Our sense organs 45

each case. We can only stand amazed at how the
Creator solved this problem, which is why it is
worth giving a little more detail:
Carrying out these specific functions requires an
extraordinarily ingenious molecular construction.
It is the hemoglobin molecule (Hb), which chemically
is a tetrameric iron protein. It consists of a
globin molecule and four heme molecules. Globin
consists of four subunits, namely four long
protein chains (two lots of identical type, i.e. two
pairs). A heme molecule is attached to each of
these chains such that the four heme units lie in
“pouches” close to the surface of the entire Hb
molecule. Heme is a ringshaped molecule, which
contains an iron atom at its centre. Hb consists
of 0.334% iron; the total quantity of iron in the
blood is about 3 grams, or 70% of the iron in the
entire human body.
Protein molecules consist of long chains of various
amino acids, and undergo folding after they
have been assembled. The characteristic threedimensional
structure each protein adopts, which
gives it its function, depends on the types and
sequence of these amino acids. If just a few
(depending on the position, even one) of these
amino acids are substituted by others, or amino
acids are added or omitted, the entire geometry
of the molecule is affected, and thus also its
capacity for gas transport.
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a) In the adult stage (here regarded as commencing
at birth), our blood contains exactly that
hemoglobin (HbA = adult) in which the four protein
chains are constructed so as to give the
entire molecule the precise affinity for oxygen
needed for us to live. HbA has two each of the
already mentioned α und β protein chains. The
chemical structure of these chains must be very
precise, or else severe diseases (anemias) will
result. For instance, sickle cell anemia has arisen
through mutation causing just one single amino
acid residue in the β chain to be replaced by
another. Even this minuscule change results in
an aberrant, pathological form of Hb. We can see
here that the sort of tinkering and experimentation
with amino acid sequences that evolutionary
thinking requires is largely ruled out. The hemoglobin
molecule must be fully functional right
from the start.
b) In the embryonic stage (up to 3 months gestation)
the oxygen transport needs are radically
different. What has the Creator done to cater for
this situation? He has specified the amino acid
sequences in two of the protein chains in the
hemoglobin molecules such that the spatial configuration
after folding results in exactly the oxygen
affinity required. Compared to HbA, instead
of the two β chains there are two ε chains.
Embryonic hemoglobin is thus also called Hbα 2 ε 2
c) In the fetal stage (from 3 months gestation to
birth), the oxygen requirements are different
again. Now the two ε chains of the embryonic
hemoglobin (Hbα 2 ε 2 ) are replaced by two γ
chains. It is now called Hbα 2 ε 2 or HbF (= fetal).
Throughout its development, the fetus must
remain richly supplied with oxygen. Exchanges
of respiratory gases and energy-laden substances
take place in the placenta. If the fetus had the
normal adult hemoglobin HbA, the blood would
be only 60% saturated. Thus the Creator has for
this stage provided the HbF, which is precisely
tuned to the coupling of the fetal and maternal
circulation. Because of its special 3-D structure,
HbF can take up 20-30% more oxygen from the
mother’s blood than HbA. The later replacement
of HbF by HbA occurs through a remarkable
process. Already prior to birth, a “switch of programming”
takes place such that at birth the erythrocytes
only contain some 60-80% of fetal
hemoglobin. At three months of age, the HbF
hemoglobin has been almost completely replaced
by the HbA hemoglobin. It is amazing how all
these processes take place in a completely goaldirected
fashion, in response to the changing circumstances
and needs.
If one were to try to explain the origin of hemoglobin,
and the complex machinery for its synthesis,
from an evolutionary standpoint, there
would be some massively insoluble problems:
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How is it, that in all the three stages of
human development described above, the
exact chemical makeup (the sequences and