Earlier this month, when the biotech firm Human Longevity published a controversial paper claiming that it could predict what a person looks like based on only a teeny bit of DNA, it was just a little over a week before a second paper was published discrediting it as flawed and false. The lightening speed with which the rebuttal was delivered was thanks to bioRxiv, a server where scientists can publish pre-prints of papers before they have gone through the lengthy peer-review process. It took only four more days before a rebuttal to the rebuttal was up on bioRxiv, too.