A Helping Hand (and foot): How the morphology of the hand and bipedal locomotion allowed humans to exploit novel resources and become successful

C.D. Stiegler – 1

A Helping Hand (and foot): Howthe morphology of the hand and

bipedal locomotion allowedhumans to exploit novelresources and become

successful

Christopher D. StieglerDepartment of Anthropology

University of [email protected]

ANTH 4309/Dr. Claire TerhuneMammalian Evolution & Osteology

12/14/2014

C.D. Stiegler – 2

Abstract

For all the differences between cultures, medicine is a

common theme. Medicine can be religious, symbolic, or

ritualistic. Another theme is that cultures are composed of

humans (H. sapiens) and they all require resources to survive. The

idea behind this paper is that all medicines started out as

dietary resources and that bony anatomy as much as olfaction,

energetics, visual acuities, and et. cetera, played a vital role

in the attainment of these resources. To understand how anatomy

allowed humans to exploit so many resources, their skeletal

anatomy is compared to the skeletal anatomy of other non-human

primates, raccoons, bears, and pangolins. Specifically, the

styloid process of the third metacarpal, opposability of the

C.D. Stiegler – 3

thumb, and adaptations for bipedalism are considered. Each of

these gave humans a greater precision grip and therefore the

ability to exploit a greater variety of resources, including

fragile underground storage organs (USOs). Innovations such as

tool use were used in concert with precision grips to do so.

This study concludes that humans have unique adaptations compared

to other mammalian taxa that allowed them to exploit novel

resources. Anatomy allowed humans to outcompete all other

mammals to reach the pinnacle of resource availability. This

research underlines the importance of understanding how evolution

shapes the wide variety of human dietary behaviors.

C.D. Stiegler – ANTH 4309 – Dr. Claire Terhune – 12/14/14 –University of Arkansas, Fayetteville, AR – Dept. of Anthropology

A Helping Hand (and foot): How the morphology of the hand andbipedal locomotion allowed humans to exploit novel resources and

become successful

C.D. Stiegler – 4

Introduction

Medical anthropology studies the relationship between humans

and medicines that are culturally, symbolically and ritually

important to them. Many of these relationships stem from a

traditional knowledge of local ecologies and often complement

what is rediscovered by biomedicine (Bakx, 1991). That cultures’

traditional knowledge equates with Westernized medicine suggest

an evolutionary heritage with humans and the plants used in both

traditional medicine and pharmacology. Furthermore, it is

postulated that the origin of the hominin diet of plants cascaded

a co-evolutionary relationship between the taxa. This led plants

to eventually be coopted as viable medicinal resources (Johns,

1996). Today, humans use a variety of dietary behaviors,

including folivory, frugivory, granivory, carnivory, et cetera

for both food and medicine. Such a varied diet gave humans an

evolutionary advantage over other mammals (Laden et.al, 2005).

However the

question remains, what allowed humans to exploit novel resources

and have this competitive advantage? Why weren’t other mammals

able to do the same? While factors such as olfaction, visual

C.D. Stiegler – 5

acuity to color, and increased intelligence played an important

role (Sekuler et. al, 2005), anatomy also allowed humans the

ability to exploit novel resources within their environment.

Laden

(2005) suggest that resources, commonly known as underground

storage organs (USOs), were the novel resource that gave humans

and their ancestors a competitive advantage over other mammalian

taxa. Morphological adaptations of the hand and hind limb

allowed the exploitation of resources other mammals could not

exploit. These adaptations include the styloid process of the

third metacarpal, the presence of an opposable thumb, the width

of the metacarpal, position of the foramen magnum, the lumbar

lordosis, a valgus knee, the size and shape of the pelvis, and

arches of the foot. All of these collectively allowed humans to

exploit new resources, such as fragile USOs, and become more

successful than other mammals. This paper will

compare these adaptation in humans (Homo sapiens) to other

mammalian taxa, and these differences will shed light on why

humans were able to exploit resources other mammals were not.

