Today's herds of milu, also known as Pere David's deer, are descended from animals that, for more than 1,000 years, were fed and protected as imperial pets. Still, they respond fearfully to the sounds and images of their ancestral predator, the tiger, mainland scientists have found. The scientists, from the Chinese Academy of Sciences' Institute of Zoology, had set out to settle one of the hottest debates in animal behavioural science - whether a species can pass its collective memory from one generation to the next. They turned to milu for an answer. 'Animal behaviour is the result of genetic and acquired learning,' said Professor Li Chunwang , one of the researchers. 'Animal behaviour passed down from generations is produced by genetic factors and offspring inheriting their parents' behaviour through learning.' The mainland team built on studies around the world that had examined other animals, including guinea pigs, America's oldfield mice and Australia's tammar wallabies, but had obtained mixed results. The researchers believed milu could provide more reliable evidence because this type of deer is one of the few large mammals to have gone extinct in the wild but remain well preserved in captivity. They wanted to know how milu reacted to the presence of various animals, such as tigers, lions, wolves, dogs and crows. In the two biggest milu parks on the mainland, the Dafeng Pere David's Deer Nature Reserve and the Beijing Milu Park, they played soundtracks of those animals and showed the milu their photos using devices hidden in bushes. The milu reacted differently to the perceived presence of tigers than to all other animals. They stared, approached and then fled from the sounds and images of tigers, typical reactions to the detection of a predator. In contrast, the roar of a lion, a predator unknown to native animals in China, attracted the deer's attention but did not cause them to flee. Li said the milu's memory of their ancestral predator led zoologists into an unknown world. 'Human learning is easy to understand, but in the case of animals, how could learning take place in the absence of predators for generations? This is probably not a simple problem. It is a direction for future research.' The team's peer-reviewed paper was published in August by Plos One, an open-access journal of the Public Library of Science in the US.