Chimpanzee Genome
565
discussed above (Sect. 2.2). Each of these
events generally affects a large number
of DNA sequence positions; however, they
presumably comprise considerably rare oc-
currences during human and chimpanzee
evolution. Insertions and deletions extend-
ing only over a few nucleotides apparently
occur far more frequently in DNA se-
quence evolution. A comparison of around
only 700 kbp of genomic DNA sequence
between humans and chimpanzees has
detected already over 1000 individual in-
sertions and deletions. About half of these
extend over only 1 to 2 nucleotides and
95% do not exceed 20 bp in length.
Currently, it is estimated that a total
of about 4% of DNA sequence in the
chimpanzee and human genomes has no
counterpart in the respective other species.
This indicates that insertions and deletions
contribute substantially both in the num-
ber of events and in the number of affected
positions to the DNA sequence differences
between species. Since insertions and dele-
tions also appear to be commonly located
in functional regions of the genome, they
need to be considered as likely causes for
phenotypic differences between humans
and chimpanzees.
3
Chimpanzees in Evolutionary Research
Prior to describing the relevance of chim-
panzees in evolutionary analyses – I will
only focus on biological evolution and
omit the complex topic of the evolution
of culture – the term
evolution
itself shall
be briefly discussed. In the broadest sense,
evolution can be regarded as mere change
of distinct characters over time. In the
more speciFc view of biologists, evolution
represents heritable changes in a popula-
tion that spread over many generations.
The only changes that can be stably inher-
ited comprise modiFcations in the DNA
sequence. Thus, in a strict sense, biologi-
cal evolution is, ultimately, synonymous
to DNA sequence evolution and evolu-
tionary research aims at identifying the
factors that determine emergence and ac-
cumulation of DNA sequence changes. In
reality, however, it is far more practicable
to study biological evolution at two lev-
els: molecular evolution comprised of the
change of DNA sequences over time, and
the evolution of phenotypes leading to the
differentiation of individual species. This
distinction appears to be indispensable for
the following reasons. The genetic basis
of the vast majority of observed pheno-
typic differences between two species is
generally, and in the better case, not well
understood. Therefore, it is not feasible
to study their evolution on the DNA se-
quence level. ±urthermore, the majority
of DNA sequence changes, at least in the
genomes of mammals, has no effect on
the phenotype since approximately 97% of
the genome has no obvious function. As
a consequence, the evolution of DNA se-
quences is in major parts independent of
the evolution of phenotypes.
However, in order to arrive at a com-
prehensive understanding of biological
evolution, the interdependence of DNA
sequence evolution and phenotypic evolu-
tion needs to be determined. Here, the
analysis of chimpanzees in comparison to
humans is likely to provide relevant new
insights.
3.1
DNA Sequence Evolution
The advantage of DNA sequence compar-
isons between chimpanzees and humans
to shed light on the factors that deter-
mine DNA sequence evolution is twofold.
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