During the late 1990s people used to talk about the "post-80s" generation – those people born in the 1980s. Now the post-90s generation has arrived and is approaching the age of 20 – ready for college enrollment or the job market.

The rise of both generations is inevitable. When we talked about these groups of youth a decade ago, they were almost children. Now these youth are becoming the labor force – a sign of a fundamental change of the Chinese society.

People often refer to the post-80s generation as the "Bird's Nest Generation," drawing on the nickname for the landmark National Stadium, the most emblematic venue of the 2008 Beijing Olympic Games. One of the features of this world event in China was the young Chinese volunteers, mostly belonging to the post-80s generation, who showed their openness, confidence and spirit of service to the whole world. These young people can speak foreign languages; they open their arms to people of different countries and races; and they are respectful and tolerant of both Western culture and Chinese traditions. They have injected new blood into the "China Dream."

The Shanghai World Expo is witnessing more and more post-90s volunteers, who are dubbed the "Haibao Generation," drawing on the name of the mascot for the Shanghai Expo. The "Haibao Generation" has grown up in an era that has seen China's rapid rise amid huge economic progress.

The change in China's environment and social conditions give these young people three main features: They are more aware of their individual feelings, more focused on consumption and have a wider world vision. They do have their own weaknesses as well: They are more fragile, more sensitive and less resistant.

The younger generation is always a hot social topic. After the Wenchuan earthquake in 2008, many post-80s young Chinese ventured to the quake zone from across the country to help victims, demonstrating their volunteer spirit and enthusiasm for public affairs; this won them the respect of China and the world. Later that year their smiles, as volunteers for the Beijing Olympic Games, again gave the world a positive impression. This young generation of Chinese is helping the world understand China better.

The even younger post-90s volunteers serving at the Shanghai World Expo have carried on the spirit of the "Bird's Nest Generation." I've seen for myself at the Expo Park their perseverance and enthusiasm. Their spirit of optimism and their committed service have again assured a clearer "China Dream." Both of these young Chinese generations are showing how China has grown and display different aspects of the "China Dream."

Zhang Yiwu is a professor of Chinese and Deputy Director of the Center for Cultural Resources at Peking University.