The non-human mammals analyzed in this paper are the great apes

C.D. Stiegler – 6

(family: Hominidae), bears (family: Urisidae), pangolins (order:

Pholidota), and raccoons (order: Carnivora). Obviously, these

four taxa do not cover all the extant clades of mammals, but were

each chosen for a specific reason. The great apes were chosen

because of their close ancestry and common evolutionary history

to humans. Many of the adaptations observed in the great apes

are sympleisiomorphic with humans (Andrew, 1987). Bears and

raccoons were selected because they manipulate their dietary

resources with their anterior “hands” (Iwaniuk et. al, 1999;

Laden et. al, 2005). Pangolins were used not only because they

manipulate food with their anterior “hands” but also because they

generally walk bipedally (Mohapatra et. al, 2014). The

comparison of humans to these mammals will illustrate why the

unique characteristics of human anatomy are important in

understanding humans’ ability to exploit resources not exploited

by other mammals.

C.D. Stiegler – 7

Morphology of the hand

The styloid process of the third metacarpal is a feature

unique to humans when compared to other extant mammals (Ward et.

al, 2013). This process locks the third metacarpal more securely

to the capitate bone for greater amounts of pressure in grip

(Ward et. al, 2013). However, Ward (2013) suggest this styloid

process is not observed in any mammalian taxa at least until

Homo with possible precursors in australopithecines. Of the

mammalian taxa used in this analysis, raccoons and great apes

have the most “human-like” hand (Walker, 1995). Pangolins and

bears display a parallel thumb (DePanafieu et. al, 2011).

Specifically, raccoons and great apes have divergent

thumbs, used for grasping and manipulating food (Salesa et. al,

2009; Almecija et. al, 2010). However, they lack a styloid

process and according to Ward (2013), the function of this

structure rest in a precision grip. Therefore, while raccoons

and great apes may have a divergent thumb adapted for grasping,

without the styloid process, they lack any form of “human-like”

precision. Secondly, non-human primates, including

the great apes, do not have fully opposable thumb (Young, 2003).

C.D. Stiegler – 8

Unlike humans, “The typical primate hand is characterized by a

diminutive thumb in combination with long, curved fingers”

(Young, 2003 p. 165). Furthermore, none of the non-primate

animals in this analysis have an opposable thumb either.

Obviously, the presence of an opposable thumb is an important

part of precision grip (Almecija et. al, 2010). Specifically,

while raccoon hands are “human-like,” their thumbs lack

adaptations for opposability, though they are still able to

inspect food by manipulating it in their hands (Walker, 1995).

It is much more difficult for them to do what is called Form

Closure which prevents the object from moving around in the

animal’s hand (Walker, 1995). Therefore, raccoons are more

likely to lose an object after grabbing it than humans.

While the raccoon’s thumb is not as opposable as

humans, it is still more dexterous than the hands of bears and

pangolins. The bears’ thumbs is simply parallel without a lot of

movement (DePanafieu et. al, 2011). Within the urisids, only

pandas have an opposable “false thumb” (Salesa et. al, 2005).

This false thumb is not as effective as the actual opposable

thumb in humans. Salesa (2006, p. 390) states about the sesamoid

C.D. Stiegler – 9

bone of the first metacarpal (the thumb), “In general, sesamoid

bones are small, more or less rounded masses embedded in certain

tendons and usually related to joint surfaces, their functions

being to modify pressure, to diminish friction, and occasionally

to alter the direction of a muscle pull (Gray, 1977). The radial

sesamoid of pandas lost these primary functions, becoming part of

a pincer-like complex related to the manipulation of food.”

Therefore, urisids hands are not as efficient at precision as

human hands.

