Final answer:
The likely explanation for the observed decrease in women's IQs after age 60 when comparing different birth cohorts is the cohort effect, which includes various socio-cultural changes that can impact intelligence measures. Fluid intelligence declines in late adulthood, but engaging in mental and physical activities has been shown to help mitigate this decline.
Step-by-step explanation:
Concerning the observation that after age 60, women's IQs drop dramatically based on comparisons between women born in different eras (1910-1930 vs. 1960-1980), it is likely that cohort effects significantly influence the observed differences. These effects can include changes in education, health, and socio-economic status over time that impact cognitive abilities. For instance, the Flynn effect demonstrates that successive generations score higher on IQ tests, not necessarily due to enhanced intelligence but potentially due to these cohort effects. It's also important to recognize that while fluid intelligence (including processing abilities, reasoning, and memory) can decline in late adulthood, crystallized intelligence (knowledge and skills gained through experience) may remain stable or improve. Factors such as mental and physical activity have been shown to help delay cognitive decline and reduce the incidence of mild cognitive impairment and dementia.