Can anyone explain what happens to telomere length when a new human is born? Presumably the telomere length is reset? Is there a beneficial reason for telomeres shortening with time?
Telomeres "shorten" when DNA is copied for cell replication; the benefit of this is that it means telomeres quickly whittle down to nothing, and kill the resulting cells, when a rogue cell line has started replicating an unnecessary number of times- e.g., in cancer.
Is it practical to harness this somehow to extend life then?
Of course whether this would actually meaningfully extend life is uncertain- aging is complicated.
I also wonder whether there is a second advantage to telomere depletion; reducing the instances of organisms from different generations carrying the same genes competing for resources. After all, we're here for the benefit of our genes, not the other way round.
Here's a paper comparing max life span (MLS) against body temperature, body mass, and telomere length. [1]
[1] http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3680702/figure/F...
I'd be happy with toenail fungus. Or mild eczema. Or, really, any medical condition whatsoever.
You realize people are still arguing over why your joints make a "pop" sound when you crack them, right ? Like, they've sort of settled on the air bubbles rapidly escaping the joint, but ... there's still a debate.
I think we also need to figure out how to stop noses and ears from growing.
So does this mean that without this shortening of the telomeres, the incidence of cancer would be much larger? That the cancers that actually manifest are a small fraction of the potential cancers aborted by this defense mechanism?
The DNA damage checkpoint is interesting all the way through public health policy in 2 cases: 1) The BRCA gene is a DNA repair protein. Women with a mutated brca gene are missing one of those 3 checkpoints. 2) HPV (for which we have a complete vaccine) is of a type of virus that is generally destroyed by your DNA-repair machinery. However HPV, being evolutionary wily, has a specific mechanism to shut down your own DNA repair machinery that would otherwise catch the foreign invader. Hence, HPV 'causes cancer' by deliberately disabling one of those checkpoints.
http://phys.org/news/2011-09-body.html
Early embyros have a lot in common with negligibly senescent lower species like hydra in that they are in a state of always-on regeneration. Repair everything, all the time. That state of being was lost somewhere along the way to organisms that have complex nervous systems made up of long-lived cells and structures that have to record state. An adult human couldn't operate like a hydra and live.
The setup for most species is that adults have small groups of stem cells with telomerase and unlimited self-renewal, but the bulk of tissue is made up of somatic cells without telomerase, or with much less telomerase activity, that have a limited number of divisions before self-destruction or clearance by the immune system. Stem cells produce in a small number of new somatic cells as needed, and are the only tiny set of cells with the unlimited replication privilege. Telomere length is a part of the countdown mechanism that limits divisions in somatic cells - see the Hayflick Limit - because of the end replication problem in that a little of the length is lost with each cell division. This situation is shaped by the existence of cancer. The whole arrangement looks very much like something that came into being to fend off cancer, with ever more checks and balances arising to prevent uncontrolled replication, while still incorporating the mechanisms needed for embryonic growth and later regeneration.
The telomere is a solution to this problem; you just pad the ends of your chromosomes with useless repetitive sequence so if you do lose a bit while replicating it doesn't matter. Any anti tumor properties of this system are an ancillary benefit.
If that were true though wouldn't successive newborns have shorter and shorter telomeres?
So that people die instead of reproducing when they're old
As I understand it, after we've reproduced and raised children - which we generally do before age-related illnesses kick in - we only have limited evolutionary value and no longer face stringent selection pressures. So it's probably that there were few opportunities for evolution to correct age related illnesses, or few survival-of-the-fittest opportunities (since we've already reproduced by the time they occur). However, this theory ignores the ability for grandparents to look after children. I suppose it's only minor enough for us to have evolved to live to ~80 but doesn't require youthful health any more.