Pangolin hands do not have adaptations for precision by

means of an opposable thumb (Mohapatra et. al, 2014). Instead,

they have fossorial adaptations in their anterior limbs, used for

digging up ant mounds, and feed on as many scattered ants a

possible (Mohapatra et. al, 2014). Neither bears nor pangolins

have to manipulate their food without any precision from the

thumb. Another unique feature of the human hand is a

thicker metacarpal head in relation to other great ape and mammal

species, with the exclusion of Pan (Susman, 1998). The thicker

metacarpal tips allow for a greater amount of precision, which

Susman (1998) claims are observed as early as Australopithecus. He

C.D. Stiegler – 10

suggest that these animals had the full capability of modern

humans for a precision grip.

In contrast with other primates, humans have a

much thicker metacarpal, much shorter fingers and, as mentioned

before, a fully opposable thumb; all leading to a greater

precision grip (Young, 2003). Ergo, with the absence of these

features, non-human primates, such as the great apes, do not show

such a complete precision grip.

While the thickness of the metacarpals in raccoons has

not been measured for precision, Walker (1995) explains that

raccoons’ phalanges have a greater range of motion than humans.

Therefore, their hands are not as firm and not as efficient at

precision grips. Rather than using a precision grip, raccoons

manipulate their food with two hands between their palmar pad and

the distal ends of the phalanges (Iwaniuk et. al, 1999). Their

precision is similar to humans but not nearly as effective.

Bears have

thick and hefty metacarpals (Toskan, 2006). However, their body

size is massive, weighing in at 600kg (Dewey et. al, 2002 –

Animal Diversity Web) denying them the ability to use precision


grip in their anterior hands (Laden et. al, 2005).

No research was found specifically on the thickness of

the pangolin metacarpal head. All that can be said is to

reiterate that they are digging for ants (Mohapatra et. al,

2014). They have no interest in exploiting resources that

require precision, such as fragile USOs. Like the

styloid process of the third metacarpal, thickness of the

metacarpal heads leads to more dexterity and precision. With

wider metacarpal heads, the trend would be more dexterity and

precision. With these anatomical features, humans have the best

adaptations for precision grip and dexterity. Therefore,

raccoons, bears, great apes and pangolins have grips whom

precision is not as efficient as that seen in modern humans.

How does all of this relate to

exploiting new resources, such as difficult to attain and fragile

underground storage organs? The answer lies in the

aforementioned anatomy. Dexterity and precision allows humans to

do something much more efficiently than other mammalian taxa.

These adaptation allow for the ability of tool use which is

dependent on precision and dexterity. Although the first tools


were only flakes and cores from 3.2 million years ago, the fact

that they were mass produced suggest quite a large amount of hand

dexterity and precision (Panger et. al, 2003).

Throughout

evolutionary history, stone tools were used for a whole host of

purposes (Keeley et. al, 1981). Most commonly, they are

associated with hunting. However, while stone tools were

prevalent in hunting strategies, they were also used to gather

botanical resources (Keely et. al, 1981). Specifically, they

must have been used to gather USOs including small, fragile roots

which are used today in a variety of dishes worldwide. Some of

these resources are very robust, and others quite gracile such as

plants from the genus, Peucedanum (Laden et. al, 2005). Plants

that are fragile must be pulled out of the soil with care. The

dexterity and precision the styloid process, narrow metacarpals

and opposable thumbs give humans help them to exploit the more

fragile USOs. This gave them a competitive edge over other non-

human mammalian taxa (Laden et. al, 2005).

Without these adaptations of the hand for

precision and dexterity, raccoons, bears, great apes, and


pangolins are not be able to exploit the more fragile USOs.

Bears only forage more rigid USOs (Laden et. al, 2005) due to

their lack of dexterous hand adaptations, and their massive body

size. They would crush the more fragile USOs before ever

exploiting them. Raccoons only share with humans a divergent

thumb (Iwaniuk et. al, 2009). They lack any styloid process,

opposable or narrow metacarpals for dexterity and precision.

Humans’ uniqueness from other mammals allowed

them to outcompete, giving them a wider variety of resources. A

comparative analysis of human anatomy and non-human mammal

anatomy illustrates nicely why the human hand helped humans to

exploit novel resources.

