But would we really want to live forever?

Originally published 7 November 1988

Why do we die? I’m not talk­ing about death by acci­dent, mur­der, war, or dis­ease, but the inevitable senes­cence that comes to us all, the cat­a­stroph­ic decline into old age and death that no amount of care, wealth, or con­nivance can delay. A lucky mayfly might sur­vive for as long as four weeks, a tur­tle can live for 150 years, and a human being for a cen­tu­ry — but when your num­ber comes, the time is up.

Why aren’t we immortal?

The ques­tion is not alto­geth­er friv­o­lous. There is at least one good rea­son to won­der why we live for so short a time. Evo­lu­tion should favor long life spans. The longer an ani­mal lives the more off­spring it is like­ly to pro­duce (assum­ing no decline in repro­duc­tive capac­i­ty), and there­fore the greater the chance that its genes will spread through­out a pop­u­la­tion. In Dar­win­ian terms, the repro­duc­tive­ly-active immor­tal organ­ism should be the fittest of all.

But it’s not that sim­ple. The aging and death of indi­vid­u­als may con­fer sub­tle adap­tive advan­tages to a species. Also, an ani­mal is unlike­ly to pro­duce off­spring at an advanced age sim­ply because few ani­mals live that long. With­in most ani­mal pop­u­la­tions, preda­tors dras­ti­cal­ly reduce the num­ber of sur­vivors before senes­cence takes its toll. Among cer­tain wild birds, for exam­ple, only a tiny frac­tion of the pop­u­la­tion sur­vives until old age. A gene which caus­es senes­cence in birds will not be strong­ly select­ed against because the num­ber of birds that reach old age is negligible.

The sit­u­a­tion is rather dif­fer­ent for human beings. With­in the devel­oped coun­tries, espe­cial­ly, human beings are increas­ing like­ly to die of old age rather than by vio­lence or pre­ma­ture dis­ease. In the lin­go of the biol­o­gist, the sur­vival curve for humans is becom­ing ever more “rec­tan­gu­lar” — the per­cent­age of sur­vivors remains fair­ly con­stant with age until about age 70 and them plum­mets precipitously.

Why die?

But what caus­es the rapid decline at three score and ten? Is the aging process trig­gered by genes? Or do cells in the body sim­ply wear out by accu­mu­lat­ing an unsup­port­able num­ber of defects or waste prod­ucts? At a Inter­na­tion­al Genet­ics Con­gress in Toron­to, Olivia Pereira-Smith of Bay­lor Col­lege of Med­i­cine in Hous­ton report­ed data sug­gest­ing that genes do indeed cause aging and death. The work is described in the Oct. 7th [1988] issue of the jour­nal Sci­ence.

Pereira-Smith and her col­leagues stud­ied lab­o­ra­to­ry cul­tures of human cells (colonies of cells grown in a nutri­ent medi­um). Nor­mal cell cul­tures become senes­cent and die after a cer­tain fixed num­ber of dou­blings. But gene muta­tions can lead to excep­tions. Cer­tain immor­tal­ized cell lines — can­cer­ous cells, for exam­ple — will con­tin­ue to divide forever.

By per­form­ing hybridiza­tion exper­i­ments on 26 immor­tal­ized cell lines, the Bay­lor group amassed evi­dence to sug­gest that as few as four genes might be respon­si­ble for senes­cence in nor­mal cells. The group is now try­ing to iden­ti­fy the genes.

It’s a long way from study­ing cell cul­tures in lab­o­ra­to­ry flasks to under­stand­ing entire organ­isms. Nev­er­the­less, the report of the Bay­lor researchers inspires a bit of wide-eyed spec­u­la­tion. Biol­o­gists have acquired the abil­i­ty to mod­i­fy genes. Might it be pos­si­ble some­day to engi­neer a strain of humans who are not pro­grammed for aging and death? Is immor­tal­i­ty an option, not for us but for that future race of Homo aeter­nus?

Tinkering with the clock

Senes­cence in humans is a com­pli­cat­ed mix of sub­tle and obvi­ous changes, none of which sci­en­tists yet ful­ly under­stand. But if aging and death are pro­grammed by genes, then I would­n’t bet against the pos­si­bil­i­ty that extrav­a­gant­ly long life­times can be engi­neered. Geneti­cists will cer­tain­ly learn to tin­ker with the bio­log­i­cal clock that ticks inex­orably in every cell, and maybe — just maybe — post­pone the alarm that announces decay and death.

The per­son­al and social impli­ca­tions of immor­tal­i­ty are stag­ger­ing. If over­pop­u­la­tion is already a prob­lem, what will hap­pen in a world where indi­vid­ual human beings can live for­ev­er — assum­ing, of course, that they stay out of the way of germs, bul­lets, speed­ing auto­mo­biles, and oth­er exter­nal threats to life?

And would we want to live for­ev­er if we had the choice? Do we real­ly envy Methuse­lah? Can you imag­ine a love affair last­ing 900 years? Or 900 years of pres­i­den­tial debates? The Hyper­bore­ans of Greek myth lived for a thou­sand years, free of ills, in a land of eter­nal sun­shine beyond the north wind; they leaped into the sea like lem­mings to escape boredom.

It is scary to con­tem­plate what immor­tal­i­ty might mean for the human species. I asked a friend if he would want to dis­cov­er the Foun­tain of Youth; no, he said, but he would­n’t mind dis­cov­er­ing the Foun­tain of Mid­dle Age. For myself, I sus­pect that longer life­times would bring more grief than bliss. Nat­ur­al selec­tion had mil­lions of years to per­fect the cel­lu­lar appa­ra­tus of life, pre­sum­ably to the advan­tage of our species. I doubt if the Ponce de Leons of genet­ic sci­ence will improve upon Moth­er Nature’s plan.