... genera evolved in the tropics, they expanded towards the poles. In time,however, the bivalves near the poles became extinct while their cousins near the equator survived. From these results, Jablonski ... oxygen opened the door for animal evolution, what pushed the ani-mals through? Part of that answer may lie within the animals themselves—inparticular, in the set of genes that control their development. ... swim through the water or burrow into the muck. Withtheir guts, they could swallow larger microbes, and, eventually, could even startto attack other animals. Figure 10.12 shows a 550-million-year-old...