The Flynn Effect — the observation that average IQ test scores are rising, and have been doing so, in many industrialised countries throughout the 20th century — has been known about for some time, and it’s been debated whether this is because people are actually getting more intelligent (whatever that means), or whether it’s just an artifact of how IQ tests are measured (e.g. in a society where people have more contact with IQ-test-like puzzles, you might expect their test scores to rise, without any corresponding rise in other cognitive abilities).
Matt McIntosh at Gene Expression notes that here has been physiological changes in the population over this time period which suggests the Flynn Effect corresponds to real increases in intelligence:
To my mind, the most compelling evidence in favor of Flynn Effect gains being real is physiological: it’s well known that there have been increases in height concurrent with increases in intelligence in all the countries where the FE has been operative. What’s less well known is that there have also been recorded increases in cranial capacity […] and in brain size.
Given an increase in brain size and the correlation between IQ and brain size (0.4), it’d be pretty remarkable if there wasn’t any corresponding increase in intelligence. Also, in support of Lynn’s nutrition hypothesis, there have been correlations found in developed countries between IQ and presence of certain micronutrients.
Also, there have been a few studies showing that FE gains tend to be disproportionately located at the left half of the curve rather than the right, which is the nutrition theory would predict given that the less bright people tend to be poorer and thus benefit more than the wealthier (who tend to be smarter) from nutritive improvements.
So there you have it — we really are cleverer than our ancestors.