Classification: Efficiency
Mnemonic: Tree to Tree
Specific Model: Improved efficiency of moving from tree to tree
Original Proponent(s): Rose 1977; Pickford 1991    
Basic Summary: Shuffling bipedalism whilst moving from tree to tree was the precursor to human bipedality.    
Assessment: Popularity: The general efficient model classification was ranked 3rd most popular (out of 9) of the texts reviewed. 11% referred to this idea specifically.
Simple: #6 / 42 (66%)
Detailed: #6 (=2) / 42 (64%)
Discussion: Several paleoanthropologists, e.g. Rose (1977), Wrangham (1980), Hunt (1994) have suggested that movement between trees would have been more efficient if the hominin would have remained on two legs rather than getting down on all four and then returning to an upright posture again. This idea has most often been associated with feeding behaviour and a kind of "shuffling" bipedalism is suggested where the hominin remains upright during feedng bouts and then shuffles across from branch to branch and from tree to tree, rather than reverting to quadrupedalism. However, it can also be invoked simply when considering movement from tree to tree.

This idea overlaps heavily with Hunt's "Postural Feeding" hypothesis and the 'general gathering' idea, but is included here under the category of energy efficiency because arguments can be made form perspective alone without considering feeding.  
1.1 Survival Value 5 (Fair) This model was rated neutral by this criterion.    
1.2 Sexual Selection 5 (Fair) This model was rated neutral by this criterion.    
1.3 Not Teleological 9 (Good) As this model is based on extant ape behaviour it plausibly proposes a behaviour that couldhave ben practiced by early hominins without the need for modern human uses.    
2.1 Improved Food Acquisition 7 (Good) As the model places early homnins in relatively food rich forested settings it was judged 'good' by this criterion.    
2.2 Accounts for Predation 7 (Good) Close proximity to trees led this idea to be judged 'good'  by this criterion.    
2.3 Why Apes are not Bipedal 1 (Poor) This idea is perhaps weakest in proposing a realistic scenario to explain Pan-Homo-Gorilla divergence.    
2.4 Extant Analogues 8 (Good) This kind of behaviour is often seen in extant apes.    
2.5 Applies to Both Sexes 9 (Good) This model applies equally to both sexes.    
3.1 Hominid Anomalies 3 (Poor) These ideas do not set out to explain the postcranial anatomical anomalies of the australopithecines.    
3.2 Fits Paleoecological Record 8 (Good) The currently accepted ecological paradigm for human evolution is very compatible to this model.    
3.3 Precursor to Strider and knuckle Walker 5 (Fair) This model was rated neutral by this criterion.    
4.1 Extended Explanatory Power 4 (Fair) This model was rated slightly lower than neutral by this criterion because it is tied so closely to extant ape behaviour.    
4.2 Complimentary 7 (Good) This model was judged complimentary to most ideas, especially carrying and arboreal ones and compatible to the others.    
4.3 Falsifiable or Testable 3 (Poor) Proponents have not made any falsifiable predictions about this idea.    
References Hunt, K.D (1994) The Evolution of human bipedality: ecology and functional morphology. Journal of Human Evolution 26:183-202.
Pickford, M (1991). What caused the first steps towards the evolution of walkie-talkie primates?. In: Coppens, Yves; Senut, Brigitte (eds.), (1991). Origine(s) de la bipedalie chez les hominides. CNRS (Paris).br /> RRose, M D (1977). Positional Behaviour of Olive Baboons (Papio anubis) and its Relationship to Maintainance and Social Activities. Primates Vol:18(1) Pages:59-116.
Wrangham, R (1980). Bipedal locomotion as a feeding adaptation in gelada baboons, and its implications for Hominid Bipedality. Journal of Human Evolution Vol:9 Pages:329-331.