INTELLIGENT DEVELOPMENT 165should not be surprising: ge ne tic variance for impor tant traits will tend
to be much reduced by natu ral se lection or by epige ne tics.
Blood pressure in humans and animals also shows great individual dif-
ferences. Heritability studies have produced widely divergent estimates of
heritability, again based on the unreliable twin method. Already we are see-
ing that trying to draw a parallel between IQ and physiolog y is not so easy.^26
Th ere are mea sures of many other aspects of physiology. Th ese include
heart rate, skin re sis tance, skin temperature, muscle tension, neuro-
electrical activity, and dozens more. However, one of the most striking
things about physiological functions is the extremely wide range of
variation within which normal, adequate function seems to operate.
Th e following list pres ents the normal ranges of markers of physiological
functions in a standard full blood count. Th ese levels are all critical indi-
cators, or biomarkers, of complex physiological functions. Only deviations
beyond these wide limits suggest abnormality:
Red blood cells: 4.5–6.5 trillion cells per liter
White cells: 4.0–11.0 billion cells per liter
Platelets: 140–400 billion per liter
Neutrophils: 2–7.5 billion per liter
Lymphocytes: 1.5–4.0 billion per liter
Monocytes: 0.2–0.8 billion per liter
Vitamin B12: 150–1,000 nanograms per liter
Serum ferritin: 12.0–250 micrograms per liter
Serum folate: 2.0–18.8 micrograms per liter
Vitamin D: 50–75 nanomoles per liter
Serum urea: 2.5–7.8 micromoles per liter
Serum creatinine: 75–140 micromoles per liter
Serum albumin: 35–50 grams per liter
Alkaline phosphatase: 30–130 microns per liter
Serum globulin: 20–35 grams per liter
Immunoglobulin A: 0.5–4.0 grams per liter
Immunoglobulin G: 5.5–16.5 grams per literWhat these fi gures suggest is that, within these very wide limits of
variation, the system functions well enough. In a dynamic, interactiveThis content downloaded from 139.184.14.159 on Tue, 17 Oct 2017 13:53:16 UTC