I love the explaination the society gives in the Insight book that Apognophos posted.
*** it-1 pp. 164-165 Ark ***
The “kinds” of animals selected had reference to the clear-cut and unalterable boundaries or limits set by the Creator, within which boundaries creatures are capable of breeding “according to their kinds.” It has been estimated by some that the hundreds of thousands of species of animals today could be reduced to a comparatively few family “kinds”—the horse kind and the cow kind, to mention but two. The breeding boundaries according to “kind” established by Jehovah were not and could not be crossed. With this in mind some investigators have said that, had there been as few as 43 “kinds” of mammals, 74 “kinds” of birds, and 10 “kinds” of reptiles in the ark, they could have produced the variety of species known today. Others have been more liberal in estimating that 72 “kinds” of quadrupeds and less than 200 bird “kinds” were all that were required. That the great variety of animal life known today could have come from inbreeding within so few “kinds” following the Flood is proved by the endless variety of humankind—short, tall, fat, thin, with countless variations in the color of hair, eyes, and skin—all of whom sprang from the one family of Noah.
As many have mentioned in the past, who are these investigators? I have written to the society asking for that info and had no reply...I can find no proof on the internet to back this claim up from any scientist or report, the only mentions I get are from creationist websites...which ain't proof!