Why do we differ in number sense? Evidence from a genetically sensitive investigation

Area of Science:

• Cognitive genetics
• Developmental psychology
• Behavioral genetics

Background:

• Number sense, the ability to estimate quantity, is present in animals and humans.
• Individual differences in human number sense emerge early and correlate with general intelligence.
• The genetic and environmental origins of these individual differences remain largely unknown.

Purpose of the Study:

• To investigate the genetic and environmental influences on individual differences in number sense.
• To conduct the first large-scale, genetically sensitive study on number sense in twins.
• To explore the potential role of evolutionary selection in shaping number sense heritability.

Main Methods:

• Assessed numerosity discrimination abilities in 837 monozygotic and 1422 dizygotic twin pairs.
• Utilized univariate genetic analysis and sex-limitation models.
• Performed Genome-wide Complex Trait Analysis (GCTA) on 1118 unrelated individuals with genetic data.

Main Results:

• Number sense showed moderate heritability (32%), primarily influenced by non-shared environmental factors (68%).
• No significant sex differences were found in the etiology of number sense.
• GCTA revealed effectively zero heritability for number sense, contrasting with other cognitive abilities.

Conclusions:

• Individual differences in number sense are largely shaped by environmental influences rather than shared genetics.
• The discrepancy between twin and GCTA heritability estimates supports the hypothesis of reduced additive genetic variance due to directional selection.
• Number sense may represent an evolutionarily important trait where genetic variation has been minimized.