IQ test for sperm donors: Questionable calculation with heritable intelligence

According to its statements, the Danish Donor Network is introducing mandatory IQ tests for sperm donors, the first sperm bank in Europe to do so. The results, along with a police clearance certificate, are intended to ensure greater transparency. The company justifies the move with the claim that a child's IQ is genetically determined “up to 80 percent.”

According to Donor Network, all donors undergo the “Culture Fair Test 20-R” (CFT 20-R). This standardized test is used to assess fluid intelligence, i.e., the ability for abstract and logical thinking, independent of acquired knowledge or linguistic skills.

The IQ test results will be transparently stored in the donor profiles, as will information on health history, family circumstances, and physical characteristics. In addition, all donors must provide a clean police clearance certificate. These measures are intended to provide recipients in Germany with more security and a better basis for decision-making. According to the company, Germany is considered one of the most important sales markets for Danish donor sperm.

Genetic inheritance as a sales argument

The central marketing argument is the statement that “up to 80 percent of a child's IQ” is genetically predetermined. However, studies show a much more differentiated picture: A meta-analysis by Florence A.R. Oxley and others from 2024 concludes that the heritable proportion of intelligence fluctuates between approximately 40 and 70 percent, depending on age and environmental conditions.

Furthermore, not only the donor but also the mother plays a significant role. Many genes involved in cognitive development are located on the X chromosome. Women have two of them, men only one—so a son's X chromosome always comes from the mother. This can give the maternal genetic material more weight.

However, not all intelligence-relevant genes are located on the X chromosome. Experts estimate that about 15 to 20 percent of genes related to neural and cognitive functions are located there, while the majority are distributed across other chromosomes. This is also shown by research papers on the influence of the X chromosome on the human brain and studies on X-chromosomal factors and cognition.

In addition, epigenetic mechanisms and genomic imprinting influence brain development. Certain genes are only activated if they come from a specific parent—an effect that, according to studies on genomic imprinting and brain functions and reviews on genomic imprinting in neural development, closely links to learning performance and neural plasticity. Factors such as education, nutrition, and emotional support also significantly influence the development of cognitive abilities, as comprehensive studies on environmental influences on cognitive development demonstrate.

(mack)