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on Unit 4 in Towle’s Modern Biology*: Origin-of-Life
and Evolution
Chapter
14: Origin-of-Life
The
unit talks about the origin-of-life and biological evolution.
The former is defined to be atoms to the first cell,
while evolution is the first cell to humans. Chapter
14 puts a positive spin on the very disappointing results
of origin-of-life experiments. In 1953 Stanley
Miller successfully produced some amino acids in an
experiment believed to simulate prebiotic conditions.
Since then fifty years of experimentation have not added
to that initial success in any meaningful way. All attempts
to show how proteins, RNA and DNA arose in prebiotic
conditions have failed.
The
section on page 268 entitled “From Molecules to
Cell-like Structures” is an attempt to convince
students that cells are not that much more complex than
inanimate materials and, therefore, it is reasonable
for them to believe that they arose from nonliving matter.
To demonstrate this consider the section’s use
of the terms “protein molecules”, “enzymes”
and “cell-like structures”.
First
the use of “protein molecules”. The fact
is that scientists have tried unsuccessfully for decades
to determine how proteins came into existence. But the
section claims that “protein molecules”
“form spontaneously in the laboratory from solutions
of simple organic chemicals”. That falsehood along
with the one on the preceding page that claims scientists
have made nucleotides are inexcusable. Proteins and
nucleotides, the building blocks of RNA and DNA, are
the most important molecules in cells. How could these
errors escape the attention of the many contributors
and reviewers listed in the front of the book?
Secondly
the role of enzymes in catalyzing chemical reactions
is misrepresented. The fact is that any chemical reaction
that occurs with enzymes will also occur without them
but they will occur more slowly. Likewise enzymes in
cells do not cause or prohibit reactions but rather
greatly increase the speed of reactions. Therefore,
the claim that experiments have shown that “some
important aspects of cellular life” can arise
without enzymes is wrong in two ways. First experiments
are not needed to demonstrate what is commonly known
about enzymes. Secondly their claim that some enzymes
in cells may not be needed is bogus because it misses
the point that what enzymes do is speed up reactions.
This misrepresentation begs the same question as the
one appearing at the end of the previous paragraph.
It would seem the purpose of this charade is to suggest
that cells are not that special. Consider this sentence,
“Thus, these studies suggest that the gap between
the nonliving chemical compounds and cellular life may
not be quite as wide as previously thought.”
Thirdly,
the ambiguous term “cell-like structures”
is used repeatedly and the implication is that the only
thing they lack from being alive is hereditary material.
In fact, the suggestion is made on page 270 that “The
self replicating RNA would have provided the hereditary
information that the cell-like structures lack.”
The “cell-like structures” have some of
the properties of cells but so do soap bubbles, balls
of mercury and just about everything else. The bottom
line is that in 50 years of origin-of-life experiments,
scientists have not made anything remotely similar to
a cell including proteins, nucleotides, RNA and DNA.
They do not know how any cellular structure or cellular
process came into existence. Students have the right
to know that in unambiguous terms.
As
to the experiments to make an RNA replicator (p. 270),
students should be told the following. Decades-worth
of experiments to make RNA under prebiotic conditions
have not been successful. This includes all types of
RNAs, not just ribozymes. Experimenters point out the
many problems at the various stages of synthesizing
RNA. RNA is made of nucleotides and each nucleotide
consists of three parts: a five carbon sugar called
a ribose, a nitrogen base and a phosphate. If all the
ingredients of nucleotides are mixed together, nucleotides
do not result. The conditions that are right to produce
a particular part, such as ribose, are devastating to
the production of the nitrogen bases. The temperature,
Ph and water content must be adjusted for each part
to synthesize. To get around this problem, experimenters
make the parts separately and then bring them together,
which would seem to violate the spirit of a prebiotic
reaction. But even with a human element injected into
the experiment, problems still abound. In the presence
of water, nucleotides tend to dissemble rather than
assemble. Not only will the nucleotides of cellular
RNA form, but also many analogs that will interfere
with the assembly of the RNA. The analogs result from
the bonding of the base and the phosphate to different
positions on the ribose. Also many sugars other than
ribose would form and since they are chemically similar
to ribose would form more nucleotide analogs. The presence
of numerous analogs would greatly diminish the probability
that a chain of nucleotides would form that was absent
of analogs. And if the improbable does occur and a pure
chain does result, the improbability is compounded by
the likelihood that the RNA will not be a ribozyme.
