A season on the island: garter snakes hunt salamanders, and hawks hunt snakes. You are the snake outlined in red; steer with the mouse. A season opens over the page; at winter you come back to the pedigree.
The hawks come early in the season and take every snake above ten: a hawk's shadow falls where its snake is heading, so get out of it. Then 30 salamanders come out over the season, and a young snake costs 2. A snake that eats nothing dies before winter. At winter the fed snakes pair at random, yours too; each pair has as many young as their salamanders pay for.
Every snake carries one chromosome from each parent, with seven genes on it. In the pedigree each chromosome is a string of seven beads; every gene starts plain grey.
Your first snake carries one new allele, a colour. After that, one new allele turns up each generation, in a young snake at random, at a gene at random. A ring marks the bead where each one arose. None of them does anything.
Next season you play one of your young.
Pedigree, below: every snake that has lived, one row a generation, mother's chromosome above, father's below. Your snakes glow red; the snakes you descend from, or that descend from you, glow pale red.
Point at a bead, one gene on one chromosome, and lines show where that copy came from (red, up) and where it went (blue, down). Click a bead to keep its lines.