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Stanford scientists regrow lost cartilage and reverse arthritis in major breakthrough
(www.sciencedaily.com)
This is a most excellent place for technology news and articles.
Not a scientist, but from what I know it's all linked and proportional to a species' lifespan, so dogs are growing up faster, but also aging faster than humans in general. If a human reaches sexual maturity at 15, a dog does so at 1 or 2.