Negative Selection Is Not What Darwin Wanted
Darwin wanted to explain humans from bacteria. He can’t get there by just protecting what bacteria already had.
The tuatara is a rare lizard that only survives on certain islands off the south island of New Zealand. It’s a ‘living fossil’ – the “Sole survivor of a once-diverse lineage,” Jones and Hutchinson write in Nature. It’s a reminder that evolution includes a strong tendency to go extinct. Somehow, this sole surviving member of Rhynchocephalia found a niche where it could survive.
In the same issue of Nature, Philip Ball reviews a book that compares cities to organisms. But cities are intelligently designed; they are not subject to biological mutation and natural selection.
Negative selection against deleterious alleles produced by mutation influences within-population variation as the most pervasive form of natural selection.
In Science, ten authors from two consortia discuss how “Negative selection in humans and fruit flies involves synergistic epistasis.” Basically, this means that organisms work hard to rid themselves of bad mutations. Negative selection predominates, they say. We can all be thankful that our bodies try to protect us from harmful mutations, but how did bacteria climb up to humanity that route? One cannot climb Mt. Improbable by trying to stay on the same stair in a howling wind.
Negative selection against deleterious alleles produced by mutation influences within-population variation as the most pervasive form of natural selection. However, it is not known whether deleterious alleles affect fitness independently, so that cumulative fitness loss depends exponentially on the number of deleterious alleles, or synergistically, so that each additional deleterious allele results in a larger decrease in relative fitness. Negative selection with synergistic epistasis should produce negative linkage disequilibrium between deleterious alleles and, therefore, an underdispersed distribution of the number of deleterious alleles in the genome. Indeed, we detected underdispersion of the number of rare loss-of-function alleles in eight independent data sets from human and fly populations. Thus, selection against rare protein-disrupting alleles is characterized by synergistic epistasis, which may explain how human and fly populations persist despite high genomic mutation rates.
Science Daily‘s summary of the paper in Science, referenced above, discusses “Ongoing natural selection against damaging genetic mutations in humans.” The authors admit to an idea very similar to John Sanford’s classic, Genetic Entropy and the Mystery of the Genome. He claimed that humans pass on so many neutral mutations, the human population is more likely to go extinct than improve by rare ‘beneficial’ mutations, if there are any. This article echoes that concept:
The survival of the human species in the face of high rates of genetic mutations has remained an important problem in evolutionary biology. While mutations provide a source of novelty for the species, a large fraction of these genetic changes can also be damaging. A newborn human is estimated to have ~70 new mutations that the parents did not have. In a project conducted by Brigham and Women’s Hospital research geneticist Shamil Sunyaev, PhD, and University of Michigan professor Alexey Kondrashov, PhD, scientists studied natural selection in humans. Their findings are published in a new paper in Science, where they report that, as a species, humans are able to keep the accumulation of damaging mutations in check because each additional mutation that’s added to a genome causes larger, and larger consequences, decreasing an individual’s ability to pass on genetic material.
This “long-standing conundrum in evolutionary biology” is only mitigated, not overcome, by a shuffling maneuver: sex. “[S]ex had to come about in a species such as our own to allow for more effective natural selection because the mutation rate is too high to sustain otherwise.” If that constitutes an “evolutionary advantage,” it is not one poised to help an organism grow wings or eyes. “This observation is general and is not limited to the human species,” they point out. So how is Mr. Darwin supposed to coax that bacterium up Mt. Improbable, where humanity is waiting to be invented?
We highly recommend Genetic Entropy by Cornell geneticist Dr. John Sanford. It will cure you of Darwinism once and for all. It will also reinforce the Biblical view that things are running down, not up, since the Creation and the Fall.