Changes from the outside

為何這些動詞(紅字的部份)用過去式?
但第二段那個"agree"卻又用現在式?

In the late 1920s, researchers found a tribe of untouched by modern society. This was the first reported meeting with the Yanomami, who were living deep within the South American jungle.

Scientists agree that their location deep in the forest helped keep their culture unchanged. Until recently, most  Yanomami still lived in isolated regions. Everything they needed came from the rain forest. They hunted, fished and farmed the land. Then a discovery brought the outside world to them. And along with it came deadly changes.




[StudioClassRoom 11 2012]