Grandparents are the old farts of the family and parents of a person's father or mother – paternal or maternal. Every sexually-reproducing creature who is not a genetic chimera has a maximum of four genetic grandparents, eight genetic great-grandparents, sixteen genetic great-great-grandparents, etc., although the numbers will be lower in cases of pedigree collapse. In the history of modern humanity, around 30,000 years ago, the number of modern humans who lived to be grandparents increased exponentially. It is not known for certain what spurred this increase in longevity, but it is generally believed that a key consequence of three generations being alive together was the preservation of information which could otherwise have been lost; an example of this important information might have been where to find water in times of drought.