The introduction was setting up an apparent contradiction to be resolved later. It’s obvious that any apparent contradiction must have a way of being resolved.
Walking and swimming animals don’t have near-zero benefit from sensing magnetic fields. And some of them—but only a fraction—do have some (seemingly less-accurate) way of sensing magnetic fields.
Primates have 2 arms and 2 legs because they evolved from animals with 4 legs and bilateral symmetry.
The introduction was setting up an apparent contradiction to be resolved later. It’s obvious that any apparent contradiction must have a way of being resolved.
Walking and swimming animals don’t have near-zero benefit from sensing magnetic fields. And some of them—but only a fraction—do have some (seemingly less-accurate) way of sensing magnetic fields.
Primates have 2 arms and 2 legs because they evolved from animals with 4 legs and bilateral symmetry.