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I just came up with a great way to kill an hour on a Sunday afternoon. Ever wonder how fast paleo is growing, and whether it's still expanding like it used to? Well, I did a little study of my personal reference list for North American fossil mammals in order to answer the question. I'm assuming that the field as a whole doesn't differ in its behavior from this particular sub-sub-discipline. The data set includes 1536 references and is reasonably complete, although they get progressively more spotty the farther back before World War II you go. I excluded the 19th century completely because of this problem. I wrote a jiffy little C program to read the file and figure out how many references were published in each three year interval from 1900 on (data are appended for those who find such things entertaining). If you plot the data on a semi-log scale you'll see three interesting things. First, there is a generally exponential growth pattern, as indicated by straight-line fits of time to log(number of references). Second, there seem to be offsets in the curve at 1918-20 (maybe) and 1942-4 (definitely). The WWII "extinction event" continues through the 1945-7 interval. The slope of the curve per se doesn't seem to change that much, although the pre-WWII data are too rough to really tell. Third, the curve flattens out starting in 1984-86. Notes: 1) By running an RMA regression on the "clean" 1945-47/1981-83 intervals, I got a rate of growth in the literature of 7.8%/per year (r2 = 0.943; doubling time = 9.2 years). It doesn't help much to use the somewhat smoother 1963-65/1981-83 data; the rate goes down only to 7.2% (r2 = 0.930; doubling = 10.0 years), which is basically the same thing. 7% a year is fast! 2) The offsets are clearly related to the two world wars. The Great Depression didn't seem to make a big deal, which may say something about the financial resources of people like Osborn, Frick, and Carnegie (do any of you guys remember the old Carnegie Institution series?). Probably most of you are already familiar with the "WWII effect" on the literature, but the WWI effect was a surprise to me (assuming it's real). 3) There is _definitely_ a flattening in the curve, and I do not think it's merely due to my not keeping up with recent literature. The data start to go flat in 1984-86, which is a decade ago, and it should take far less than ten years for obscure North American references to land on my desk. Furthermore, the rate of growth doesn't merely slow - there's _no_ growth after this point. If you project the 7.2% growth rate from 1981-83's 158 references, there should be 363 references in 1993-96. The data are completely incompatible with a rate of growth that fast. I'm fairly confident about concluding from these data that the field (or at least the mammal paleo sub-sub-field) has reached the limits of its growth, and started doing so in the early 1980's. Has the ghost of Ronald Reagan come back to haunt us? Comments, anyone? Year References 1900 1 1903 3 1906 2 1909 4 1912 10 1915 12 1918 5 1921 6 1924 8 1927 9 1930 18 1933 24 1936 19 1939 33 1942 19 1945 9 1948 19 1951 16 1954 33 1957 26 1960 54 1963 40 1966 72 1969 78 1972 94 1975 110 1978 128 1981 158 1984 154 1987 149 1990 156 1993 67
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