Natural Selection Applied to Humans

Since Charles Darwin wrote Origin of Species, many scientists have viewed natural selection as one of the most influential mechanisms of change.  However, many scientists argue that natural selection has done little in humans to produce new traits. In this, they are correct, but not for the reasons they expect. In this article, we will walk through why natural selection cannot improve humanity, on either a creationist or an evolutionist perspective.

A few caveats upfront about the scenario we are about to walk through. I have implicitly assumed that the evolutionary story is true and worked out the data accordingly. Essentially I am performing an internal critique of evolutionary dogma. I am using their own data and assuming their own paradigm to demonstrate why their paradigm is impossible.

A quick dive into the literature on natural selection in humans enlightens us as to why natural selection and mutation cannot improve humans. This is based on human generation time and the rate of human mutations. The human generation interval historically was somewhere between 26-33 years (Moorjani et al, 2016).  Since selection is based on differential reproduction in the evolutionary paradigm, the age of reproduction will impact the ability of selection to fix new variants.  According to a 2012 study, humans and Neanderthals split a mere 400,000-800,000 years ago (Langergraber et al, 2012).  Simple division allows us to derive a range of possible generations that have taken place since the human/Neanderthal split.  The numbers are as follows: a minimum of 15, 385 generations and a maximum of 30,769  generations since humans split from Neanderthals (Side note, Neanderthals were completely human. But, for the sake of the argument, we are assuming they were not). Both of these numbers are best-case scenarios for evolution which assume the age of first reproduction is 26. The numbers would undoubtedly be lower if a higher age of reproduction is assumed.

Being that there are a lot of generations between Neanderthals and humans, it is surprising that selection has not greatly improved the human genome, except for selection being incredibly slow. JBS Haldane proposed that selection would take 300 generations to fix a new gene in a population (Haldane, 1957), a number confirmed by more recent studies (Woodruff et al, 2004). Again simple division can give us a rough estimate of how many chances natural selection has had to improve the human genome, assuming the evolutionary paradigm is true. Based on the above-derived numbers, roughly 51-102 new genes could have become fixed since humans split with Neanderthals.  While researchers have yet to determine the exact number of genes in a single human’s genome, current estimates are around 22,000 odd functional genes (Salzburg, 2018). Even if we ignore “functionless” genes (side note, the ENCODE project demonstrated much more of the genome is functional than this, but we are assuming the evolutionary scenario is correct. Were we to include all the genes ENCODE found to be functional, the problem would be much worse), the human genome is significantly larger than the number of genes that natural selection and genetic drift could have fixed since the human/Neanderthal lineage break.  There simply has not been enough time.

This problem gets worse if we start including human mutation rates. Numerous human mutation rates have been measured. For our purposes, we will use a slightly faster one, 1.20×10^-8 per nucleotide per generation(Eichler et al, 2012). This leads to about seventy-seven new mutations per person, per generation. Of those, based on neutral theory, about 4 are deleterious in the sense of causing an obvious clinical malfunction (Giannelli and Green, 2000).  Neutral theory assumes that beneficial mutations are so small as to be incalculable (Kimura, 1986). Therefore the remaining seventy-three new mutations are neutral or very close to neutral. Only these mutations are eligible for fixation.

Based on the number of generations we derived above, humans should have undergone anywhere from 1,123,105 to 2,246,137 mutations since the split from Neanderthals according to the evolutionary timescale. The human genome is 6.4 billion nucleotides long.  There simply have not been that many changes in proportion to genome size. Worse, more than one gene needs to be changed to affect the trait. Hair color is controlled by at least eleven genes (Kayser et al, 2011). Taking that number as a baseline and assuming that it takes at least ten mutations to change generate new functions in each gene (a conservative figure most likely), a maximum of 20,419 genes could have acquired new functions in the evolutionary timescale. However, because of the slow pace of selection, 99.5% of these changes simply vanish. Only 102 could possibly be fixed.

Hopefully, you see the problem here.  Evolution simply cannot generate enough stable variation fast enough to split humanity from the Neanderthals. Evolution might be able to fix a single mutation change, like that for blond hair or blue eyes, but large scale physiological changes are impossible. Time has gone from being the evolutionists’ hero to their worst enemy. Population genetics forbids any possibility of evolution occurring.

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References

Eichler EE, et al. 2012. Estimating human mutation rate using autozygosity in a founder population. Nature Genetics 44 (11):1277-1281.

Gianelli F, Green PM. 2000. The X chromosome and the rate of deleterious mutations in humans. Am J Hum Gen. 67(2):515-517.

Haldane, J.B.S. 1957. The cost of natural selection. J. Genet.  55. 511-524.

Kayser M, et al. 2011. Model-Based prediction of human hair color using DNA variants” Human Genetics 129:443-454,

Kimura M. 1986. DNA and the neutral theory. Phil Trac R Soc Lond B. 312(1154):343-354.

Langergraber, K.E. Prüfer, K. Rowney, C. Boesch, C. Crockford, C. Fawcett, K. Inoue, E. Inoue-Muruyama, M. Mitani, J.C. Muller, M.N. et al.2012. Generation times in wild chimpanzees and gorillas suggest earlier divergence times in great ape and human evolution. Proc. Natl. Acad. Sci. U.S.A. 109(39):15716-15721.

Moorjani, P. Sankararaman, S. Fu, Q. Przeworski, M. Patterson, N.  Reich, D. 2016. A genetic method for dating ancient genomes provides a direct estimate of human generation interval in the last 45,000 years. Proc. Natl. Acad. Sci. U.S.A. 113 (20): 5652-5657.

Salzburg, S.L. 2018. Open questions: how many genes do we have?. BMC Biol. 16(94).

Woodruff, R.C. Thompson, J.N. Gu, S. 2004. Premeiotic clusters of mutations and the cost of natural selection. J Hered. 95(4):277-283.