On The Evolutionary Origin of Symbolic Communication

The emergence of symbolic communication is often cited as a critical step in the evolution of Homo sapiens, language, and human-level cognition. It is a widely held assumption that humans are the only species that possess natural symbolic communication schemes, although a variety of other species can be taught to use symbols. The origin of symbolic communication remains a controversial open problem, obfuscated by the lack of a fossil record. Here we demonstrate an unbroken evolutionary pathway from a population of initially noncommunicating robots to the spontaneous emergence of symbolic communication. Robots evolve in a simulated world and are supplied with only a single channel of communication. When their ability to reproduce is motivated by the need to find a mate, robots evolve indexical communication schemes from initially noncommunicating populations in 99% of all experiments. Furthermore, 9% of the populations evolve a symbolic communication scheme allowing pairs of robots to exchange information about two independent spatial dimensions over a one-dimensional channel, thereby increasing their chance of reproduction. These results suggest that the ability for symbolic communication could have emerged spontaneously under natural selection, without requiring cognitive preadaptations or preexisting iconic communication schemes as previously conjectured.

online online). Note that this agent uses an indexical communication scheme.   Figure S3. Sample histories of additional evolutionary runs. Reproduction rates are shown with (green) and without (grey) communication enabled. The magnitude of the Pearson product-moment correlation coefficient between the top agent's position (y in red, x in blue) and ω out is also shown (see Methods    Figure S9. A flowchart of the protocol for the robotic experiments.

Supplementary Equations
The simplified and reduced evolved equation of the top agent from era 48 during run 7 is Communication has yet to emerge. Note that ω in does not appear anywhere in the agent's governing equations. This is the run analyzed in the main text.
The simplified and reduced evolved equation of the top agent from era 313 during run 7 is Indexical communication has emerged. This is the run analyzed in the main text.
The simplified and reduced evolved equation of the top agent from run 7 is Symbolic communication has emerged, see Supplementary Table S1 online. Example behaviors can be found in Figs. 2, 3 and Supplementary Fig. S4 online. This is the symbolic agent analyzed in the main text.
The simplified and reduced evolved equation of the top agent from run 1 is Symbolic communication emerged, see Supplementary Table S1 online. Example behaviors can be found in Supplementary  Fig. S5 online.
The simplified and reduced evolved equation of the top agent from run 5 is Symbolic communication emerged, see Supplementary Table S1 online.
The simplified and reduced evolved equation of the top agent from run 6 is Symbolic communication emerged, see Supplementary Table S1 online. Example behaviors can be found in Supplementary  Fig. S6 online.
The simplified and reduced evolved equation of the top agent from run 24 is Symbolic communication emerged, see Supplementary Table S1 online. Note that this simulation run was done with θ t measured relative to "north" (+y direction), instead of relative to "east" (+x direction). All other simulation details remain unchanged.
The simplified and reduced evolved equation of the top agent from run 33 is Symbolic communication emerged, see Supplementary Table S1 online. Note that this simulation run was done with θ t measured relative to "north" (+y direction), instead of relative to "east" (+x direction). All other simulation details remain unchanged.
The simplified and reduced evolved equation of the top agent from run 50 is Symbolic communication emerged, see Supplementary Table S1 online.
The simplified and reduced evolved equation of the top agent from run 70 is  Table S1 online.
The simplified and reduced evolved equation of the top agent from run 94 is θ t+∆t = − 3.43 y t − x t −3.39 y t + 4.07 y t + 4.63 y t + 4.38 y t −ω t in (S51) ω t+∆t out = y t + 3.39 y t + 3.96 y t + 6.51 y t − x t −3.96 y t + 4.73 y t − x t −3.48 y t + 5.31 y t + 4.11 y t + 3.65 y t −ω t in (S52) Symbolic communication emerged, see Supplementary Table S1 online. Example behaviors can be found in Supplementary  Fig. S7 online.
The simplified and reduced evolved equation of the top agent from run 81 is Symbolic communication did not emerge, this is an example of an agent that employs indexical communication, see Supplementary Table S1 online. Example behaviors can be found in Supplementary Fig. S8 online.