Let’s start with the good news: we’re getting brighter. Sadly, not individually as we age, but IQs have risen over time, with new generations having higher reasoning skill scores than their predecessors. This progress on abstract reasoning is in contrast to plateauing or declining scores for retained knowledge such as vocabulary.
Better nutrition or healthcare might explain some of this improvement. But there’s also been a greater focus on skills over knowledge by schools and parents. This was what Michael Gove was pushing against with his focus on children needing to learn basic facts.