Addicted to Adduction

The inability of creationists to deal honestly with scientific evidence is legendary, especially when it comes to human evolution. Answers in Genesis and the Institute for Creation Science are the standard bearers of disingenuity.

Jim Foley has a post up at the Panda's Thumb about the latest creationist effort, this time concerning the recent find of 1.5 million year old fossil footprints from Illeret, Keyna.

One thing caught my attention was a neat story concerning the hallux, or big toe.

Discussing the different characteristics of modern, Illeret and Laetoli footprints (and hence exposing the claims by creationists that they are all the same, and so human), Jim mentions the hallux and abduction. Abduction of the hallux can be explained as the 'movement' of the hallux away from the line of the foot.

Compare your left hand and foot. Draw an imaginary line through the length of the foot. The hallux is set slightly off that line (taking in to account changes to the big toe caused by a lifetime of wearing shoes). Now, compare that the your left hand. The thumb is at a much greater angle to a line along the length of the hand. The thumb is abducted to a much greater extent that the hallux.

The foot of our distant ancestors would have had been more like our hand in terms of the position of the hallux - for prehensile reasons. But as our ancestors moved to be primarily ground dwellers and upright bipedalists, the shape of the foot evolved. The big toe adducted (moved closer the the line of the foot - the opposite of abducted) and the footprints at Illeret and Laetoli show this rather neatly.

The angle of abduction in modern humans is around 8 degrees (see figure showing abduction angle for the left foot). The angle of abduction of the Laetoli prints (at 3.7 mya) is 27 degrees. The angle of abduction for the Illeret prints (at 1.5 mya) falls neatly in between these two values at 14 degrees.

Now, what is another name for something that falls somewhere between two conditions? . . . Umm . . . Oh yeah, . . . intermediary.