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Equation 6 · Part 2 · Human Evolution Did Not Stop, and Medicine Is Now Steering It

Symbol q_n

qn+1=qn/(1+qn)≈0.009901q_{n+1} = q_n/(1+q_n) \approx 0.009901
qnq_n

What this part means

qnq_n is one of the signed contributions combined to compute the quantity on the left.

Its job in the formula

qnq_n is one of the signed contributions combined to compute the quantity on the left.

The passage around this formula

Set s = 1 , the theoretical maximum in which every affected embryo is detected and never implanted: for q = 0.01 , this gives qn+1q_{n+1} = qnq_n/(1+qnq_n) ≈\approx 0.009901 , a reduction of under one-tenth of one percent of the allele’s frequency in a single generation, even at total, universal, perfectly effective screening. The reason the effect is so small is structural, not a modeling artifact: for a rare recessive allele, the overwhelming majority of copies are carried silently in heterozygous carriers, invisible to any selection that acts only on homozygotes, and embryo selection — like natural selection against recessive disease before it — can only ever act on the small fraction of matings…

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