Le Fanu devotes a chapter to the mystery of the Double Helix. Despite the extraordinary accomplishment of the Human Genome project, we are still unable to determine how genetic code causes one creature to be a fly while another becomes a human. Le Fanu detailed the ways in which uncovering the human gene sequence led to highly unexpected findings and more questions than answers. Not only were there fewer genes than expected, but 95% of the Double Helix was "junk." It was not clearly obvious how our sparse number of information bearing genes made us human. Additionally, studying mutations that lead to genetic disease resulted in the discovery that multiple mutations could cause a given disease. Even more puzzling was the finding that mutations could be present without always exerting their effect. Genes, we now know, are multi-tasked and work in concert with other genes. They are capable of displaying contradictory properties, depending on context and can be "essential for, and yet irrelevant to" their purpose. These findings make the concept of natural selection with random mutation appear simplistic and untenable. A discovery which has shed some light on the complex functioning of genes is the master genes, or Hox genes. They function as a switch, turning off and on various genes. However, scientists are learning that the same Hox genes which are responsible for a particular outcome in one organism produce a different outcome in another. So, the question remains, how does a fly know to be a fly and a mouse know to be a mouse? What is controlling the master genes, which are controlling everything else? The current assumption is that the Hox genes "turn the genes of the universal toolkit 'on and off' in a different sequence and at different times to produce these different structures."
However, Le Fanu has a problem settling with this explanation. He states that "the parts of the fly-its eyes, wings and limbs-are all 'of a piece', and it is difficult again to conceive how the relevant master gene for each could have chanced upon the correct sequence of switches to generate the appropriate part. It is as if the 'idea' of the fly (or any other organism) must somehow permeate the genome that gives rise to it, for it is only through the master genes of the embryonic fly's knowing it is a fly that they will activate that sequence of switches that will give rise to those appropriate structures."
He concludes that "there must be some non-material formative influence that, from the moment of conception, imposes the order of form on the developing embryo...and holds it constant while its cells and tissues are continually renewed...."
I appreciate the chapter for educating me on the incredible complexity of DNA. He does a terrific job of highlighting the questions and mystery that continue to pervade the study of the human body and our evolution. However, I'm not sure that I can accept his conclusion that there can be no material explanation for the workings of the Hox genes. It appears suspiciously like a God-of-the-Gaps argument that is subject to burial as science fills in the holes. I would agree if he ended the chapter by merely pointing to the appearance of a mastermind determining various forms, but I'm wary of his conclusion that sounds like a spirit inhabits fertilized eggs to ensure they grow up to be what the spirit intends.