Immortality has a specific meaning here, which is that risk of death due to intrinsic causes does not increase over time. This is distinct from negligible senescence, which is more a case of few manifestations of aging until very late life.<p>Immortality seems to be the case for hydra, for example. (<a href="http:&#x2F;&#x2F;www.ncbi.nlm.nih.gov&#x2F;pubmed&#x2F;22689361" rel="nofollow">http:&#x2F;&#x2F;www.ncbi.nlm.nih.gov&#x2F;pubmed&#x2F;22689361</a>)<p>Immortality is also observed for flies in late life (<a href="http:&#x2F;&#x2F;discovermagazine.com&#x2F;2001&#x2F;may&#x2F;breakdialogue" rel="nofollow">http:&#x2F;&#x2F;discovermagazine.com&#x2F;2001&#x2F;may&#x2F;breakdialogue</a>). They have a very high mortality rate at that point, but it doesn&#x27;t increase further over time. That doesn&#x27;t seem to be the case for humans, though, based on the very sparse data for people at extreme old age.