A mutation that causes a human have 11 toes is (neutral, harmful, or beneficial.)

Having an extra toe or finger is not harmful at all, it is an uncommon chance for babies to be born with an extra toe or finger but most of the time it is amputated soon after the birth. It can't cause any harm. Though some scientists believe it could be beneficial for some stuff, such as tying a shoe with only one hand. Or playing numerous games at once. Though I would go with neutral.

P. S

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-Faker/Tosrel