In the five years before she died, my elder sister Susan was plagued by shortness of breath. For Ann, the dominant last symptom was pain. For Mike, whose recent operation has made all the difference, it was ankle swelling. Odd as it may sound, all suffered unnecessarily because their bodies responded inappropriately to their illness. Three times Mother Nature got it wrong; three times serious limitations of evolution were revealed.

Darwin’s theory of evolution, which was one of society’s great demystifiers, makes perfect sense. Because there have always been small differences between individuals, even amongst the tiniest of living forms, some will be better able than others to cope with, or take advantage of, environmental challenges. Since many of the differences are transmitted from one generation to the next, when changes accumulate those that are more successful break away to form new species. In each instance, selection is driven by Darwin’s ‘survival of the fittest’.

But in this process there is an important limitation. The advances in evolution only play on selection that occurs up to the successful production of the next generation. The ‘parent’ can then die, and with life expectancy amongst Homo sapiens in those early days of the order of 35 years, that is what adults did. Accordingly, evolution never selected for improvements in older individuals, and it is often then that Nature begins to let us down.

In keeping, Susan, Ann and Mike faced problems when they were long past their reproductive age. My sister’s shortness of breath started after a heart attack. Beforehand, she could climb stairs or walk up slopes with ease; afterwards, a staircase or a ramp was a threat – a “horrible challenge to be avoided”. She hated this limitation.

Ann, a friend since medical school days, developed pancreatic cancer in her early sixties which, despite surgery, spread to her bones where it caused severe pain. High doses of opiates helped, but getting relief was always a struggle and the next wave of pain was never far from her thoughts.

Mike, a friend of some fifty years, developed a condition in which the membranous ‘bag’ around his heart – the pericardial sac – thickened and, as it tightened, limited his heart’s capacity to pump blood around the body. In fact, he developed heart failure. The condition caused breathlessness; it also caused litres of fluid – oedema – to collect in his legs. The swelling, which gave the skin a reddish hue, made bending his knees and ankles difficult; walking was limited and skipping, one of his former favourite exercises, became impossible. The condition was also uncomfortable with his feet feeling as though they were ‘wrapped in blankets’. Finally, the skin leaked when scratched with a trickle of fluid oozing from the wound for days and risking infection.

How did Mother Nature get it so wrong? Susan’s and Mike’s symptoms were caused by their body’s uncontrolled drive to conserve salt (sodium chloride) and, with it, water. After Susan’s heart attack, and during Mike’s heart failure, their bodies slipped into primitive survival mode. Believing that there must have been an acute loss of blood – as would once have followed a bite by a tiger perhaps! – their reflexes organised for the kidneys to retain salt and water thereby filling the circulation up with a blood alternative. The trouble was that, once started, the retention continued relentlessly, the circulation grossly overfilled and the fluid leaked out into the lungs and the skin causing respectively breathlessness and ankle swelling. If little or no extra salt and water had been conserved, these symptoms would have been avoided.

It would be logical to believe that ankle swelling and shortness of breath offer some advantage; perhaps signalling to Susan and Mike that something was wrong. In fact, as a chronic event it offers nothing but discomfort. That is why the treatment prescribed for both conditions includes diuretics – ‘water-losing’ medicines – and usually they help, at least initially.

Ann’s position was different. The evolutionary advantage of pain is that it warns the sufferer of trouble and allows him or her either to take evasive action or to rest the affected part and so aid recovery. The chronic pain of cancer is caused when the tumour stimulates pain nerve endings in the affected bone or irritates the pain nerves as they pass by. In these circumstances, the sensed pain causes nothing but the perception of persistent hurt. It offers no benefit whatsoever.

If evolution could have gone one step further and arranged for us to turn off these various primitive or aberrant responses, we could manage illness so much better. In causing Susan, Ann and Mike, and countless others, such suffering, Mother Nature has simply created unnecessary trouble. Clearly, she has serious unfinished business to do.

The illustration was created for this blog by Sarah Campbell.