Life tables had an early origin which may never be satis- 
factorily fixed. By the third century they included calculations of 
"life expectancy" (Trenerry 1926). Their crude revival in the 
seventeenth century by John Graunt at once demonstrated that mortality 
is high in the early years of human life and that regularity exists 
in vital phenomena superficially seeming to occur at random (Pearl 
191, p. 25). Their present detailed state of description for human 
populations is well known to most readers, and a review of it is 
beyond the scope of the present paper. 
No complete life table for a wild species appears to have 
been published until 1921 when Pearl and Parker reported on labora- 
tory studies of the fruit fly (Drosophila melanogaster). Biology 
still awaited the success of field workers in marking, aging, census- 
ing, and sampling wild populations. Fourteen years later, when Pearl 
and Miner (1935) reviewed the survival literature for the lower 
organisms, the house mouse (Mus musculus) was the only vertebrate to 
merit their attention. ou 
The dam was now ready to burst. During the next dozen 
years, fairly intensive survival studies were published on a number 
of fishes, on 5 species of mammals, and on at least 15 species of 
birds. This work has been the subject of a recent and excellent 
review by Deevey (1917), so that a summary of it need not be repeated 
here. The review, modestly entitled an introduction, condenses both 
vertebrate and invertebrade survival material into life tables which, 
for the first time, permit comparative studies of the vital statistics 
of natural populations. A few of its salient conclusions are worth 
noting here. 
"Both in nature and in the laboratory," writes Deevey (19h7), 
Kanimals differ characteristically in their order of dying." These 
differences in survival, he points out, conform to or approximate 
three types of survival curves predicted by Pearl and Miner (1935): 
Concave J-shaped survivorship lines.-~In mathematical 
parlance these are known as negatively skewed rectangular curves. 
They are believed to reflect the production of enormous numbers of 
eggs by a single female and extremely heavy mortality in the early 
stages of life. Although these curves undoubtedly are characteristic 
of many fishes and invertebrates, survival in the early stzges of 
life is extremely difficult to record in nature with any marked 
degree of accuracy. The only approach to this negatively skewed 
curve thus far reported for birds is found in Deevey's reanalysis 
of Nice's (1937) work on the song sparrow, 
Convex survival curves (positively skewed rectangular curves).--= 
These represent a high degree of survival throughout life and heavy 
mortality at the end of the species! life span. Under modern public~ 
health programs, man is changing his survival curve from the concave 
toward the convex type (Dublin and Lotka 1936). Dall bighorn sheep 
(Ovis dalli) studied by Murie (19h), the rotifer (Floscularia conifera) 
