Sentence:  They propose that the brain manages <WSD>numerical</WSD> systems with circuitry that is equipped for action related to "more than-less than", "faster-slower", "nearer-farther", "bigger-smaller", computations of "any kind of stuff in the external world". This neural activity allows us to successfully reach, grasp, throw or point. Bueti and Walsh argue further that, "it is on these abilities that discrete <WSD>numerical</WSD> abilities hitched an evolutionary ride," given the primitive need to make these kinds of judgments of space and time. Number then, as a measure, is not primary — what comes first is our need to move accurately. 
Meaning of the word marked with <WSD> tags:  of or pertaining to numbers