Bipedalism

Humans, unlike all other extant mammals, are habitual bipeds

(Schmitt, 2003). This means they are anatomically forced to move

through their environment on two legs. Specifically this is a

derived trait from great apes, raccoons, bears, and pangolins.


Well, to be fair, pangolins are bipedal as well, but their form

of bipedality differs from humans (Mohapatra et. al, 2014).

While it is unclear when bipedalism first appeared,

anatomical evidence from Ardipithecus ramidus suggests it was at

least four and a half million years ago (Lovejoy et. al, 2009).

Over millions of years, bipedalism evolved into its present form,

conserving as much energy as possible (Sockol et. al, 2007). As

a byproduct of its evolution and low energetic cost, bipedalism

allows humans to exploit more resources by freeing up their hands

and making it easier to move around the environment (Hewes,

1961). An important precursor to the

energy conservation of bipedalism are the anatomical adaptations

that allowed humans to conserve that energy in the first place.

These include the position of the foramen magnum, the lumbar

lordosis, the valgus knee, the size and shape of the pelvis, and

arches of the foot. These adaptations can be compared to what is

observed in great apes, raccoons, bears, and pangolins to

illustrate why the adaptations gave humans the competitive

advantage over other mammalian kin.

The foramen magnum is a feature of the inferior part of


the cranium. It is a hole in the occipital bone where the spinal

cord inserts and passes through to the brain (Ahern, 2005).

Compared to humans, great apes, raccoons, bears and pangolins all

have a posteriorly placed foramen magnum (Ahern, 2005). The

position of the foramen magnum is a byproduct of an organisms’

locomotion. For those that are quadrupedal, the more posteriorly

placed foramen magnum allows them to see directly in front of

them because the spine is placed posterior to the skull. In

bipeds, the foramen magnum is more anterior, placing the spinal

directly inferior of the neurocranium. This allows bipeds to see

directly in front of them. In the trees,

gorillas, chimpanzees and orangutans need stereoscopic vision for

moving around in the trees, grasping from branch to branch

(Heesy, 2009). For raccoons and bears, stereoscopic vision is

important for hunting (Sekuler et. al, 2005) as they are members

of the order Carnviora. In pangolins, it is important for picking

up ants (Mohapatra et. al, 2014). Stereoscopic vision places the

eyes more medially towards the rostrum creating depth perception,

needed for both arboreal locomotion and hunting (Sekuler et. al,

2005). This is why it is important for the animal to see


directly in front of them. If their foramen magnum was oriented

more anteriorly like in humans, they would have no option but to

look directly downward. Although pangolins are more bipedal than

the other mammals, their foramen magnums are not as anteriorly

placed as in humans and their ancestors (Gaubert et. al, 2005).

Thus, they are not fully bipedally.

Another characteristic of bipedalism is the lumbar

lordosis. The great apes, pangolins, bears, and raccoons all

have dorsally orientated and straight vertebral columns, while

humans and their bipedal ancestors have a lordosis of the lumbar

vertebrae (Whitcome et. al, 2007). The non-human mammalian

vertebras are more condensed, and therefore not as flexible for a

variety of movements (Lovejoy et. al, 2009). The purpose of

this more flexible osteological marker is to support all the

weight from the body superior to the axial plane. Because all

the weight is housed on the posterior limbs in humans, rather

than distributed evenly on all fours limbs like in other mammals,

the vertebral column has to adjust; similar to a slinky bending

as a child adds weight to the top of it (DePanafieu et. al,

2011). Thirdly, pelves between


human and other mammals are also different due to bipedality

(DePanafieu et. al, 2011). Chimpanzee pelves are much more

gracile and horizontal, running along the coronal plane. Human

pelves are more robust and have an ilium curved medioanteriorly

into the sagittal plane (DePanafieu et. al, 2011). Over

evolutionary time, nature selected this morphology for bipeds due

to an increased surface area and leverage for larger stabilizing

adductors and abductors such as the gluteal muscles (Hunt, 1994).

