 A study in 2005 concluded that mothers teach the behavior to their daughters, and that all the sponge-users are closely related, suggesting that it is a fairly recent innovation.The calcium carbonate or silica spicules of most sponge genera make them too rough for most uses, but two genera, "Hippospongia" and "Spongia", have soft, entirely fibrous skeletons.Early Europeans used soft sponges for many purposes, including padding for helmets, portable drinking utensils and municipal water filters.