HONG KONG: Sun Zhengcai earned his PhD from China Agricultural University in 1997, experimenting with different fertilizers for crop rotation in northern China, according to his doctoral thesis.

For the world's biggest grain grower and consumer, this type of research is crucial for improving yields. But it was an unlikely qualification for political leadership in China where engineers have traditionally held many of the top posts.

Sun represents one of the more far reaching changes in Chinese politics. Highly educated leaders in a broad range of disciplines are rising to the top of the ruling Communist Party, according to data from Connected China, a Reuters database application that tracks the connections and careers of China's leaders.

Sun, 49, who joined the Politburo at November's Communist Party Congress, is one of five PhD holders in a body in which all 25 members have at least a junior college education.

Some education experts explain the rise of this more highly educated leadership class as a product of the increasing complexity of China's economy and society.

It also reflects an evolution in the Party. A generation of revolutionary soldiers gave way to technocratic engineers who guided the following period of industrialization. The engineers are now handing over to leaders better qualified to run the world's second-biggest economy.

"As the society matures, it is always beneficial to have a leadership with diverse backgrounds," said Gong Peng, a Professor at Tsinghua University's Centre for Earth System Science. "They bring different thinking and skills to the administration."

The data from Connected China shows far more Politburo members now hold PhDs and graduate degrees than earlier leadership generations.

It also shows that education is not necessarily the only path to power: loyalties forged during political posts in the provinces, and family ties to former leaders also matter a great deal.

DR XI AND DR LI

The other PhD holders in the current Politburo are party leader and incoming President Xi Jinping, who studied China's rural markets at Tsinghua University. Li Keqiang, expected to become Premier after the National People's Congress in March, has a PhD in economics from Peking University. Liu Yandong studied China's political development at Jilin University, and fellow Politburo member Li Yuanchao explored socialist art and culture in his thesis at the Central Party School.

The current Politburo also features nine members with masters degrees and three with other higher degrees. That stands in stark contrast with members of the 14th Politburo formed in 1992. Only Hu Jintao and Wen Jiabao, who became China's top leadership duo a decade later, had graduate degrees in that group.

The change in the breadth of education has also been dramatic. Ten years ago, 15 of the 20 college-educated members of the Politburo were trained in engineering or the physical sciences. At the very top of China's hierarchy, engineers were even more heavily represented.

In the nine-member Politburo Standing Committee appointed in 2002, eight members of the party's top decision-making body were engineers and one was a geologist. Of these, four were engineering graduates of Tsinghua.

The current Politburo has only four engineers. They are outnumbered by colleagues with training in economics, finance and business management. It also shows a sharp increase in members educated in law, humanities and social sciences. The seven-member Standing Committee has only two engineers; Xi Jinping, who has an undergraduate degree in chemical engineering and Yu Zhengsheng who worked in missile guidance.

For some Chinese educators, the presence of fewer engineers at the top is a welcome development after decades in which technocratic leaders, often Soviet trained, dominated decision-making in Beijing.

"Engineers who do not learn about management may not be good managers and eventually good administrators," says Tsinghua's Gong. "I think it will improve the governing quality in China."

WORLDY LEADERS

In the early 1980s, then paramount leader Deng Xiaoping directed the party to foster a generation of better educated cadres who could accelerate China's market reforms.

China's subsequent rise as a major trading nation and growing military power is also increasing pressure on the party to select better educated and more worldly leaders, political analysts and education experts say.

"Because the country is changing and the world is changing, it requires a more sophisticated understanding of the issues," says Yu Maochun, an expert on Chinese politics and a professor at the Annapolis, Maryland-based United States Naval Academy.

Some experts question whether academic qualifications are as important as loyalty and family ties in a political system where many senior leaders, including Xi Jinping, are "princelings", children of senior party veterans.

EXPERIENCE IN PROVINCES

Data from Connected China shows an increasing emphasis on provincial-level party leadership experience for Politburo members.

In 1992, only nine of 23 Politburo members served as a provincial or municipal-level party chief. In the current Politburo, 19 of the 25 have held or currently hold a provincial post at this level, including Sun Zhengcai who is party secretary in Chongqing.

Many of the engineers who held top posts, including President Hu Jintao, spent long periods working in unrelated fields.

"They are not really engineers in the Western sense," says Yu. "They are really political hacks. Their career paths were not devoted to science but concentrated on the political system."

Despite the increasing diversity of education at the upper levels of the party, one feature of China's leadership remains virtually unchanged since the revolutionary period - the domination of men.

Only two women are in the current Politburo, Liu Yandong and Sun Chunlan, and none are in the Politburo Standing Committee.