Like chimpanzees, the pelves of the rest of the great apes,

raccoons, bears and pangolins are thin and orientated along the

coronal plane (DePanafieu et. al, 2011). Thus, none of these

animals, including the pangolin, has the adaptations needed for

the most energetically efficient bipedality. Fourthly,

valgus knees are oriented whereas the distal end of the femur is

medial while the proximal end is lateral (Schmitt, 2003). This

is observed in humans to help support all the weight superior to

the axial plane (Schmitt, 2003). This characteristic is not

observed in any other primate or mammalian (i.e. – raccoons,

pangolins, and bears) species (DePanafieu et. al, 2011), or even

humans’ closest relatives, the chimpanzees and gorillas (Jenkins


Jr, 1972). Their knees and femurs are orientated directly

ventrodorsally because their body weight is distributed evenly on

all four limbs. They do not need this adaptation of bipedalism.

Finally, arches of the foot in humans

also indicate bipedality. Human feet have three arches,

including the anterior transverse arch, the lateral longitudinal

arch, and the medial longitudinal arch, which are not present in

other mammal and primate taxa (Susman, 1983). For example, non-

human primates such as gibbons, gorillas, orangutans, and

chimpanzees walk on the lateral side of their foot (MacConail,

1944/1945; Allen, 1997; D’Aout, 2009). Humans have evolved the

three arches so that they can accomplish both heel-strike and

toe-off (Wang et. al, 2001) and help to propel all of the body

weight forward. The only other

animal in this analysis that walks bipedally is the pangolin.

Yet, unlike humans, it uses its tail to balance on its two hind

limbs (Mohapatra et. al, 2014). The weight is not distributed

only on the two hind limbs but on all four, which explains why

the pangolin does not have anatomical features such as a more

anterior foramen magnum, a more robust pelvis, a lumbar lordosis


and foot arches. Because of this, the pangolin is not as

efficient at exploiting resources as species of hominin.

Bipedalism is

important in food procurement because according to Hewes (1961),

these adaptations freed up the anterior limbs for the evolution

of precision grip and tool use. Humans have adaptations in their

posterior limbs that allow them to become obligate bipeds while

other mammals can only be at best facultative bipeds. As anatomy

changed, bipedalism allowed humans to use tools and become more

efficient at foraging fragile USOs. With hands came precision in

the hands and the ability to use tools.

Also importantly, USOs are more prevalent in savannas

than rainforest (Laden et. al, 2005). Since bipedalism is

energetically less expensive than quadrupedalism (Sockol et. al,

2007), mammals that display it are likely to be more efficient at

exploiting USOs. Great apes will likely stay in their forest

range due to their energetically costly quadrupedalism (Sockol

et. al, 2007). Bipedalism does not cost as much energy for them

to travel from the rainforest and woodland out into the savanna.


Therefore, it gave humans and their bipedal ancestors a

competitive advantage over their mammalian kin.

Conclusion

This referential study illustrates how humans are unique

amongst the mammal clade. Anatomically, the hand and forelimb

differed and allowed for the evolution of a precision grip and

tool use. These anatomical features include the styloid process

of the third metacarpal, thumb opposability, the thickness of the

metacarpal head, the position of the foramen magnum, the lumbar

lordosis, the shape and size of the pelvis, the valgus knee, and

the arches of the foot. These tools allowed the more efficient

exploitation of fragile underground storage organs amongst other

things. The presence of each of these adaptations also allowed

humans to acquire bipedalism, which is a more energetic mobility

behavior. It also freed up the hand and allowed the adaptations

in the hand for precision grip used in tools. The ability to

exploit previously non-exploitable resources likely gave humans

and their ancestors a competitive advantage over other mammalian

taxa, such as the great apes, raccoons, bears, and pangolins.


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A Helping Hand (and foot): How the morphology of the hand and bipedal locomotion allowed humans to exploit novel resources and become successful

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