Whether it is"women and children first"or"every man for himself"in a shipwreck may depend on how long it takes the ship to sink，researchers said recently．
When the Lusitania was torpedoed （用鱼雷袭击） by a German ship in 1915，it sank in 18 minutes and the majority of the survivors were young men and women who responded immediately to their powerful survival instincts．
But when the Titanic struck an iceberg in 1912，it took three hours to go down，allowing time for more civilized behavior to take control--and the majority of the survivors were women，children and people with young children．
Economist Benno Torgler of the Queensland University of Technology in Australia and his colleagues studied the two sinkings in order to explore the economic theory that people generally behave in a"rational"and selfish manner．The two tragedies provided a"natural experiment"for testing the idea，because the passengers on the two ships were quite similar in terms of gender and wealth．
The major difference was how long it took the ships to sink．They suggested that when people have little time to react，instincts may rule．When more time is available，social influences play a bigger role．But psychologists noted that many factors other than following social norms （社会规范）could come into play in a disaster，including an evolutionary urge to save the species，attachments that are formed between individuals during the event and the leadership of authority figures．
The extent of altruism（利他主义）and how it occurs"is a very controversial issue，"said Anthony R．Mawson，a professor of preventive medicine at the University of Mississippi Medical Center．He thinks the dominant response was attachment behavior．
Psychologist Daniel Kruger of the University of Michigan，US thinks that the answer lies less in social norms and more in our evolutionary heritage．Human beings have a deep instinct to preserve our kind，he said，and that means"people are more likely to save those who have higher reproductive value，namely the young and women in child-bearing years"．
Kruger also stressed the importance of leadership during a disaster，noting that the Titanic's captain appeared to have greater control than the Lusitania's．
（Note：Answer the questions or complete the statements in NO MORE THAN 12WORDS）

(1) According to Benno Torgler，what led to the different results between the two shipwrecks？
______

(2) Besides social norms and leadership，what other factors play a part in disaster behavior？
______

(3) According to Daniel Kruger，Why do the young and women of child-bearing age take the priority to survive？
______

(4) What does the passage mainly tell us？
______ ．