June 27, 2007

A colorless world

Every so often I'm baffled by a graph, table, or other illustration in the New York Times: I can't figure out what the scales are, what the numbers represent, etc.  Yesterday I was stumped by an elaborate illustration concerning "genetic differentiation in modern humans", accompanying Nicholas Wade's "Humans Have Spread Globally, and Evolved Locally" in the Science Times of 6/26/07, p. 3.  This is a map of the world with icons (outline forms of human beings) on it representing 52 modern human populations, each icon coded for the makeup of the average genome for that population, with respect to five "modern genetic clusters" (Africa, Eurasia, East Asia, Oceania, America).  The coding assigns a different shading for each cluster, but I was able to pick out only one shading (for East Asian) as distinguishable from the other four (by being noticeably darker).  The illustration was almost completely uninterpretable.

Then I realized what must have happened, and this morning I verified my hypothesis.

The clue was a note pointing to a line on the map: "Blue lines show ancestral human migrations, which formed the basis for modern populations."  There are indeed lines on the map, with arrowheads suggesting the direction of migrations.  But there are no BLUE lines; the entire illustration is in grayscale.  Ah, I thought, this illustration was supposed to be in color.

On the Times website, it is.  African is yellow, Eurasian is blue, East Asian is red (and darker than the other colors), Oceanian is green, and American is purple, or at least a purplish blue.  Some of the icons have several colors, representing the makeup of the population in question.  There's a lot of information in that illustration, but much of it depends on the colors.

Clearly, the illustration was meant to be in color, and there are a number of other colored illustrations in this Science Times, but somehow this one escaped reproduction in color.  Well, things go wrong.

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Posted by Arnold Zwicky at June 27, 2007 10:43 AM