Pronoun problems

pronoun problems
The passage below is from ‘the Blank Slate’ by Steven Pinker.

http://evolbiol.ru/blankslate/blankslate.htm

That representation feeds other circuits that make sense of the world by imputing causes to events and placing them in categories that allow useful predictions. And that sense-making, in turn, works in the service of motives such as hunger, fear, love, curiosity, and the pursuit of status and esteem. As I mentioned, abilities that seem effortless to us — categorizing events, deducing cause and effect, and pursuing conflicting goals — are major challenges in designing an intelligent system, ones that robot designers strive, still unsuccessfully, to duplicate.

In this passage, I’m not sure what the underlined pronoun, ‘ones’ stands for.
It seems to refer to ‘an intelligent system’ in the sense of meaning, but the problem is that there seems to have a disagreement between ‘an intelligent system’ and ‘ones.’

Hope for your replies.
Regrads.