Heavy Breeding. "In 1920, the brothers Lutz and Heinz Heck, directors of the Berlin and Munich zoos, respectively, began a two-decade breeding experiment. Working with domestic cattle sought out for their 'primitive' characteristics, they attempted to recreate 'in appearance and behavior' the living likeness of the animals’ extinct wild ancestor: the aurochs. 'Once found everywhere in Germany,' according to Lutz Heck, by the end of the Middle Ages the aurochs had largely succumbed to climate change, overhunting, and competition from domestic breeds."