Some evolutionary biologists think—incorrectly, in my opinion—that molecular biology has made no contributions to our understanding of evolution.
PNAS published a series of articles on Gregor Mendel and one of them caught my eye. Here's what Nicholas Barton wrote in his article The "New Synthesis".
During the 1960s and 1970s, there were further conceptual developments—largely independent of the birth of Molecular Biology during the previous two decades (15). First, there was an understanding that adaptations cannot be explained simply as being “for the good of the species” (16, 17). One must explain how the genetic system (including sexual reproduction, recombination, and a fair meiosis, with each copy of a gene propagating with the same probability) is maintained through selection on individual genes, and remains stable despite mutations that would disrupt the system (17, 19, 20). Second, and related to this, there was an increased awareness of genetic conflicts that arise through sexual reproduction; selfish elements may spread through biased inheritance, even if they reduce individual fitness (19, 21, 22). In the decade following the discovery that DNA carries genetic information, all the fundamental principles of molecular biology were established: the flow of information from sequences of DNA through RNA to protein, the regulation of genes by binding to specific sequences in promoters, and the importance of allostery in allowing arbitrary regulatory networks (23, 24). Yet, the extraordinary achievements of molecular biology had little effect on the conceptual development of evolutionary biology. Conversely, although evolutionary arguments were crucial in the founding of molecular biology, they have had rather little influence in the half-century since (e.g., ref. 25). Of course, molecular biology has revealed an astonishing range of adaptations that demand explanation—for example, the diversity of biochemical pathways, that allow exploitation of almost any conceivable resource, or the efficiency of molecular machines such as the ribosome, which translates the genetic code. Technical advances have brought an accelerating flood of data, most recently, giving us complete genome sequences and expression patterns from any species. Yet, arguably, no fundamentally new principles have been established in molecular biology, and, in evolutionary biology, despite sophisticated theoretical advances and abundant data, we still grapple with the same questions as a century or more ago.
This does not seem fair to me. I think that neutral theory, nearly neutral theory, and the importance of random genetic drift relied heavily on work done by molecular biologists. Similarly, the development of dating techniques using DNA and protein sequences is largely the work of molecular biologists. It wasn't the adaptationists or the paleontologists who discovered that humans and chimpanzees shared a common ancestor 5-7 million years ago and it wasn't either of those groups who discovered the origin of mitochondria.
And some of us are grappling with the idea that most of our genome is junk DNA, a question that never would have occurred to evolutionary biologists from a century ago.
Barton knows all about modern population genetics and the importance of neutral theory because later on he says,
If we consider a single allele, then we can see it as “effectively neutral” if its effect on fitness is less than ∼1/2Ne. This idea was used by Ohta (54) in a modification of the neutral theory, to suggest why larger populations might be less diverse than expected (because a smaller fraction of mutations would be effectively neutral), and why rates of substitution might be constant per year rather than per generation (because species with shorter generation times might tend to have large populations, and have a smaller fraction of effectively neutral mutations that contribute to long-term evolution). Lynch (21) has applied this concept to argue that molecular adaptations that are under weak selection cannot be established or maintained in (relatively) smaller populations, imposing a “drift barrier” to adaptation. Along the same lines, Kondrashov (55) has argued that deleterious mutations with Nes ≈ 1 will accumulate, steadily degrading the population. Both ideas seem problematic if we view adaptation as due to optimization of polygenic traits: Organisms can be well adapted even if drift dominates selection on individual alleles, and, under a model of stabilizing selection on very many traits, any change that degrades fitness can be compensated.
Barton may think that the drift-barrier hypothesis is "problematic" but it certainly seems like a significant advance that owes something to molecular biology.
What do you think? Do you agree with Barton that, "... the extraordinary achievements of molecular biology had little effect on the conceptual development of evolutionary biology."
