Junk DNA deniers and Darwin Day

Is it is logically possible to accept the science of evolutionary biology and still deny the existence of junk DNA? I’m not sure.

It is OK (though unfortunate) to be a biologist who is wrong in their assessment of an evolutionary topic. This is not a rejection of the mechanisms and rationale of evolution in the way that some reject the existence of junk DNA for purely religious reasons. Most modern rejections of junk DNA instead ignore evolution in its proper sense, even though it is central to their argument, and invoke hypothetical genetic-adaptation scenarios instead.

Evolutionary biologist Ernst Mayr used to talk about ‘the geneticists‘ like they were a rival warring tribe, but I’ve never seen a closer match in the whole of science than between contemporary geneticists and evolutionary biologists. Its hard to work in genomics without speaking evolution, and vice versa. If you are interested in the existence and nature of junk DNA then you need to read broadly in the field of molecular evolution, the fully grown-up child of genetics and evolution. Its OK for anyone to speculate about the forces creating and maintaining junk DNA, but if you don’t know the literature of the field actually studying junk DNA then it’s just fun ‘pub banter’.

What those who don’t read on molecular evolution usually assume is that junk DNA is defined by a lack of current knowledge of function. Instead it involves decades of theory, data collection, model testing and refinement into a detailed and exceptionally well-substantiated discipline.

I think Darwin would have loved junk DNA, and have written eloquently about the chromosomal tangled bank inhabiting our nuclei. The original tangled bank quote, from Origin of Species, always makes me pleasantly surprised about the big-picture nature of Darwin’s thoughts, and the modernity of thinking in terms of Laws.

…have all been produced by laws acting around us. These laws, taken in the largest sense, being Growth with reproduction; Inheritance which is almost implied by reproduction; Variability from the indirect and direct action of the conditions of life, and from use and disuse; a Ratio of Increase so high as to lead to a Struggle for Life, and as a consequence to Natural Selection, entailing Divergence of Character and the Extinction of less improved forms. 

Evolution and natural selection are not synonyms, and accepting the monumental, overwhelming, evidence for evolution means understanding all its component forces, even those like mutation and drift that are not particularly concerned with function and adaptation. Drift, mutation, recombination, gene flow, and selection all shape the evolution of genomes, and if you want to read the full story of evolution you need to read broadly in regions of the genome without function. Fortunately for us, that’s most of it.

Happy Darwin Day!


Notes:

If you want to start reading about junk DNA I recommend Larry Moran’s blog, Sandwalk, especially his junk DNA required reading list and Five Things You Should Know if You Want to Participate in the Junk DNA Debate. Also Michael Lynch’s book “The Origins of Genome Architecture” (2007 ISBN-10: 9780878934843) is very worthwhile indeed.

Featured image: Onion sellers and The Onion Test (Gregory 2007) ‘The onion test is a simple reality check for anyone who thinks they have come up with a universal function for non-coding DNA. Whatever your proposed function, ask yourself this question: Can I explain why an onion needs about five times more non-coding DNA for this function than a human?’

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