Human Accelerated Regions (HAR's) are a set of 49 segments of the human
genome that have been shown to be responsible for some of the most important
areas of divergence between humans and chimpanzees. They are known to
be involved in the development of human neuroanatomy, language, and
complex thought. They are also largely responsible for providing us humans with
opposable thumbs and ankle and wrist joints that enabled us to walk upright
and enjoy pornography.
What is most intriguing about these genes is the rate at which they evolved,
taking a mere 6 million years. How did they evolve so quickly and with such
Traditional understanding of Darwinism is that of natural selection. A principle
which, in itself, is undeniable. But is positive selection enough though to drive
evolution to such complexity? (creationists please read on before posting).
Getting back to what we understand natural selection to be then. For most
of us it represents changes in our 3 billion count code that lead to advantages
with respect to our environment which, in turn, lead to the ongoing breeding of those
traits. But at what level does this occur?
SNP's (single nucleotide polymorphism's) in other words, single, mutational
alterations to DNA that become physically evident (phenotypes) are actually<i>not</i>
related to the mechanisms for the rapid evolution of a particular region of the human
genome, in this case, the HAR's or human traits.
DNA is composed of two 'hand-shake' pairs, one called T-A and the other G-C. As mutation
occurs within a genome, one 'hand-shake' may be substituted for another.
However, one hand-shake is like asking a farmer to date his daughter
(G-C) and the other (T-A) is like meeting your favourite boy-band (if you have a
Please excuse the layman's version if you already know this, I don't mean to patronise
anyone (that means talking down to you).
It has been shown that the rate at which soft 'hand-shakes' are transformed into hard
'hand-shakes' is related to the rate at which mutation occurs and hence, evolution occurs.
The evolution is brought about by changing 'junk DNA' into functional DNA.
The disparities in weak-->strong and strong-->weak are called 'bias in divergence sequences'
or BDS (Bad hanD-Shake). The weak-->strong imbalance is called gBGC (G-C based gene conversion).
BDS occurs in both vertebrates and invertabrates, coding and non-coding regions alike but
is biased towards species and sex (favouring mammals and males).
"The presence of BDS in many HARs prompted the suggestion that gBGC, rather than positive selection, may have
generated the acceleration (Galtier and Duret 2007). Thus we
might expect that HARs showing strong evidence of gBGC
would be less likely to have obtained new functions in human. HAR1 and HAR2 (HACNS1), the two fastest evolving
HARs, have strikingly biased substitution patterns. However,
there is strong experimental evidence of function maintenance
in HAR1 (Pollard et al. 2006) and gain in HAR2 (Prabhakar
et al. 2008)—a surprising result if the human-speciﬁc changes
in these sequences were created by a purely neutral mutational
process. Therefore, we hypothesize that in some evolutionary
scenarios gBGC substitutions may themselves lead to novel
functions, or may set the stage for later adaptive changes,
perhaps due to compensatory substitutions driven by selection."
Ah, so we now have an hypothesis from which to work from.
The hypothesis is that the distribution of base-pairs in a non-functional (junk) region of DNA may in
itself be a force involved in evolution, separate or intrinsic to positive selection.
What other forces than choice could be involved? What indeed are the forces shaping our choices?
I found another article that examines evolution within the context of entropy
"saltations<i>[state changes]</i>, in complexity parlance — appear to be non-linear emergent phenomena, the
result of networked interactions that produce self-organization at ever higher levels. From this perspective,
Darwinian evolution is a mechanism of a higher universal law, perhaps even a variant on the second law of
"a mechanism that coordinates the coevolution of species in an ecosystem to effectively capture, process and
dissipate solar energy into the earth’s shadow … an emergent process founded on the same thermodynamic
imperatives that are thought to underlie all self-organization."
Guy Hoelzer - "On the logical relationship between natural selection and self-organization,"
So how should we really be viewing evolution? It seems positive selection itself seems to imply
some kind of intrinsic understanding of right or wrong. Are we really any differant to creationists for
not questioning this kind of idealism?