These and other problems have led one experienced experimenter
in the origin-of-life field to refer to RNA as “the
pre-biotic chemist’s nightmare”.
Suppose
scientists succeed in showing how proteins, DNA and
RNA evolved. How large is the next step to a cell? Here
are two opinions by prominent scientists.
The
biochemist David Green writes in his book Molecular
Insights into the Living Process: “the macromolecule-to-cell
transition is a jump of fantastic dimensions, which
lies beyond the range of testable hypothesis. In this
area all is conjecture. The available facts do not provide
a basis for postulating that cells arose on this planet.”
Francis
Crick, one of the discoverers of DNA, writes in his
book Life Itself: “An honest man, armed
with all the knowledge available to us now, could only
state that in some sense, the origin of life appears
at the moment to be almost a miracle.”
Chapters 15-18: Evolution
This
material skirts the issue of how macro-changes occurred
in organisms, such as the feathered wing, vertebrae,
legs, amniotic reproduction system, invertebrates to
vertebrates, single cell to multicell organisms, classes
of vertebrates, namely, fish, birds, reptiles, mammals
and amphibians, etc. It does not talk about a mechanism
for macro-change or provide evidence that it has occurred.
Still the tenor of the whole unit will leave little
doubt in a student’s mind that evolution was the
cause.
On
the other hand, the unit devotes many pages to micro-changes,
those changes that occur at the species-level that no
one disputes. I refer to the material on Darwin in Chap.
15, and all of Chap. 16. Even Chap. 17 on human evolution
talks about the differences between species of the same
genus, small potatoes in comparison to the changes at
the levels of phyla, classes, orders and families.
Cherry-picking in the fossil record
First
Table 14-1 lists four isotopes used in radioactive dating,
carbon and three more. The text explains that since
carbon is found in living organisms, it can be used
to date fossils. However, because of the relatively
short half-life of carbon, it can only be used to date
fossils that are less than 60,000 years old. It then
explains that the other three isotopes are used to date
older fossils because they have longer half-lives. Here
is the cherry-picking part. Many, if not most, students
will infer that these isotopes are, like carbon, found
in fossils. Why aren’t students told that these
isotopes are not found in fossils? Why aren’t
they told that these isotopes are not even found in
the sedimentary rocks that contain the fossils? Could
it be to keep students from knowing that the radioactive
dating of fossils is very indirect and, therefore, subject
to error?
Another
picking of cherries-- the distribution of fossils in
the earth as explained on pages 280-281. Table 15-1
Geological History of Earth is very effective at giving
the impression that it represents stacked horizontal
layers of rock with humans and other “modern”
vertebrates in the upper layers and “primitive”
vertebrates and marine invertebrates in lower layers.
Many students will be so impressed and, thereby, infer
that this sequence of layers actually exists and, furthermore,
exists in most places. The fact is that it is not found
ANYWHERE on earth. Also it is not unusual for fossils
that are thought to be millions of years older to be
above younger fossils. There are many more things that
are lacking but at the very least this minimum amount
of information should be provided to students.
Finally
the most egregious example of cherry-picking in the
fossil record- -the absence of a discussion of transitional
fossils. Transitional fossils constitute the most important
aspect of the fossil record for determining if all organisms
are connected by an evolutionary process. There would
be no better evidence than numerous sequences of fossils
showing slight changes accumulating to make big changes--
a sequence that starts with a fish and ends with a frog,
a sequence that shows the gradual evolution of a feathered
wing from a reptile scale. On the other hand the absence
of transitional fossils is very damaging to evolution
to the point of falsifying it. By comparison other aspects
of the fossil record, such as the vertical distribution
of fossils in the strata, and their geographical distribution
have less evidentiary value. So why does the textbook
discuss the latter but not the former?
Evolutionary
Trees
These
are found on pages 287, 343, 581, 672, 745, 800, 821,
841, 862, and 891. They imply that every point on them
represents a species that existed in the past and we
have their fossilized remains. Not so! Only the tips
of the branches represent known species. They should
be removed from the textbook.
*A.
Towle, Modern Biology, (Austin, Texas: Holt,
Rinehart and Winston, 1999)
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