My parents share their house with two female cats: Fluffy and Tippi. We've never shown much creativity when it comes to naming pets; Fluffy is long-haired, and Tippi is black with white feet. They are both probably well into feline dotage now, Tippi is 14 years old and Fluffy is only a year younger. They were introduced as adult cats, so they only tolerate each other's presence. They both stay outside most of the day, coming in only to investigate the chances of being fed. They are happy to sit on the verandah or deck watching, rather than chasing, the birds that land on the lawn.

What I find remarkable about the cats is that, of the four large mammals in our parents' house, they are by far the most competent.

Whereas my parents cannot tell the difference between cat food and breakfast cereal, the cats know without even having to look at it. Food that has gone off, food that reeks of decay, can often be found in the cupboards if we haven't dropped in on mum and dad for a few days. They can't smell it, and are at risk of eating it. The cats don't even sniff at it. They know what's good for them and what isn't.

After every meal, the cats sit on the deck and wash themselves. Fluffy has a particularly difficult job to do, as her fur is four or more inches long, yet she succeeds. Mum and dad have to be cajoled and manouevred into taking a shower.

The cats curl in a ball when they are cold, lie flat out on their back when hot. Mum and dad sometimes need to be told to put on or take off a sweater. Or dad will sit in the lounge in a singlet, with the heater going full bore.

Both Fluffy and Tippi conserve energy in a way that would evoke the admiration of any environmentalist but, when necessary, they can leap over a gate three or four times their own height, scamper up the outside steps, or jump onto the table to see what's being eaten. Mum and dad are increasingly unsteady on their feet. They've had several actual falls and many other close shaves with gravity.

I am quite sure, also, that if Fluffy and Tippi had all their human-operated support systems removed, they would go hungry for a while, but they would soon remember how to lie in wait for birds, how to cadge food at other back doors, and where the warm spots lie in other quiet back gardens. Fluffy once loved eating cockroaches. Maybe she would return with some nostalgia to the foods of her kittenhood.

Why are the cats so capable? They have brains that are a fraction of the size of our parents'. They get no assistance, especially not from each other. They cannot rely on lists, speed-dial telephone calls or frequent visitors to answer their questions. They just somehow get on with it. Of course, the human brain is adapted to far more complex tasks than those of a cat, and while it works it does these remarkably well. But why, when the cognitive faculties start to recede, do the basic survival skills recede along with the powers of abstraction, pattern recognition, social judgement, planning and aesthetics? Aren't we supposed to have a more primitive mammal brain lurking beneath our cortex, and an even more survival-focussed reptile brain encased within that? Why don't we just fall back onto their competence?

Is there something specific about human biology or longevity that renders us vulnerable to Alzheimer's, or is it suffered by other species? I wonder if there are any studies of old animal brains that show similar atrophy? Do the giant turtles, like Charles Darwin's Harriet, who died only three months ago at the age of 176 years, suffer from senility? If not, perhaps we ought to look at their neurochemistry for some clues.

I love our cats, but nowadays I also admire them.