The collective intellect is change-blind. Knowledge gained seems so natural that we forget what it was like not to have it. Piaget says children gain long-term memory at age 4 and don't learn abstract thought until ten; do you remember what it was like not to have abstract thought? We underestimate our intellectual progress because every every sliver of knowledge acquired gets backpropagated unboundedly into the past.

For decades, people talked about "the gene for height", "the gene for intelligence", etc. Was the gene for intelligence on chromosome 6? Was it on the X chromosome? What happens if your baby doesn't have the gene for intelligence? Can they still succeed?

Meanwhile, the responsible experts were saying traits might be determined by a two-digit number of genes. Human Genome Project leader Francis Collins estimated that there were "about twelve genes" for diabetes, and "all of them will be discovered in the next two years". Quanta Magazine reminds us of a 1999 study which claimed that "perhaps more than fifteen genes" might contribute to autism. By the early 2000s, the American Psychological Association was a little more cautious, was saying intelligence might be linked to "dozens – if not hundreds" of genes.