Have you noticed the phenomenon of puppy dog eyes, the inner eyebrow raising movement of dogs? Do you believe it a result of \_41\_ for dogs to appeal to humans? Researchers dissected dog and wolf heads and found that the facial muscle anatomy of both animals was almost identical -- \_42\_ an eyebrow muscle, found only in dogs. The inner eyebrow raising movement makes the dogs' eyes appear larger and more infant like, \_43\_ prompts a "nurturing" response in humans. When dogs make the movement, it seems to elicit a strong desire in humans to \_44\_ them. This would give the dogs that moved their eyebrows more a selection advantage over others, reinforcing the trait in \_45\_ generations. The findings show how important faces can be in capturing our attention, and how powerful facial expression can be in social interaction. Hikikomori is a psychological condition which makes people shut themselves off from society, often staying in their houses for months on end. There are at least half a million of them in Japan. It was once thought of as a young person's condition, but sufferers are getting older and staying locked away for longer. It is an economic as well as a social threat to the country, and is seriously worrying Japanese government. As of 2015, there were 541,000 hikikomori aged 15-39 in Japan, according to government statistics. There is no data on other age groups, suggesting that the figure is likely to be far larger. Some families are also loath to report hikikomori in their households, Kingston said. Doctors began to observe hikikomori as a social phenomenon around the mid-1980s, when young men exhibited signs of lethargy, refused to communicate, and spent most of their time in their rooms. There's no unifying reason why people become hikikomori. Some withdraw from society because they feel they don't know what to do with their lives and can no longer cope with the pressure from people around them. Others are triggered by events in their lives, like bad grades or heartbreak. Hikikomori feel a deep sense of shame that they cannot work at a job like ordinary people. They think of themselves as worthless and unqualified for happiness. Almost all feel remorse at having betrayed their parents' expectations.