Another opposite of "natural" is "designed", and another opposite of artificial is "by chance".
"By chance" is also an accurate descriptor of natural intelligence.
Not sure if you were making a point, but your comment backs up the assertion that "natural" was a better choice than "real" in that sentence.
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1. Natural 2. Authentic 3. Genuine 4. Real 5. Organic 6. Original 7. Unaffected 8. Unpretentious 9. True 10. Sincere