Arguments for symbolic communication needed for reciprocal altruism - again dubious. Extended discussion of probable early symbolic communication. Not language as we know it. Heavy on ritual activity which is important in establishing symbolic references. Extensive use of gestures, equivalents of dance.
Some animals have modest symbolic learning capability.
Humans have evolved a major restructuring of the brain to enchance symbolic learning. Language acquistion had to become fail-safe. After 2 million years it has clearly reached this status. The simplest way to make something fail-safe is to design it far beyond the basic requirements. We are not just adapted for symbol learning, but for fail-safe symbol learning.