3.4.3: GENERAL SCAVENGING / HUNTING Shipman (1986), Sinclair et al (1986)		Home
Classification: Feeding Models Mnemonic: Hand to Mouth
Specific Model:	General Scavenging/Hunting
Original Proponent(s):	Shipman (1986), Sinclair et al (1986)
Basic Summary:	Scavenging and hunting for meat and then carrying it back to 'base camps' has long been a well accepted idea about human evolution. Here, two specific papers about it are reviewed. Greatly overlaps with similar carrying models.
Assessment:	Popularity: Feeding Models were ranked 2nd (out of 9) most popular in the texts reviewed. Simple: #27 (=5) / 42 (49%) Detailed: #26  (=2) / 42 (53%)
Discussion:	Shipman’s paper was offered, by Rose (1991), as an example of an argument in favour of scavenging being a major factor in the evolution of hominin bipedalism. However, from the outset, Shipman made it clear that the timescale considered for a scavenging life scale is as recent as 2 – 1.7 mya. This is far too late, of course, to have acted as a factor in hominid bipedal origins unless the proposed selective pressure discussed has its behavioural roots much earlier. The paper is considered here on this basis alone. Basically, the paper carefully evaluates the hypotheses that bovid faunal remains associated with Olduwai hominids were killed as a result of hunting or scavenging. It concluded that although there was evidence that some animals showed signs of being killed as a result of a more modern hunting technique, most appear to have bone scarring symptomatic of scavenging. This was offered as evidence that scavenging, not hunting was the likely main causal factor for the process of homininization and its characteristic bipedalism. The energy costs of scavenging, based largely on known figures modern humans, is estimated and the biomass of meat which could have feasibly been scavenged is estimated from the faunal remains of the Olduvai site, taking account of competition from other scavengers and predators, also estimated from the faunal remains. On this basis Shipman suggests that “all tests of predictions of the scavenging hypothesis given here are fulfilled by a generous margin. It is concluded that the scavenging hypothesis is not refuted and is worthy of additional investigation” Shipman (1986:37.) The paper concludes: “Finally, why bipedalism arose is a classic issue. The striking congruency between the attributes of bipedalism, as analysed here, and the locomotor needs of scavengers might suggest that some of that bipedalism is actually an adaptation, not an exaptation (Gould and Vrba 1982), to scavenging. If it is to be concluded that the origins of bipedalism and scavenging are causally related, one must be pushed back to more closely approximate that of bipedalism or it must be postulated that effective scavenging was possible without dental or technological adaptations for carcass processing.” Shipman (1986:38) Indeed, the timescale associated with the evidence presented here by Shipman is probably its biggest problem. The Olduvai hominids were clearly already well adapted to bipedal locomotion and probably had been for at least two million years. Even if they did practice a great deal of scavenging and their mode of locomotion was well adapted to it, this falls short of providing good evidence that scavenging was a major causal factor in its early adoption. The assumptions generally running through the paper, and specifically in the calculations used to estimate the plausibility of the scavenging model, are based upon the energy efficiency of modern human bipedalism and the understanding that the earliest bipeds walked as we do. Even if it was correct to hold such assumptions at 1.7 – 2.0 Ma, there must have been a time, more distant, before this when that locomotor efficiency was different, and probably worse. Therefore the main problem with the scavenging model is its ‘teleological’ nature: it proposes that clear benefits of modern human bipedalism, once the anatomy which makes them possible had evolved, were the likely drivers of its early evolution, even before such anatomical traits could have been present. Sinclair et al (1986) "Migration-Carrying" Hypothesis has been covered elsewhere but was also in support of this very much overlaping hypothesis.
Strengths:	When placed in the context of more open habitats this model does seem to make sense in terms of what early hominins could feasibly have been doing.
Weaknesses:	As with many models of bipedal origins which assume that a modern use of bipedalism was a driver of its evolution, it can be argued to be somewhat teleological. It also places early hominins under greater threat of predation.
Evaluation:/td>
1.1 SSurvival Value	6 (Fair) Like the migration carrying hypothesis, this was judged slihtly better than neutral on this criterion.
1.2 a href="DSS.html">SSexual Selection	6 (Fair) This modek was judged neutral on this criterion.
1.3 a href="DNT.html">NNot Teleological	3 (Poor) Scavenging/Hunting and carrying food bipedally seem natural to us but it is not as clear that this factor could have driven its evolution.
2.1 a href="EIF.html">IImproved Food Acquisition	8 (Good) Assuming that food procurement would have been improved by this behaviour, the model was rated good here.
2.2 a href="EAP.html">AAccounts for Predation	0 (Poor) This model appears to place early hominins in increased danger from predation as carrying meat would have both made them more attractive to predators and more vulnerable to them at the same time.
2.3 a href="EAN.html">WWhy Apes are not Bipedal	5 (Fair) This model was judged neutral by this criterion. It was judged weaker than the 'migration-carrying' hypothesis specifically as that model proposed a specific and plausible way of life that could have resulted in the divergence of one great ape lineage. This one is less clear cut.
2.4 a href="EEA.html">EExtant Analogues	4 (Fair) Conversely, this model was rated higher than the 'miration carrying' model as general scavenging behaviour is more often seen in extant apes.
2.5 a href="EBS.html">AApplies to Both Sexes	8 (Good) Scavenging applies to both sexes.
3.1 a href="PEH.html">HHominid Anomalies	5 (Fair) This model was rated neutral by this criterion.
3.2 a href="PPR.html">FFits Paleoecological Record	4 (Fair) This model was rated lower neutral by this criterion because it is largely based on open plains habitats that have been increasingly discredit by recent findings. The evidence for scavenging appears to be too late in the fossil record to support this model.
3.3 a href="POW.html">PPrecursor to Strider and knuckle Walker	5 (Fair) This model was rated neutral by this criterion.
4.1 a href="EEE.html">EExtended Explanatory Power	5 (Fair) This model was rated neutral by this criterion.
4.2 a href="ECM.html">CComplimentary	6 (Fair) This model is compliemtary to most carrying models and those set in  more open habitats. It was judged incompatible with most arboreal models.
4.3 a href="EFT.html">FFalsifiable or Testable	2 (Poor) The proponents of these models have rarely made any falsifiable predications.
References	Shipman, P (1986). Scavenging or Hunting in Early Hominids: Theoretical Framework and Tests. American Anthopologist Vol:88(1) Pages:27-43. Sinclair, A R E; Leakey, M D; Norton-Griffiths, M (1986). Migration and hominid bipedalism. Nature Vol:324 Pages:307-308