Hundreds of thousands of years of evolution have adapted our bodies to life on Earth. But the pace of technological and social change has exposed our frailties. Time for a rethink?

Imagine being able to drink until your liver packed up, knowing that you had another to take the strain. Or never mis-typing words on your BlackBerry because of your narrow fingertips specially designed for tiny keyboards.

Welcome to the human body, mark II, dreamt up by specialists who believe that nature's work can be improved upon. They argue that our bodies are riddled with design errors which remain uncorrected despite millennia of evolution.

From our upright posture, which puts excessive strain on the knees and hips, to our morbid, year-round interest in sex, a number of anatomical and hormonal alterations are now overdue, doctors say.

They range from switching the location of the genitals from the groin to the armpit, in order to put them at a hygienic distance from the excretory organs, to adding a back up heart and liver to cope with the rigours of the modern diet.

Detachable body parts and an annual mating season, timed to avoid clashing with major sports events, have also been proposed.

Writing in the British Medical Journal, Paul Brown, a US consultant in prion diseases, summarises his ideas in a sketch in the style of Leonardo Da Vinci. He spells them out in a "Letter to God" which gently berates the Creator.

"Our perversity in wanting to walk upright, when it is clear that this was not Your intention, has led to some real problems with our spines and leg joints. Would it be possible for you either to fix the pelvis at a right angle to prevent us from this error, or to strengthen our weight-bearing joints?"

Modifications to suit a 21st century lifestyle ought to include tiny fingertips for operating portable e-mail devices, and a back-up liver to cope with the prodigious quantities of alcohol now routinely imbibed. "You probably did not intend us to discard our diet of berries and nuts for fatty meats and pastries but that is what happened, with disastrous consequences to our cardiovascular systems. Two hearts and a lipid-resistant lining to blood vessels would be just the thing," he writes.

Transforming our fat-laden cuisine to harmless molecules with a new enzyme would achieve the same objective. But to satisfy puritans on alcohol, an alternative strategy would be to alter our metabolism so it makes us too sick to consume it - and all the other drugs of addiction.

The close proximity of the genitals and excretory organs may be intended to remind us of original sin, Dr Brown contends, but it would be more practical if the genitals were re-located elsewhere, perhaps employing "some kind of retractable underarm mechanism".

Some rebalancing is also necessary between the "pleasures of sex and the pain of reproduction". With low rates of infant mortality in the Western world it ought to be sufficient to provide each woman with only two or three eggs to reproduce. That would also spare them "an endless succession of menstrual periods and the hot flushes of the menopause".

Similar improvements to the human anatomy were proposed a decade ago in BMJ by doctors and celebrities. They included a mating season around the winter solstice and a breeding season in the autumn - timed to avoid clashing with rugby internationals. This not only releases women from "totally unnecessary" monthly ovulation but also liberates both genders from their obsessive, year-round interest in sex. "If male aggression were confined to a short rutting season the benefits would be incalculable," one contributor said.

Jo Brand, the ample comedienne, called for the average female statistics to be rewritten as 96-90-96 "thus making me the Kate Moss of Jurassic Park". She also suggested speeding up the ageing process "so that people were forced to pack as much into a short life as possible rather than constantly looking to the future to fulfil their dreams".

Arthur Smith, the writer and stand-up comic, suggested detachable male genitals which could be put in a drawer and kept at home when not needed "so there is nothing banging about between the legs when playing football".

He also proposed detachable limbs, to make cuddling easier, and to allow others to buy you clothes. "You could send your legs off with a friend to buy trousers while you sit on your torso and watch the telly."

Correspondents to the current issue of BMJ offer additional modifications. Kenneth Campbell, of the Leukaemia Research Fund, says six fingers on each hand would result in the creation of a base 12 numeric system - with considerable advantages. "Just think of the convenience - 12 is exactly divisible by 2, 3, 4 and 6 whereas 10 is divisible by only 2 and 5."

Dominic Horne, a GP, proposes separating the pipework for swallowing and breathing to reduce the risk of choking, while Andy Wood, an ophthalmologist, spots design flaws in the eye.

But for the ageing human, Kirti Kain, of the University of Leeds, suggests that the increase in body hair and the decrease in hair on the scalp could be exchanged.

A body of improvements

* Remove tonsils

In theory, these flaps of lymphatic tissue found on either side of the throat help the immune system to fight infection in the body. In reality they are of little use, except perhaps in keeping surgeons in business taking them out.

* Fill in sinuses

The paranasal sinuses are cavities above and behind the nose. Though they lighten the skull and add resonance to the voice, all they ever really do is get infected. Bad news for the body, but good news for the makers of remedies like Sudafed.

* Strengthen neck muscles

Necessary if sinuses are to be filled in. A heavier head is a small price to pay for freedom from infection. But a thicker, more muscular neck might render existing shirts too tight around the collar.

* Make fingertips smaller

Nothing is more frustrating than trying to send e-mails on your Blackberry with fat, stubby fingers. Refinement is overdue. Could, however, lead to a rash of unsolved crimes as smaller fingers pose problems for police fingerprint experts.

* Add spare liver

Everyone loves to believe that drinking red wine is good for you. The sad fact is that the existing one can't cope with the amount of partying modern lifestyles require. A second one would increase endurance.

* Relocate genitals and make retractable

Heaven for armpit fetishists. Their current location is puzzling, close to the organs of excretion and vulnerable to flying objects. Could make applying deodorant problematic - especially in public.

* Strengthen knee and hip joints

The current ones are not up to the job of walking upright. Alternatively, fix the pelvis at a right angle, so we walk on all fours. Could prove popular with people who like to buy shoes.

* Remove appendix

It is useless and only comes to notice when infected. Trainee surgeons will have to find another operation to practise their skills on. But what of the Pakistani man who holds the world record for the longest appendix? (It measured 9.2in.)

* Add spare heart

One heart was fine when we browsed the fields for nuts and berries. Now we have switched to burgers and doughnuts, two would be good. Perhaps the spare one could be worn on the sleeve.