[LEAPSECS] Does the "leap second" matter?

[Kevin Birth]

I have to admit that the idea of biological clocks makes me cringe a bit.
This is because "clock" is a metaphor that is constraining biological and
neuroscientific research right now.  Partly, this is because these
scientists do not think very critically about clocks (they would benefit
from reading this list!), and their idea of what clocks are is largely a
mechanical clock.

Biological systems are not clocks. If they were good clocks, we'd have no
need for clocks.  Instead, the circadian cycles that Dava talks about and
which Cziesler has done extensive research on are systems that are very
good at maintaining themselves for durations on the order of a few days,
but they need a time  time reference to continue to function properly.  In
most species, the time reference is exposure to light (particularly
sunrise).  Without the time reference, the cycles drift.  A good example
of this is the day/night reversal experienced by some indigenous arctic
populations during the winter months.

Without a time reference, there is also the danger of what is called
internal desynchronization.  There is growing evidence that every cell has
oscillators capable of free-running, but they do not all run exactly
alike.  The coordination of cells in multicellular organisms is handled by
hormonal cycles controlled by neural bodies like the suprachiasmatic
nucleus in mammals that use light to entrain robust @24 neural cycles that
then signal the rest of the body.  Internal desynchronization is
unpleasant in the short run (jet lag is an example) and has serious health
consequences in the long run.

As a result, time in biological systems is different from a continuous
timescale since the biological systems are designed to reset every day
and, depending on latitude, drift with varying seasonally durations of
daylight.  Putting critters (including humans) in conditions isolated from
time cues is interesting, but such research only studies half of the
system.  From an evolutionary perspective, organisms adapt to the variable
cycles of their environments not to abstract uniform time.  The exception
to this is our species, a rather strange animal that can entrain its
circadian cycles to events shaped by clock time such as nighttime
television or early morning broadcasts of cricket tests from multiple time
zones away.  It is a species can even adopt behavioral cycles that cause
cognitive impairment through sleep restriction for the purpose of
improving education.

Cheers,

Kevin





Kevin K. Birth, Professor
Department of Anthropology
Queens College, City University of New York
65-30 Kissena Boulevard
Flushing, NY 11367
telephone: 718/997-5518

"We may live longer but we may be subject to peculiar contagion and
spiritual torpor or illiteracies of the imagination" --Wilson Harris

"Tempus est mundi instabilis motus, rerumque labentium cursus." --Hrabanus
Maurus





On 8/3/13 2:28 PM, "Rob Seaman" <seaman at noao.edu> wrote:


>On Aug 3, 2013, at 10:09 AM, Richard B. Langley <lang at unb.ca> wrote:

>

>> http://www.bbc.co.uk/news/world-23559189

>

>Define "matter" ;-)

>

>The exchange about circadian rhythms has a more recent calibration of

>24.18 +/- 0.04 days:

>

>	http://news.harvard.edu/gazette/1999/07.15/bioclock24.html

>

>We're apparently pretty good biochemical clocks.

>

>Rob

>

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