Are Cultural Or Biological Adaptations Responsible for What Makes Us Human

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Genetically we could say that for humans, evolution has stopped (Hendry, 2012). However, cultural adaptations involved in evolution cannot be ignored, as the complex relationship between biological and cultural adaptations has existed since the first stone tools of East Africa 2.6 million years ago (mya). I will argue that, following the reliance of H. ergaster on cultural adaptation 2 mya, evolution has involved more cultural adaptations than biological, as cultural adaptations such as fire and clothing meant there wasn’t a need for biological adaptations.

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H. sapiens are distinct in that they occupy the largest geographical and ecological range of any terrestrial vertebrate (Boyd et al., 2013). In order to do so, our ancestors had to adapt to a vast range of environments, from hot, dry deserts to glacial arctic wasteland. Henrich (2017) uses cases of expeditioners to support his argument that it is not our inherited intelligence which makes us successful, but our culture. Burke and Willis’ expedition 1860CE, for example, shows that they would not survive as hunter-gatherers as they did not possess the intelligence or instincts to survive while trapped along Coopers Creek. The expeditioners did not possess the skillset and instincts that allow locals to survive, which is passed through generations via socialisation and modelling in order to thrive in the specific habitat. This knowledge includes identifying plants such as Marsilea drummondii (nardoo), an aquatic fern which aboriginals processed to make bread, but is found to be toxic with Thiaminase, causing B1 depletion. Despite extensive preparation, it is suspected that Burke and Will’s died from starvation and consumption of improperly detoxified nardoo seeds (Henrich and McElreath, 2003). Natural experiments ethically demonstrate how foraging adaptations are beyond individual’s usual capacities. To inhabit a diverse range of habitats as we uniquely do as H. sapiens, biological adaptations such as increased brain size allowed us to develop cultural solutions and pass these on through generations.

Non-human primates help uncover whether our traits are genetic or cultural. For instance, P. troglodytes in the Mahale Mountains National Park, Tanzania (as shown in Figure 1) groom each other by lifting one arm and clasping each other’s raised arms, then grooming one another with their free hands (Read, 2012). Only P. troglodytes in this region groom in this way, indicating that this trait is not passed on genetically but through individuals culturally. P. troglodytes in the Taï Forest of West Africa demonstrate behaviours indicating they understand group intentions (Boesch and Boesch-Achermann, 2000, as cited in Shipton, 2010). Brutus, an alpha male, was observed banging the roots of trees in order to change his group’s direction or to declare rest breaks using drumming sequences and the tree’s location, showing understanding of how to control other’s behaviour and that others knew his intentions. Taï P. troglodytes also perform ant dipping with a 30cm stick, dipping until soldier ants cover a third of the stick before swiftly cleaning them off the stick. This behaviour is different among chimps in other regions, such as Gombe, suggesting it is a learned behaviour within this group and therefore is cultural rather than biological.

Technology has been key to the process of adapting to a range of diverse environments (Boyd et al., 2013). To simply obtain food required tools including spears, bow and arrow, and atlatls to hunt game, flaked stone tools to process, as well as materials to make fire for cooking. Stone tool use is a profound cultural adaptation, with the first Oldowan assemblages emerging around 2.6 mya during the Lower Palaeolithic in East Africa, presumed to be used by Homo habilis (Hendry, 2012, De la Torre, 2011). Although it is not explicit when stone tools first appeared, in 1997 the earliest definite stone tools found in Gona were dated back to 2.5 mya (De la Torre, 2011). Permitting our ancestors to manipulate the environment allowed for subsequent behavioural revolutions (Hendry et al., 2012). Acheulean assemblages- distinctive bifacial hand axes and cleavers- have been found in various regions, giving us great reason to suggest imitation and intentionality were present among various Acheulean sites displaying the same strategies (Shipton, 2010). As shown in Figure 2, the shapes of the bifaces imply that hominins of the Isimila stone age site, for instance, possessed intention and concept. It is reasonable for us to conclude that such complex tool making behaviours were transmitted between hominins- a demonstration of early cultural adaptation to deal with problems within the environment and transmit solutions.

