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The Body Electric
tively, and they were also eras when great cultural advances were made—
the widespread domestication of fire by Homo erectus in the early Mindel,
and the appearance of Homo sapiens sapiens (Cro-Magnon peoples) and
gradual decline of Neanderthals (Homo sapiens) during the Wurm. Two
other glaciations in the same time span—the Ganz of about 1,200,000 to
1,050,000 years ago and the Riss of about 150,000 to 100,000 years
ago—didn't call forth such obvious advancements in human evolution.
They also differed from the other two in that the average geomagnetic
field intensity was much lower.
Ivanhoe has proposed a direct link from the magnetic field through
the growth-hormone regulator pathways in the brain to account for the
sharp evolutionary gains. He suggests that part of the hippocampus, a
section of the brain's temporal lobe, acts as a transducer of electromag-
netic energy. A part of the hippocampus called Ammon's horn, an arch
with one-way nerve traffic directed by a strong current flow, may read
out variations in the field strength, feeding them by a bundle of well-
documented pathways called the fornix to the hypothalamus and thence
to the anterior pituitary, where growth hormone is produced. It's known
that larger amounts of this hormone in pregnancy increase the size of the
cerebral cortex and the number of its nerve cells in the offspring, as
compared with other parts of the brain. Ivanhoe also notes that the hip-
pocampus and its connections with the hypothalamus are among the
parts of the brain that are much larger in humans than other primates.
The idea gains further support from the fact that neural activity in the
hippocampus increases with electrical stimulation and reaches a max-
imum at 10 to 15 cycles per second, at or slightly above the dominant
micropulsation frequency of today's field. The most powerful shaper of
our development may turn out to be the subtlest, a force that's com-
pletely invisible to us.
Hearing Without Ears
We've considered how the electromagnetic fields of earth, moon, and
sun affect life. In the next chapter, we'll ponder the effects of artificial
fields from our machines. There's probably another interaction, however,
of which we know much less: the effects produced on living things by
the biomagnetic fields of other creatures. If one nervous system could
sense the field of another, it would go a long way toward explaining
extrasensory perception.
Following the curious dogma that what we don't understand can't