Nothing adds more pleasure to a sunny spring evening than to stand at the window with a glass of decent burgundy and contemplate the gambolling of rinsed and blow-dried lambs.
There they go, bouncing in those spring-heeled leaps, tearing up and down the hill in a loose, woolly gang seeking a mound to play king of the castle. “Happiness is never better exhibited,” said Darwin, “than by young animals, such as puppies, kittens, lambs, &c, when playing together, like our own children.”
The list of wild creatures that appear to enjoy playing has expanded enormously with human observation. Charles Darwin was ready to accept an 1810 report of "ants chasing and pretending to bite each other, like so many puppies". And the real nature and significance of play and the study of animal behaviour (ethology) now feeds into the study of human behaviour (psychology) and the neuroscience of the brain.
With such rapid changes in human childhood, what play’s really about has never been more serious.
Aside from mock-butting of heads, lambs don’t go in for the rougher kinds of play – wrestling, hitting, biting – that many predatory animals engage in. That of lions, tigers or wolves can certainly look like a limbering up for later hunting as adults. But what should one make of otters taking turns to slide down a river bank, or an octopus using its water jet to bounce balls floating on the surface? Like the choughs I watch in updraught aerobatics, they all seem to have the sort of fun we ourselves could enjoy.
For the evolutionary biologist, play needs a purpose, a useful role in natural selection. If it didn’t it would simply disappear, they argue, since it takes up so much time and energy in early life. Perhaps it matters if the inventive, socialising, physical play of past generations (cowboys and indians, commando battles, street tag and so on) has been overtaken by solitary, sofa-bound zapping and elaborate virtual acquaintanceship. Childhood obesity, ready-made scenarios, monsters and heroes, inurement to violence – are all of these damaging the growth of the brain?
Science has already undone traditional understanding of some kinds of animal play. Rather like Darwin’s happiness, it projected our own pleasure to use words like “joyful” and “glad” about the singing of birds. We can still find it enjoyable, and even uplifting, while knowing that the song thrush is just staking out his territory.
Even the simple theory of play as rehearsal for later life has its problems. The pouncing and tumbling of lion and tiger cubs is not necessarily well-designed practice for actual hunting and killing. An experiment with Scottish kittens, for example, depriving one litter of toys to play with, found little difference in their later hunting skills.
In human evolution the manual kinds of life, for which old-style, more physical childhood play was a rehearsal, have greatly changed. Computer games foster and sharpen the mental skills the new world needs for survival, while sport and recreation now surely take care of the muscular.
An early theory of play was that it used up “surplus energy”. Now, in a housebound society haunted by paedophilia, are unused play urges piling up in the nervous system, a prompt for ADHD? Among small boys, it’s suggested, negotiated rough and tumble may be hard on adult nerves, but it is constructive physical and mental exercise in which real aggression plays small part.
Neuroscience is also taking a keen interest, as in the work of the American zoologist John Byers, of Idaho University. A student of the agile play of deer, antelopes and wild goats, he has rejected the idea of play as simply "getting into shape" not least because of its definite juvenile peak, falling off soon after puberty. This happens, too, in mice, rats and kittens.
It coincides, Byers points out, with the growth of the cerebellum, the part of the brain that co-ordinates fine muscle movements. Giving rats no one to play with when young has been shown to interfere with their brain development.
The broad and growing science of play still leaves room for every kind of question. Even the general consensus that play is an essential biological good has been challenged as a human invention. But even if the glow we feel when watching “playful” behaviour in other species is largely wishful thinking, I find no reason to disown it. And most of us will continue to see, in watching a kitten with a ball, the practice pouncing of cat upon mouse.
As for ourselves, while our cerebellum may, indeed, need physical childhood play for its refinement, I’ve seen little sign that the need for other kinds falls off with puberty. The whole electronics industry must certainly hope it does not.