The fundamental problem with all these denials is that it is impossible to prove a negative. This is no minor issue. When anyone claims the absence of a given capacity in other species, and speculates that it must therefore have arisen recently in our lineage, we hardly need to inspect the data to appreciate the shakiness of such a claim. All we can ever conclude with some certainty is that we have failed to find a given skill in the species that we have examined. We cannot go much further than this, and we certainly may not turn it into an affirmation of absence. Scientists do so all the
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