On the contrary, it is argued that biological adaptations are most profound in the way H. sapiens have developed. The process of bipedal locomotion, for example, is an essential biological adaptation to survival and reproduction (Gruss, 2015), showing the relationship between genes and the environment (Hendry, 2012). The transition from quadrupedalism (primarily walking on four limbs) to bipedalism (walking on two legs) required changes through the body. Examination of skeletons of our ancestors can establish locomotion by understanding how their muscles were supported. Although spending long periods climbing trees, Sahelanthropus tchadensis demonstrated the first signs of bipedalism, occurring approximately 7 mya. The modern configuration of walking, however, was more likely to have appeared with H. ergaster, as a response to the savannah environment.

[image: ]Supplementing bipedalism, the evolution of our pelvic anatomy is key to understanding our current anatomical condition (Gruss, 2015). Our pelvis allows us to walk efficiently with low injury risk, as well as influencing thermoregulation where our proportions alter the body’s heat loss. Figure 3 depicts bi-iliac breadth which regressed on acetabular height (Holiday, 2012). The regression lines of H. sapien and P. troglodytes are almost parallel, although P. troglodytes have wider bi-iliac breadth no matter their acetabular size, which is not the same for H. sapiens. The shortened height and blade of the ilium of H. sapiens compared to P. troglodytes (as shown in Figure 4) lowers the centre of mass for the P. troglodytes (Gruss, 2015). The laterally positioned iliac blade and wider sacrum in H. sapiens allows for gluteal muscles, which are external of the ilium, to prevent the pelvis from tipping, demonstrating the adaptation of the pelvis to possess the stability to transition to bipedalism.

The adaptation of the pelvic anatomy was essential to allow the birth of human babies without extreme pain for the mother during delivery, as the birth canal’s proportions are a result of the lower pelvic structure (Gruss, 2015). Figure 5 depicts the differences between infant’s head positions at the three planes of the birth canals of P. troglodytes, Australopithecus afarensis (specifically ‘Lucy’, or A.L. 288-1) and a modern female H. sapien. For the P. troglodytes, the infant’s head is facing anteriorly through each stage, while the A. afarensis infant’s head faces laterally with a non-rotational pattern, and the H. sapien infant’s head begins laterally at the inlet, rotates at the midplane and exists the outlet posteriorly. Rak (1991, as cited in Gruss, 2015) investigated the relationship between pelvic rotation and stride length, finding shorter legs, as seen with Australopithecines, demonstrate increases in pelvic rotation when walking quickly. Whitcome et al. (2012, as cited in Gruss, 2015) support this as they found that women have bigger strides than men due to wider pelvises. A broad pelvis may be beneficial as this increases the flexibility of speed in relation to locomotor costs when being short legged (Wall-Scheffler et al., 2007, as cited in Gruss, 2015). An increase in environmental variation additionally meant that thermoregulatory adaptation was required for Homo. By developing the body we share today, we were able to live in various environments and have learnt to find cultural solutions when these are needed.

Our unique ability to contemplate our existence and develop complex killing methods, sparks the question of what it is about our nervous system that makes us different (Falk, 1980). Australopithecus had an average brain size of 450cc, while H. ergaster was approximately 1400cc, and H. sapien around 1350cc (Hendry, 2012). Keith (1948, as cited in Falk, 1980) proposed ‘cerebral rubicon’, where apes and Australopithecines are separated from Homo. The brain growth which appeared with the presence of Homo at the beginning of the Pleistocene and end of Pliocene is greater than can be explained by the increase in body size (Lee, 2003). By developing food-gathering methods, the body was fuelled for subsequent expansion of the brain, which required a frequent supply of calories (Hendry, 2012). This led to stone tools appearing around 2.5mya, allowing effective butchering of carcasses to further supply our pronounced brain size.

Considering the evidence provided throughout this paper about what makes us human , the most consistent and logical argument appears to be that whilst we previously relied heavily on biological adaptations, we now rely most on cultural (Hendry, 2012). Succeeding H. ergaster 2 mya, cultural adaptations were most relevant, arguably after the first stone tools were introduced. As H. sapiens developed stone tool technology, biological adaptations became less necessary as we were, and still are, able to produce the tools or methods required to survive, which we culturally reproduce generationally.



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