[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: pineal gland notes



Still attempting to probe Flying Goat's thoughts...

>     What I was supposing about the weather after the BIG SMACK was that it
>probably was turbulent and violent immediatly following (like on Jupiter, you
>know...) and then settling in for a really long dismal warm fog.  

Or cold fog...

>If, instead of
>seasons to tell you to when to breed, you just got unending fog for perhaps
>years,  [...]

>    If this situation existed like this for a while, wouldn't it be an
>advantage for an organism to be able to measure time passing with some other
>function that could still measure lengths of time exposed to light to detect
>whether the days were longer or shorter?  That wouldn't spend the whole time
>of fog thinking it was just a nasty Autumn that spanned years?

This is where you've really lost me; I tried to ask this before, but
perhaps I wasn't clear.  In modern organisms, the pineal gland
regulates activity based on the length of days.  It is also
responsible for some of the synchronization between activity patterns
and the day/night cycle.  As such, it seems to me that animals with a
well developed pineal gland (with or without the extra-ocular
photoreceptors) relying on such cues would be *more* rather than less
effected by a sudden long night (or autumn).  Why do you seem to think
the opposite?

>     The only other way I can think of to measure what season it is has to do
>with being able to measure magnetic polarities, and if it's sensitive enough,
>being able to detect the seasonal tilts of the Earth.   

I'm afraid you have a bit of confusion here.  The earth does not
change its tilt.  The earth's tilt remains constant.  Think about a
simple model of the solar system containing only the sun and the earth
with the earth revolving around the sun in a circular orbit.  Add to
that the earth's rotation about its own axis.  Now incline the axis
slightly so that it is say, 23 degrees, away from being perpendicular
to the plane of the orbit.  Now move the Earth around its orbit
making sure that the axis of rotation at any given time is parallel to
its axis of rotation at any other point in its orbit.  That's much
closer to the actual scenario than what you seem to be picturing
above.  Furthermore, even if the earth did wobble as you've proposed,
the magnetic field would wobble right along with it.  

I'm also curious about your statement of the "polarities".  Magnetic
North and South switch places at somewhat random intervals with a mean
time between flipping on the order of 17,000 years (I can double check
that if anyone cares for precision).  Most studies of birds and
magnetism claim that the birds are insensitive to the actual magnetic
field vector, so this doesn't make a difference to them.  They
reportedly only detect the field's inclination (i.e. the angle that
the field makes with the plane parallel to the ground).

>I know birds can tell which way north is but I have no idea whether
>they can tell what time of the year it is using this magnetic
>sympathy they have.  If some birds have this ability, did therapods?

I'm glad you know that about birds :-)  I'm not sure that many other
people are so certain.  There are a lot of reports indicating magnetic
sensitivity in birds, bees, mollusks, porpoises etc. etc.  However,
lacking a strong candidate for a mechanism in all animals except for
elasmobranch fish (i.e. sharks, skates and rays), most or all such
reports leave room for debate as to whether or not the animals really
use the cues that people claim they are using.  In any case, even if
they do, as I outlined above this probably wouldn't help them.  Well,
on the other hand, if they could monitor the perturbations in the
magnetic field caused by the solar wind, I suppose there's a
possibility.  I personally would need a lot of convincing before I'd
believe such a scenario, though.

>    If the pineal glands functions are superceded in mammals by the
> receptors in the eyes, is it possible dinosaurs could do this also?   If we
>mammals use our eyes to do this, why do we still have the damn pineal gland?

I'm afraid that I must not have been clear about this.  The pineal
glands of some vertebrates are directly sensitive to light.  In
others, they are not.  Regardless of whether or not there are cells in
the gland which are directly responsive to light, the pineal glands of
most animals modulate the level of hormones in the body dependent upon
the time of day or the time of year.  So what I was saying is that the
light-sensitivity of the pineal gland has been lost in a lot of
animals.  However, in many cases the pineal's function as an endocrine
gland has remained.  (I'm by no means an expert in this area, but I
have a friend who studies chronobiology.  I'm going to forward the
relevant parts of this message and ask for clarifications and/or
corrections.) 

-- 
Mickey Rowe     (rowe@lepomis.psych.upenn.edu)