Tuesday, February 14, 2017

The evolution of women's clothing sizes

Several years ago I presented a piece about the Evolutionary history of Mazda motor cars, in which I pointed out that what is known in biology as Cope's Rule of phyletic size increase applies to manufactured objects as well as to biological organisms. This "rule" suggests that the size of the organisms within a species generally increases through evolutionary time. Human beings, for example, are on average larger now than they were a few thousand years ago. Furthermore, through time, new species arise to occupy the niches that have been vacated (because the previous organisms are now too big to fit).

This situation is easy to demonstrate for cars, because all successful car models get bigger through time — the customers indicate that the car is not quite big enough, and the manufacturer responds. Another simple example is women's clothing, which I will discuss here.

Women's clothing changes through time in response to two factors in the modern world: changes in the "desired" image of women (as discussed in the post on Changes in Playboy's women through 60 years), and increasing obesity in western society (see the post on Fast food and diet). Illustrating Cope's Rule in this case is thus easy.

There have been five voluntary "standards" developed over the past century for standardized clothing sizes in the USA, as discussed in Wikipedia. These standards describe, for example, what sized woman should fit into a Size 12 in terms of various of her dimensions. There is nothing mandatory about these standards, and they simply reflect societal recommendations at any given time. So, a Size 12 in 1958 is not the same as a Size 12 in 2008.

These three graphs illustrate the time course of the changes in each of the defined clothing sizes (Size 0 to Size 20), in terms of three female girth measurements.

This is blatantly Cope's Rule in all three cases. All of the sizes get bigger through time, at approximately the same rate. Furthermore, as the dimensions increase through time, new sizes appear to fit the smaller women — Size 8 did not exist in 1931, Size 6 did not exist in 1958, Sizes 2 and 4 did not exits in 1971, and sizes 0 and 00 did not exist in 1995.

To put it another way, a Size 12 woman today is much larger than her Size 12 mother was, who in turn was bigger than the Size 12 grandmother. I believe that this is referred to in the clothing business as "vanity sizing", which it may well be, but it is also a natural example of Cope's Rule of phyletic size increase.

Finally, there is no reason to expect that this phyletic size increase will stop any time soon. Do cars or clothes have an upper limit on their size? Biological organisms do, mainly because of the effect of gravity, and so the phyletic size increase either ceases or the species becomes extinct. Manufactured objects are different.

Data sources
  • DuBarry / Woolworth (1931-1955) - see Wikipedia
  • National Institute of Standards and Appeals (1958) Commercial Standard CS215-58: Body Measurements for the Sizing of Women's Patterns and Apparel Table 4
  • National Institute of Standards and Appeals (1971) Commercial Standard PS42-70: Body Measurements for the Sizing of Women's Patterns and Apparel Table 4
  • ASTM International (1995, revised 2001) Standard D5585 95 (R2001)
  • ASTM International (2011) Active Standard D5585 11e1: Standard Tables of Body Measurements for Adult Female Misses Figure Type, Size Range 00–20

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