Two people collected the data, two did the analysis and wrote the paper, three helped a bit, one got the grant which funded the lab. Or something similar. The

Two people collected the data, two did the analysis and wrote the paper, three helped a bit, one got the grant which funded the lab. Or something similar. The incentives for giving credit to everyone who participated even a bit are quite strong: in most academic disciplines you get more than an eighth of a paper's worth of 'credit' for an eight-author paper.