CoachHeredity is the transmission of traits from parents to offspring through reproduction — through, as Chapter 54 showed, two single cells. Traits that pass this way are hereditary: eye color and blood group are; scars and pierced ears are not, however long worn. The sorting test is the gametes: what two cells cannot carry, families cannot transmit.
Examples
Example 63.3 (Sorting a family album)
Grandfather’s photographs: his distinctive nose — hereditary, there it is again on the aunt and the cousin; his weathered farmer’s tan — acquired, his office-working grandson lacks it; his height — partly both, for the grandson overtops him on the same frame, fed by richer years (Proposition 18.1); his violin skill — not hereditary as skill (Example 60.6: synapses are trained, not transmitted), though the musical family tells us something subtler is at work in what is passed on: perhaps aptitude, never the trained wiring itself.