The novel H3N2 strain first emerged in Hong Kong and spread worldwide, causing the Hong Kong flu pandemic, which resulted in 500,000–2,000,000 deaths. This was the first pandemic to spread significantly by air travel. H2N2 and H3N2 co-circulated after the pandemic until 1971 when H2N2 waned in prevalence and was completely replaced by H3N2. In 1977, H1N1 reemerged in humans, possibly after it was released from a freezer in a laboratory accident, and caused a pseudo-pandemic. Whether the 1977 "pandemic" deserves to be included in the natural history of flu pandemics is debatable. This H1N1 strain was antigenically similar to the H1N1 strains that circulated prior to 1957. Since 1977, both H1N1 and H3N2 have circulated in humans as part of seasonal influenza. In 1980, the current classification system used to subtype influenza viruses was introduced. At some point, IBV diverged into two lineages, named the B/Victoria-like and B/Yamagata-like lineages, both of which have been circulating in humans since 1983. In 1996, HPAI H5N1 was detected in Guangdong, China and a year later emerged in poultry in Hong Kong, gradually spreading worldwide from there. A small H5N1 outbreak in humans in Hong Kong occurred then, and sporadic human cases have occurred since 1997, carrying a high case fatality rate. The most recent flu pandemic was the 2009 swine flu pandemic, which originated in Mexico and resulted in hundreds of thousands of deaths. It was caused by a novel H1N1 strain that was a reassortment of human, swine, and avian influenza viruses.
Hostility  is seen as form of emotionally charged aggressive behavior. In everyday speech it is more commonly used as a synonym for anger and aggression. It appears in several psychological theories. For instance it is a facet of neuroticism in the NEO PI, and forms part of personal construct psychology, developed by George Kelly. Hostility/hospitality
For hunter gatherers, every stranger from outside the small tribal group was a potential source of hostility. Similarly, in archaic Greece, every community was in a state of hostility, latent or overt, with every other community - something only gradually tempered by the rights and duties of hospitality.Tensions between the two poles of hostility and hospitality remain a potent force in the 21st century world. Us/them
Robert Sapolsky argues that the tendency to form in-groups and out-groups of Us and Them, and to direct hostility at the latter, is inherent in humans. He also explores the possibility raised by Samuel Bowles that intra-group hostility is reduced when greater hostility is directed at Thems, something exploited by insecure leaders when they mobilise external conflicts so as to reduce in-group hostility towards themselves. Non-verbal indicators
Automatic mental functioning suggests that among universal human indicators of hostility are the grinding or gnashing of teeth, the clenching and shaking of fists, and grimacing. Desmond Morris would add stamping and thumping.The Haka represents a ritualised set of such non-verbal signs of hostility.