From: rokimoto557@gmail.com   
      
   On 12/15/2025 6:53 PM, MarkE wrote:   
   > Larry Moran offers this analysis:   
   >   
   > "...A small number of these neutral mutations will become fixed in the   
   > population and it's these fixed mutations that produce most of the   
   > changes in the genome of evolving populations. According to the neutral   
   > theory of population genetics, the number of fixed neutral mutations   
   > corresponds to the mutation rate. Thus, in every evolving population   
   > there will be 100 new fixed mutations per generation. This means that   
   > fixation of 22 million mutations would take 220,000 generations. The   
   > average generation time of humans and chimps is 27.5 years so this   
   > corresponds to about 6 million years. That's close to the time that   
   > humans and chimps diverged according to the fossil record. What this   
   > means is that evolutionary theory is able to explain the differences in   
   > the human genome—it has explanatory power."   
   > https://sandwalk.blogspot.com/2025/12/how-many-regulatory-sites-in-   
   > human.html   
   >   
   > However, chimp to human evolution involves major (profound) adaptations,   
   > including:   
   >   
   > - Bipedalism and capacity for long-distance walking and endurance   
   > running: short, broad pelvis; S-shaped spine; long legs relative to   
   > arms; arched feet with non-opposable big toe.   
   >   
   > - Cognitive capacity increase: larger cranial capacity; dramatically   
   > expanded neocortex; highly developed prefrontal cortex; these produce:   
   > abstract reasoning; symbolic language; long-term planning; mathematics,   
   > music, art; large cooperative societies; etc.   
   >   
   > - Other physiology: extended childhood and adolescence; long lifespan;   
   > high energy investment in brain development; reduced muscle mass   
   > relative to body size; craniofacial morphology supporting speech   
   > articulation and dietary flexibility; precision hand grip and fine motor   
   > control.   
   >   
   > How many non-neutral adaptive mutations (in fact, highly adaptive,   
   > complex and coordinated suites of mutations) are required, over and   
   > above the estimated neutral/near-neutral mutations, to produce these   
   > adaptations, and how are these accounted for in the time available?   
   >   
      
   You likely missed the point.  Most (nearly all) of the genetic changes   
   between chimps and humans are due to neutral mutations that don't change   
   the organism enough to have been selected for or against, and the number   
   is within the bounds of neutral theory.  The phenotypic difference   
   between chimps and humans are believed to be due to only a small   
   fraction of the genetic differences between chimps and humans.  To   
   account for your "profound" differences doesn't take that many   
   mutations.  Nearly all the differences we observe in coding sequence are   
   neutral mutations because they do not change the amino acid sequence of   
   the protein or the amino acid substitution doesn't seem to affect the   
   function of the protein.  There are a lot more amino acid substitutions   
   segregating within the human population than there are that are   
   different between chimps and humans.  These variants usually do not have   
   much of a noticeable phenotype, but some of them like Sickle cell, Tay   
   Sachs, and cystic fibrosis may have some type of heterozygote advantage   
   and are segregating at relatively high frequency among humans even   
   though they are deleterious as homozygotes.   
      
   What Moran is pointing out is that the genetic changes that have evolved   
   between chimps and humans are all within the bounds of what it would   
   have been possible to select for in order to produce the phenotypic   
   differences between the two species.  We think that most of the   
   differences between chimps and humans are due to regulatory sequence   
   changes.  The genes are the same, but how they are regulated is different.   
      
   Ron Okimoto   
      
   Ron Okimoto   
      
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