{"id":1230,"date":"2024-08-07T23:51:20","date_gmt":"2024-08-07T23:51:20","guid":{"rendered":"https:\/\/joshmitteldorf.peachpuff-wolverine-566518.hostingersite.com\/?p=1230"},"modified":"2024-08-07T23:51:20","modified_gmt":"2024-08-07T23:51:20","slug":"funeral-by-funeral","status":"publish","type":"post","link":"https:\/\/scienceblog.com\/joshmitteldorf\/2024\/08\/07\/funeral-by-funeral\/","title":{"rendered":"Funeral by Funeral"},"content":{"rendered":"

My title is taken from a well-known but less-well-authenticated quote from Max Planck: \u201cScience progresses funeral by funeral.\u201d\u00a0<\/span><\/p>\n

Planck discovered the quantum principle in 1899, before the the physics world was ready for it. Eventually he was hailed as a visionary; but we can imagine his frustration when the smartest physicists in the world were refusing to consider his ideas because they were an unthinkable departure from the way they thought the world worked. Planck waited more than 20 years for his vindication.<\/span><\/p>\n

Last week, we lost Len Hayflick (1928 – 2024), a giant in the field of biology of aging. As a young researcher in the 1960s, Hayflick discovered that cells in culture had a finite lifetime. They would replicate for a few hundred generations, then stop replicating. This contradicted a dogma (attributed to <\/span>Alexis Carrel<\/span><\/a>) that had been prevalent for more than forty years, which said that even though animals and plants have finite lifespans, their cells were, in principle, immortal.\u00a0<\/span><\/p>\n

At the time of Hayflick\u2019s discovery, DNA was relatively new, and the fact that chromosomes had protective DNA tails, called telomeres, was not yet known. Within 15 years, the full story came out: When DNA is copied during cell replication, a piece of each end is left uncopied. Related to this, the DNA includes a buffer of meaningless, repetitive DNA at each end so that no information is lost when the cell replicates. However, eventually the telomere is exhausted and if the cell were to replicate further, information in the coding DNA would indeed be lost.<\/span><\/p>\n

This could, in principle, be an existential threat to all life. But never fear! Nature has provided a solution, in the form of an enzyme called telomerase.<\/span><\/p>\n

The curious thing is that telomerase is turned off by default, allowing the telomere to shorten, with life-threatening consequences. You remember from basic biology that there are two modes of cell replication, called mitosis and meiosis. Mitosis is just the cell splitting in half, each half growing anew Meiosis begins with the merger of two cells, followed by an unnecessarily complex sequence of divisions and recombinations. Another word for meiosis is \u201csex\u201d.\u00a0<\/span><\/p>\n

It is a fact of biology going back to the single-celled eukaryotes (ciliates) that telomerase is switched on only during sex, but not during mitosis. What is this about? A few years ago, I created a <\/span>computer model<\/span><\/a> to demonstrate how this withholding of telomerase might have evolved as a way to prevent cells from the danger of unrestrained reproduction without sharing genes. Yes, evolution had to coerce cells, compelling them to have sex. Coercion seems to be less necessary for bonobos. \"What<\/span><\/p>\n

The evolutionary significance of telomere dynamics<\/strong><\/h1>\n

My point is that telomerase has very low metabolic cost and withholding it has very steep consequences for what is usually called \u201cfitness\u201d. Withholding telomerase, allowing cell senescence to happen after a few hundred generation, is the earliest example of programmed death, and to this day, telomere shortening is a factor in the aging and death of higher animals, including ourselves.<\/p>\n

Thus, telomere attrition is the clearest evidence that aging is not a failure of evolution but an active biological function. Aging has been part of evolution\u2019s plan for life since before there were multi-celled plants and animals.<\/p><\/blockquote>\n

This conclusion is rightfully an important part of Hayflick\u2019s legacy, a clear implication of his signature discovery. Young Hayflick had the temerity to defy the academic establishment and to pronounce what was at the time a radical reversal of scientific dogma. But he never embraced the obvious implication \u2014\u00a0<\/span><\/p>\n