BIPEDALISM MODEL EVALUATOR		Home
Classification: Forelimb pre-emption (carrying models) Mnemonic: "Freeing of the hands"
Specific Model:	Female-driven infant carrying
Original Proponent(s):	Etkins (1954); Tanner (1981)
Assessment:	Popularity Ranking: 1st out of 9 categories (86% of texts) Simple Evaluation: #37 /42 (45%) Detailed Evaluation: #30 (=2) /42 (50%)
Basic Summary:	Infant carrying, predominently by females, was the key driver of human bipedalism.
Discussion:	Etkins (1954:136) discusses the potential social behaviour of early hominids, assuming that they had a division of labour along the lines of ‘man the hunter’ ‘woman the gatherer’. Like Lovejoy, he assumes that pair bonding would have been the natural result of such scenarios. “The central feature of the social behaviour of the ‘hunter’ anthropoid therefore, must be an integration of the male into the monogamous family unit in which he is the primary hunter.” Etkin (1953:137) Tanner (1981), also argued that sexual selection would have favoured “males who sometimes shared food” (p164) but, unlike Lovejoy, added that female bipedality would also have been strongly selected for, both for gathering plants and carrying infants.
Strengths:	A scenario for human bipedalism that also helps explain increased altriciality and pair bonding.
Weaknesses:	Rather teleological. Just because mothers carry their babies bipedally today does not help explain how bipedalism originated.
Evaluation:
1.1 Survival Value	6 (Fair) In as much as carrying infants bipedally confers greater survivability on them this model does provide some potential survival value.
1.2 Sexual Selection	7 (Good) This model was rated fairly high on the assuming that female infant carrying ability could have provided a means for male sexual selection.
1.3 Not Teleological	2 (Poor) Bipedal female carrying of infants is clearly a modern human phenomenon but there is no strong argument here as to why is could have been the major factor leading to our bipedality.
2.1 Improved Food Acquisition	6  (Fair) This model is fairly neutral in terms of this criterion.
2.2 Accounts for Predation	0  (Poor) Whatever threat of predation might exist for an early hominin can only be drammatically increased whilst carrying a helpless infant.
2.3 Why Apes are not Bipedal	3 (Poor) Etkins and Tanner do not offer any good arguments as to why increased carrying of infants increased in our lineage but not in other apes.
2.4 Extant Analogues	6 (Fair) Although there is evidence that chimpanzees and bonobos ocassionally carry infants bipedally, more often they carry them quadrupedally.
2.5 Applies to Both Sexes	2  (Poor) This is a very assymetrical model in terms of the role of the sexes.
3.1 Hominid Anomalies	5  (Fair) This was judged a neutral model on this criterion.
3.2 Fits Paleoecological Record	5  (Fair) This was judged a neutral model on this criterion.
3.3 Precursor to Strider and knuckle Walker	4  (Fair) This was judged a neutral model on this criterion.
4.1 Extended Explanatory Power	7  (Good) As with Lovejoy's Provisioning model, this, simpler, infant carrying idea also helps to explain increased altriciality and monogamy.
4.2 Complimentary	5  (Fair) This model was judged to be compliementary to most other carrying models except those promoting the carrying of weapons and for threat displays. For those it was judged 'compatible'. Like other carrying models it was largely judged contradictory to climbing models.
4.3 Falsifiable or Testable	0  (Poor) This idea was very much open speculation. It was not put in a rigorous scientific way open to any attempt at verification for example by making predictions.
References	Etkin, William (1954). Social Behaviour and the Evolution of Man's Mental Faculties. American Naturalist Vol:88 Pages:129-142 Tanner, Nancy Makepeace (1981). On Becoming Human. Cambridge University Press (Cambridge)