Pregnancy websites have some handy hints for mothers-to-be about how they could use their placenta in making prints, using the placenta to make patterns on paper.
Lighter-coloured pixels denote less pen pressure on the paper, so differences between samples indicate different patterns of pen pressure and thus the likelihood that different authors were involved.
If you simply update the approach used in Mr Krugman's 1995 paper to take into account today's trade patterns, you find that the effect on wages has increased.
In the PNAS paper, the researchers said that socio-economic indicators from 1900 provided a better explanation of current patterns of invasive species than indicators from 2000.