Variation Precedes Selection
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Selection only chooses among existing variation, correcting the twin misconception at Bio 1677; it cannot create a needed trait from scratch.
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A drought does not generate a new drought-tolerance allele — it only changes which existing alleles, if any, spread through survivors.
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Mutations do not arise because a population needs them — they occur randomly, before any pressure appears, useful or not.
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- Nothing yet depends on this.