请教：GWD-7 Q6-9的一段话的意思~~~

For many years, theoretical

       economists characterized humans

       as rational beings relentlessly bent

Line       on maximizing purely selfish reward.

  (5)      Results of an experimental economics

study appear to contradict this view,

however.  In the “Ultimatum Game,”

two subjects, who cannot exchange

information, are placed in separate

 (10)      rooms.  One is randomly chosen to

propose how a sum of money, known

to both, should be shared between

them; only one offer, which must

be accepted or rejected without

 (15)      negotiation, is allowed.

      If, in fact, people are selfish and

rational, then the proposer should offer

the smallest possible share, while the

responder should accept any offer,

 (20)      no matter how small:  after all, even

       one dollar is better than nothing.  In

       numerous trials, however, two-thirds

of the offers made were between

40 and 50 percent; only 4 percent

 (25)      were less than 20 percent.  Among

responders, more than half who were

offered less than 20 percent rejected

the offer.  Behavior in the game did not

appreciably depend on the players’

 (30)      sex, age, or education.  Nor did the

amount of money involved play a

significant role:  for instance, in trials

       of the game that were conducted in

Indonesia, the sum to be shared was

 (35)
                    as much as three times the subjects’

average monthly income, and still

responders refused offers that they

deemed too small.

上面高亮部分是什么意思？为什么这个实验中如果人性自私的话the responder should accept any offer, no matter how small？