228 // Universal Letter of Reference
for haemoglobin to evolve. However, for much of that time, it wouldn’t have had any useful function – complex creatures able to survive in a toxic oxygen atmosphere did not arrive until 1.5 billion years or so had passed, and blood cells arose a lot later than that – and it turned up fairly rapidly, by geological standards, once the scene was set for it to do something useful. But it did so through a sequence of processes that combined small molecules into bigger ones, then those into bigger ones still. It didn’t just faff around at random hoping to hit the haemoglobin jackpot by choosing the right 1,700 DNA letters.
........................................... Universal Letter of Reference Dear Search Committee Chair, I am writing this letter for Mr XXXXX, who has applied for a position in your department. I should start by saying that I cannot recommend him too highly. In fact, there is no other student with whom I can adequately compare him, and I am sure that the amount of mathematics he knows will surprise you. His dissertation is the sort of work you don’t expect to see these days. It definitely demonstrates his complete capabilities. In closing, let me say that you will be fortunate if you can get him to work for you. Sincerely, A. D. Visor (Prof.) From Focus Newsletter, Mathematical Association of America.
........................................... Snakes and Adders This is a playable game for two or more players with topological and combinatorial features. It is a slight modification of a game that Larry Black invented in 1960, called the Black Path Game.