1. Most limb anomalies are from non-heritable fetal injuries. 2. The 5-digit design is older than the primates, and hard to change without breaking something, so 3. Heritable missing or extra digits are usually parts of syndromes featuring serious problems, e.g. heart, metabolic, or brain defects. 4. Exception: Some ectrodactylies, but then the actual limb defects are severe enough to impact reproductive probabilities. 5. The detailed topological equivalence yet functional inequivalence of hands and feet needs to be explained. The present design of toes as ridiculous parodies of fingers, right down to fourteen phalanges and nails, confers no advantage over a simple flexible tab, like being born with socks on. (Except for people without hands.) 6. The 14-phalanx, opposable thumb design was optimized over a long time by our tree-dwelling ancestors. Toes are just vestigial fingers, catagenetic to the point of diminishing returns. Aside: I've never seen convincing evidence that, even in those rare cases of complete duplication of a metacarpal ray and forearm machinery, extra fingers can move independently. (Except for depressing medical articles admitting that it's sometimes hard to decide which childish finger to amputate.) Is the infant brain plastic enough to build drivers for nonstandard hardware? Especially interesting would be those cases of "mirror hand" (dimelia. Very rare.) --rwg