilizers and females have comparatively long pregnancies and reliant young, male investment would seem a non-starter. But even here evolution has some surprises - biologists have discovered that one type of male, the dyak bat, produces milk. But so far no one has seen a male breast-feeding.

! Sanjida O'Connell's first novel, 'Theory of Mind', will be published on 11 July by Black Swan at pounds 5.99.