I’m currently reading – devouring would be a better word – Sean B. Carroll’s book The Making of the Fittest: DNA and the Ultimate Forensic Record of Evolution. It’s a well-written, gripping and persuasive account of how DNA evidence is providing irrefutable confirmation for the key mechanisms of evolution: descent with modification and natural selection.
This is a revolution that has occurred mainly within the past twenty-five years. Carroll explains how, in 1982, our total knowledge of DNA sequences from all living species would have filled a book about the size of his own (i.e. fewer than a million characters). By 2006, this had increased 40,000-fold, so that the books required to hold all the DNA text we now possess could be stacked to more than twice the height of the Sears Tower, with the pile growing by more than 30 storeys per year. This DNA evidence is enabling biologists to see how natural selection has operated at the level of genes to create the vast diversity of life we see around us.
One of the most persuasive and fascinating points made by Carroll relates to the DNA evidence for common descent among humans, apes and monkeys. Large amounts of DNA within our genome is non-coding (or “junk”) DNA: DNA that has no apparent function in creating proteins within the organism. The significance of this non-coding DNA is that natural selection does not operate upon it: it just sits there without alteration, other than the occasional harmless mutation.
Occasionally, a DNA copying error leads to chunks of this non-coding DNA being inserted into the genome near genes. These can either be “long interspersed elements” (LINEs) or “short interspersed elements” (SINEs). As Carroll explains (p.99), “once a SINE or LINE is inserted, there is no active mechanism for removing it”. Equally, the odds of two identical SINEs or LINEs arising by chance are almost non-existent.
Hence SINEs and LINEs provide a perfect indicator of shared descent. If two species contain the same SINE or LINE within their DNA then this can only be explained by their sharing a common ancestor. SINEs therefore provide a means for biologists to trace species’ kinship “beyond any doubt” (p.99).
This then brings us to the image at the top of this post, which is taken from p.100 of Carroll’s book (click for larger version). This shows various sets of data from a study by a team led by Abdul-Halim Salem at the University of Utah, in which a thick gel has been used to separate DNA of different sizes. The presence of a SINE leads to the DNA in some species being longer than equivalent genes in other species which lack that SINE.
So the first set of data shows a SINE which is specific to humans. But the second shows a SINE that is shared by humans, chimps and bonobos – evidence of common descent for the three species. And the third shows a SINE that is shared by all apes but not shared by monkeys.
Analysis of more than 100 SINEs enabled the researchers to produce the family tree for humans, apes and monkeys shown below (from p.101):
All I can say is I find this entirely persuasive beyond all conceivable doubt (unless we regard it as conceivable that God would deliberately engineer human DNA so as to create a misleading impression of common descent with other primates). It’s also one of the most interesting glosses I have ever read on the first clause of Genesis 2:7.