1 . “Flying insects don’t fly directly to lights from far away because they’re attracted to them, but appear to change course toward a light if they happen to be passing by due to a strange inborn biological response,” writes Samuel Fabian, a bioengineer, in a research paper.

Until now, the leading scientific hypothesis has been that insects use the moon’s light to direct the way at night and mistake artificial lights for the moon. But this idea doesn’t explain why insects that only fly during the day also gather around lights.

To find out what really happens, Samuel’s team track the precise movements of insects in the wild around lights using a high-speed camera. This revealed two notable behaviours. First, when insects fly above lights, they often invert (转向) themselves and try to fly upside down, causing them to fall very fast. Just after insects pass under a light, they start doing a ring road. As their climb angle becomes too steep, they suddenly stop and start to fall. Second, when insects approach a light from the side, they may circle or “orbit” the light.

The videos show that the inversions sometimes result in insects falling on lights. It can appear to the naked eye as though they are flying at the lights. “Instead, insects turn their dorsum toward the light, generating flight perpendicular(垂直) to the source,” the team write. It is common to the two behaviours that the insects are keeping their backs to the light, known as the dorsal light response (DLR). This DLR is a shortcut for insects to work out which way is up and keep their bodies upright, as the moon or sun is usually more or less directly above them, and this direction allows them to maintain proper flight attitude and control. They also find that the insects fly at right angles to a light source, leading to orbiting and unstable flights as the light’s location relative to them changes as they move.

Samuel’s team suggest that a possible outcome of the research could help the construction industry to avoid the types of light that most attract insects.

2 . Many people would answer the question of what makes us human by insisting that we are cultural beings. There is no doubt that we are. But one definition of culture is the totality of traditions acquired in a community by social learning from other individuals, and many animal species have traditions. Can we then say that some animals are cultural beings too?

One approach to study culture in animals is the so-called Method of Exclusion (排除), in which scientists investigate behavioral variations across populations of one species. In a famous study, scientists learned that chimpanzee (黑猩猩) behaviors were socially passed on as they were present at some sites but not at others, despite having same ecological settings. For example, chimpanzees in Tai National Park in Ivory Coast are well-known for their nut-cracking skills. Chimpanzees in Gombe national part in Tanzania, on the other hand, do not crack nuts, although nuts exist in their environment too.

However, when applying the Method of Exclusion, one has to be very careful. There are other factors that could also explain the pattern of behavioral evaluation. For example, some of the chimpanzee techniques scientists evaluated occur in only one of the three subspecies. So it’s quite possible that these behaviors also have an innate component. This would mean that one chimpanzee subspecies uses a new technique not out of cultural tradition, but because the behavior is fixed to specific genes. Another factor that has to be excluded is of course the environment Chimpanzees in Mahale do not fish algae (水藻), simply because algae does not exist there.

But when we exclude all the variations that can be explained by genes or environment, we still find that animals do show cultural variations. Does that mean there is no real difference between them and us after all? Not exactly: There is a fundamental difference between human and animal culture. Only humans can build culturally on what generations before us have learned. This is called “cumulative culture”. We don’t have to keep reinventing the wheel. This is called the “ratchet (棘轮) effect”. Like a ratchet that can be turned forward but not back, people’s cultural techniques evolve.

It is likely that behaviors we see today in chimpanzee cultures could be invented over and over again by individual animals themselves. In contrast, a child born today would not be able to invent a computer without the knowledge of many past generations.