A contested study suggests the ability to embed sequences within other sequences, a skill called recursion and crucial to grammar, has ancient roots.

A multi-institutional research team found the cognitive ability to represent recursive sequences occurs in humans and non-human primates across age, education, culture and species.

YULIN CAO, G. LADAS, SYMMETRIC PERIODIC SOLUTIONS OF RATIONAL RECURSIVE SEQUENCES, The Rocky Mountain Journal of Mathematics, Vol. 25, No. 1 (WINTER 1995), pp. 133-143 ...