Why do human hands have 5 fingers?

December 2022 · 2 minute read

Mark Changizi, an American neuroscientist, has developed a simple mathematical formula to explain the amount of an organism, from insects to mammals, even aliens. The name is the law of chi (Limb Law) .

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    • Changizi's formula is based on the length of the limbs and body radius. The amount of the organism (N) is calculated as follows:

    N≈2π / k.

  • L is the length of the genus.
  • R is the body radius.
  • k is the chi ratio, k = L / (L + R).

    • With this formula, the shorter the length of the limbs, the more accurate the result.

    Changizi tested the chi recipe with more than 190 species of organisms. The results show an amazing coincidence.

    With some special cases such as snakes, the length is zero, we have k = 0 and N is infinite. Thus, the snake is considered to have countless limbs but the length of chi is zero.

    Picture 1 of Why do human hands have 5 fingers?
    At the number of fingers on the human hand is not 4 or 6 but 5.

    For humans, we will apply the law of chi to the hand that explains why it has 5 fingers.

    The human hand has the length of the finger approximately the diameter of the palm. This means that the length of the finger is twice the radius of the palm.

    Apply to the formula we have:

    L ≈ 2R

    k ≈ L / [L + (L / 2)] = 2/3

    => N ≈ 2π / k ≈ 9.42

    The hand is not a separate creature, it attaches to the arm on nearly half of its circumference and the fingers can only grow from the other half of the circumference. Therefore, the number of fingers on one hand is 9.42 / 2 = 4.71, rounded to 5 fingers.

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