https://slatestarcodex.com/2020/01/13/2019-adversarial-collaboration-winners/

Thanks to everyone who participated and/or voted in the 2019 Adversarial Collaboration Contest. And the winner is…

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Adrian Liberman and Calvin Reese, for Does Calorie Restriction Slow Aging?.

An extraordinarily close second place (26.9% vs. 26.2% of votes) goes to David G and Froolow, for Is Eating Meat A Net Harm?