Biology / Unit 8 Bio 1679 short lesson, about 20 seconds
Variation Precedes Selection
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The idea
Selection only chooses among existing variation, correcting the twin misconception at Bio 1677; it cannot create a needed trait from scratch.
In practice
A drought does not generate a new drought-tolerance allele — it only changes which existing alleles, if any, spread through survivors.
Where people slip
Mutations do not arise because a population needs them — they occur randomly, before any pressure appears, useful or not.
Your place on the trail
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Unlocks
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