The mammal limb-- "prototype"

Where did mammal limbs come from? Recently it is argued that primitive fish, over 300 million years ago, had five digit fins.

(The pectoral fin of Panderichthys and the origin of digits. Catherine A. Boisvert, Elga Mark-Kurik & Per E. Ahlberg Nature advance online publication 21 September 2008 doi:10.1038/nature07339)

Evolution of forelimbs-- fetal similarities become specialized. Primates retain the fetal form, more or less, modified by by the HACNS1 gene and perhaps others. Even the earliest known primate has five digits, with a nail on each.

 

A transition claw-nail has recently been discussed (2012), a 47 mya fossil with a lemur-like grooming claw on its second digit (image).

From the earliest writings on human evolution, hands were recognized as a fundamental developent in the evolution of humans. See Engels (1876) in his "...transition from ape to man" where he argued that using hands for more than locomotion and becoming bipedal was "the decisive step from ape to man." (Engels goes on to consider the virtues of labor.. the hand is not only the organ of labor but "it is also the product of labour." (This essay is of interest also for its brief discussion of language origins and ecology.

evolution of the primate hand -more on hands here. And here, 2010 report.

The grasping hand of primates and especially apes. Compare with their feet and feet bones.

The evolution of the human hand

"Our results evoke the hypothesis that human-specific adaptive evolution in HACSN1 has contributed to uniquely human aspects of digit and limb patterning. The dexterity of the human hand is due to morphological differences compared with other primates that include rotation of the thumb toward the palm and an increase in the length of the thumb relative to the other digits. Human-specific changes in hindlimb morphology, such as the characteristic inflexibility and shortened digits of the human foot, facilitated habitual bipedalism..."

Prabhakar, S., Visel, A., & al. (2008). Human-specific gain of function in a developmental enhancer. Science, 321, 1346-1350.

 

Neanderthal grip doesn't seem much different from humans.

The human pinky plays a significant role in the efficiency of the human hand in tool use. (See Alda SA video clip.) Alda also has a video bit on the speculative significance of the human foot in evolving larger brains via running.

But what about animals that do not have five digits-- snakes or birds for example?

Prmate locomotion-- four types

Muybridge's running baboon photos (also see them wading on Youtube!)

early and late bipedal ape skeletons The efficient human foot may be only 1.8 million years old.

(Vereecke, E. E. and Aerts, P. (2008). The mechanics of the gibbon foot and its potential for elastic energy storage during bipedalism. J. Exp. Biol. 211, 3661-3670. )

References and summary on walking --we are not from knuckle walkers. What is the relation between hand and foot evolution. ?