A look at academic family trees branches out to consider whether chemists need to take a leaf out of mathematicians' book of numbers.

Academic lineages — tracing your 'family tree' back through your supervisor's supervisor's supervisor's supervisor's... (you get the picture) — were raised by Jeremy on the ChemBlog (http://go.nature.com/HmZNsB) and carried on by Sam on Everyday Scientist (http://go.nature.com/NdhxoH). Jeremy has traced his “as far back as Breslow”, but Sam goes a good few steps further. Climbing his PhD supervisor's tree, he passes Helmhotz and Leibniz's father on as far as Gerard van Swieten (1700–1772). Using the roots of his postdoc adviser he gets to Justus von Liebig and then even further, to Niccolò Leoniceno in the fifteenth century. For those interested in researching their own trees, the ChemBlog suggests several chemistry departments that have resources, including the University of Texas at Austin (http://go.nature.com/DwoEXJ) and the University of Illinois at Urbana–Champaign (http://go.nature.com/ri4DSe).

Some of the comments on the Everyday Scientist post alert readers to the concept of the Erdős number (http://www.oakland.edu/enp) in mathematics. If someone co-wrote a paper with prolific mathematician Paul Erdős, they are given an Erdős number of 1. Those who have co-written a paper with such individuals have an Erdős number of 2, and so on. Is there a chemist who has been prolific enough in a range of disciplines to be a useful measure in our own fair subject? Discussion raged in our office, with suggestions including Pauling, Woodward, Cotton, Grubbs, Whitesides and so on — all of whom are identifiable without a first name! Unfortunately, we can't think of any single chemistry candidate who quite fits the bill. Maybe each sub-discipline needs its own champion, and we should pick a recent Nobel Laureate in each area. So physical chemists could have an Ertl number, inorganic chemists a Schrock number and organic chemists a Sharpless number. Get on to Web of Science and start calculating your numbers!