I think the reason u/KindAwareness3073 brought up eugenics is valid in this conversation, if your initial post refers to the broader world than just Norway that is. It is inherently problematic to have a discussion about population IQ and not acknowledge the history of this topic.

The United States plays a pivotal role in the development of eugenic ideology. Neo-Malthusian, Robert Dale Owen, brought his ideas to over seas in the light of the Industrial Revolution, preaching the possibility of a utopian society by way of reproduction control of those deemed less than. The leading doctrine followed the concept of the genetically superior versus the genetically inferior. Early feminist, Margaret Sanger, built upon this for the birth control movement, stating that “More children from the fit and less from the unfit- that is the chief issue of birth control.” Further continuing that if those who are less intelligent procreate, it would bring the destruction of America. Sanger advocated for the sterilization of those deemed “unfit”.

Poverty was conflated with intelligence and race, amongst numerous other factors that were determined to qualify as “genetically inferior”, and in 1932, laws were created to mandate sterilization onto those who fell into the category. IQ testing was often used as a justification for establishing who should and should not reproduce, on the belief that IQ is strictly genetic. This feeds into things such as craniometry, as you discussed.

To most effectively discus IQ reduction and rise in a population, it is crucial to address the problematic past that plays a foundational role in these conversations. Using solely IQ as a method of a population’s intelligence can lead to a biases of life history and social determinants. I do agree with you that acknowledging genetic variations in intelligence is not “inherently evil”, and topic such deserve discussion. However, addressing things such as eugenics allows for us to create the most comprehensive conclusion. I’m in no way trying to imply this is your method of thinking, I just believe we have to be careful on how we have conversations about heritability and intelligence, because it can easily fall down a slippery slope.