"Recent science news suggests that our days are numbered. Our hearts begin to beat sooner than scientists had thought, Medical Xpress says, but quickly notes that humans get a normal limit of about 3 billion heartbeats – some more, some less. To find out about the onset of heartbeats, the British Heart Association studied mouse embryos. Extrapolating their measurements to human gestation, they think the human heart begins beating just 16 days after conception. “Previously, it was thought that the heart started to contract a stage later, when the heart appears as a linear tube,” the article says, so this is a dramatic finding. The heart is the first organ to form during pregnancy. It will beat for many years—but not forever.But “When, and why, must we die?” PhysOrg wonders. The author of this article gives a common evolutionary explanation:
We must die eventually, he suggests,
because humans have a body design that evolved to
hang in there long enough for us to live long enough to reproduce, ensuring the survival of the species. Once we’ve accomplished that, he suggests,
nature has been spectacularly indifferent to parts that wear out,
electrical currents that short-circuit, and cells
that act on bad information and replicate like crazy.
Our bodies, in short, did not evolve to live into extreme old age.
Instead, there appears to be a built-in limit to human lifespan.
What could be the biological causes of this limit to human lifespan? The idea that ageing is a purposeful, programmed series of events that evolved under the direct force of natural selection to cause death has now been all but discredited.
Instead, what appears to be a ‘natural limit’ is an inadvertent byproduct of fixed genetic programs for early life events, such as development, growth and reproduction. Limits to the duration of life could well be determined by a set of species-specific, longevity-assurance systems encoded in the genome that counteract these inadvertent byproducts, which are likely to include inherent imperfections in transferring genetic information into cellular function. To further extend human lifespan beyond the limits set by these longevity-assurance systems would require interventions beyond improving health span, some of which are currently under investigation. Although there is no scientific reason why such efforts could not be successful, the possibility is essentially constrained by the myriad of genetic variants that collectively determine species-specific lifespan."
CEH
The days of our years are threescore years and ten; and if by reason of strength they be fourscore years, yet is their strength labour and sorrow; for it is soon cut off, and we fly away. Psalm 90:10
