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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. |
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!
For more information
on creation, please go to Answers
in Genesis
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