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Human/chimp
DNA similarity by Dr Donald James Batten
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Dr
Donald James Batten: Creationist Agricultural Scientist
(Honors/Awards/Associations) 1976–90: Research
Horticulturist, NSW Agriculture, Tropical Fruit Research
Station, Alstonville. 1991–1994: Senior Research Horticulturist,
NSW Agriculture, Tropical Fruit Research Station, Alstonville
(resigned January 1994). 1994– : Creation Science Foundation,
Brisbane, Australia + private horticultural consultant.
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The
idea that human beings and chimps have close to 100% similarity
in their DNA seems to be common knowledge. The figures quoted
vary: 97%, 98%, or even 99%, depending on just who is telling
the story. What is the basis for these claims and do the data
mean there really is not much difference between chimps and
people? Are we just highly evolved apes?
The following concepts will assist with a proper understanding
of this issue: Similarity (‘homology’) is not evidence for common
ancestry (evolution) as against a common designer (creation).
Think about a Porsche and Volkswagen ‘Beetle’ car. They both
have air–cooled, flat, horizontally–opposed, 4–cylinder engines
in the rear, independent suspension, two doors, boot (trunk)
in the front, and many other similarities (‘homologies’).
Why do these two very different cars have so many similarities?
Because they had the same designer! Whether similarity is morphological
(appearance), or biochemical, is of no consequence to the lack
of logic in this argument for evolution. If humans were entirely
different from all other living things, or indeed if every living
thing was entirely different, would this reveal the Creator
to us? No! We would logically think that there must be many
creators rather than one.
The unity of the creation is testimony to the One True God who
made it all (Romans 1:18–23). If humans were entirely different
from all other living things, how would we then live? If we
are to eat food to provide nutrients and energy to live, what
would we eat if every other organism on earth were fundamentally
different biochemically? How could we digest them and how could
we use the amino acids, sugars, etc., if they were different
from the ones we have in our bodies?
Biochemical similarity is necessary for us to have food! We
know that DNA in cells contains much of the information necessary
for the development of an organism. In other words, if two organisms
look similar, we would expect there to be some similarity also
in their DNA. The DNA of a cow and a whale, two mammals, should
be more alike than the DNA of a cow and a bacterium. If it were
not so, then the whole idea of DNA being the information carrier
in living things would have to be questioned. Likewise, humans
and apes have a lot of morphological similarities, so we would
expect there would be similarities in their DNA. Of all the
animals, chimps are most like humans,1 so we would expect that
their DNA would be most like human DNA.
Certain biochemical capacities are common to all living things,
so there is even a degree of similarity between the DNA of yeast,
for example, and that of humans. Because human cells can do
many of the things that yeast can do, we share similarities
in the DNA sequences that code for the enzymes that do the same
jobs in both types of cells. Some of the sequences, for example,
those that code for the MHC (Major Histocompatibility Complex)
proteins, are almost identical. What of the 97% (or 98% or 99%!)
similarity claimed between humans and chimps?
The figures published do not mean quite what is claimed in the
popular publications (and even some respectable science journals).
DNA contains its information in the sequence of four chemical
compounds known as nucleotides, abbreviated C,G,A,T. Groups
of three of these at a time are ‘read’ by complex translation
machinery in the cell to determine the sequence of 20 different
types of amino acids to be incorporated into proteins. The human
DNA has at least 3,000,000,000 nucleotides in sequence.
Chimp DNA has not been anywhere near fully sequenced so that
a proper comparison can be made (using a lot of computer time
to do it—imagine comparing two sets of 1000 large books, sentence
by sentence, for similarities and differences!). Where did the
‘97% similarity’ come from then? It was inferred from a fairly
crude technique called DNA hybridization where small parts of
human DNA are split into single strands and allowed to re–form
double strands (duplex) with chimp DNA.2
However, there are various reasons why DNA does or does not
hybridize, only one of which is degree of similarity (homology).3
Consequently, this somewhat arbitrary figure is not used by
those working in molecular homology (other parameters, derived
from the shape of the ‘melting’ curve, are used). Why has the
97% figure been popularised then? One can only guess that it
served the purpose of evolutionary indoctrination of the scientifically
illiterate.
Interestingly, the original papers did not contain the basic
data and the reader had to accept the interpretation of the
data ‘on faith’. Sarich et al.4 obtained the original data and
used them in their discussion of which parameters should be
used in homology studies.5 Sarich discovered considerable sloppiness
in Sibley and Ahlquist’s generation of their data as well as
their statistical analysis.
Upon inspecting the data, I discovered that, even if everything
else was above criticism, the 97% figure came from making a
very basic statistical error—averaging two figures without taking
into account differences in the number of observations contributing
to each figure. When a proper mean is calculated it is 96.2%,
not 97%. However, there is no true replication in the data,
so no confidence can be attached to the figures published by
Sibley and Ahlquist. What if human and chimp DNA was even 96%
homologous?
What would that mean? Would it mean that humans could have ‘evolved’
from a common ancestor with chimps? Not at all! The amount of
information in the 3 billion base pairs in the DNA in every
human cell has been estimated to be equivalent to that in 1,000
books of encyclopaedia size.6 If humans were ‘only’ 4% different
this still amounts to 120 million base pairs, equivalent to
approximately 12 million words, or 40 large books of information.
This is surely an impossible barrier for mutations (random changes)
to cross.7 Does a high degree of similarity mean that two DNA
sequences have the same meaning or function? No, not necessarily.
Compare the following sentences: There are many scientists today
who question the evolutionary paradigm and its atheistic philosophical
implications. There are not many scientists today who question
the evolutionary paradigm and its atheistic philosophical implications.
These sentences have 97% homology and yet have almost opposite
meanings! There is a strong analogy here to the way in which
large DNA sequences can be turned on or off by relatively small
control sequences. The DNA similarity data don’t quite mean
what the evolutionary popularisers claim! |
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