I'm betting the latter. Consider that lead also tastes sweet[1], that's why kids would eat lead paint. Our ancestors were never placed in situations where eatin

I'm betting the latter. Consider that lead also tastes sweet[1], that's why kids would eat lead paint. Our ancestors were never placed in situations where eating either lead or heavy water could change evolutionary outcomes because these substances are not easily obtained in high concentrations in nature. [1] https://www.thoughtco.com/sugar-of-lead-3976065 https://www.thoughtco.com/sugar-of-lead-3976065