21 Essays on Infinite Lifespans   Michael R. Rose aquatic animal that used to be a staple of high school biol- ogy. Martinez found that his Hydra showed no substantial fall in survival rates over very long periods. They still died, but not in a pattern that suggested aging. Other scientists have gathered comparable data with small animals. [e.g. 3] Some species were immortal and some were not. The immortal spe- cies reproduced without sex. Also, invoking laws of thermodynamics as limits to life is clearly incorrect, given the evolutionary immortality of life forms. Such an invocation was always rankly amateur in any case, since these laws only apply to closed systems. Life on Earth is not a closed system. The earth receives an abundant input of energy from the sun. Thus, some of the deepest prejudices of professional biolo- gists concerning immortality are certainly false. Aging is not universal. There are organisms that are biologically immortal. However, this is not a very substantial conclusion. We knew enough about the biology of death decades ago to come to this finding. In a sense, what I have just described is the ‘old immortality’, the immortality that has always been with us. Below, I will describe a new immortality that has come into view only in the last decade or so. RECENT RESEARCH ON THE DEMOGRAPHY OF IMMORTALITY Another superstition of most biologists is that, once aging starts, it continues implacably until every organism is dead. But is aging implacable? In terms of mortality rates, we can re-state this question as whether or not aging species are subject to continually increas- ing  mortality  rates  throughout  adulthood.  A  deceleration in mortality was found first in human data. [4;5] Very old