Pliny The Elder

It was once thought that human evolution had progressed in a linear and stepwise fashion, from simpler to more complex forms, culminating in H. sapiens. However, as the fossil record has grown, it has emerged that a diverse assemblage of hominids existed in the past, some of which were ancestral to humans, whilst others occupied separate branches of an extensive evolutionary tree. The relationships between these fossil forms have occasioned much debate among palaeontologists and will, doubtless, continue to do so. The arrangement shown in Figure 1.1 should be regarded only as a summary of current knowledge, as the hominid tree will certainly expand and change in the future.

Firstly, at the base of the tree, whose African roots include the common ancestors of humans and chimpanzees, are several fossil ape genera, known only from fragmentary remains: Sahelanthropus, Orrorin, and Ardipithecus (Stringer and Andrews 2005; Sawyer and Deak 2007).

A single cranium of Sahelanthropus tchadensis has been discovered; it exhibits hominid features such as a flat vertical face, small canines, and a foramen magnum situated on its undersurface, possibly indicating that the head was held in an upright position. However, no parts of the postcranial skeleton are available, and it is not known if this animal walked upright. It existed in the Saharan region, in what is now Chad, about 7 MYa. Its brain was quite small (360 cc), and certain features of its nasal anatomy indicate that it may have pre-dated the common ancestors of chimpanzees and humans (Brunet et al. 2002; Lebatard et al. 2008). Hominid affinities of the skull have been reinforced by the results of studies using CT scans (Zollikofer et al. 2005).

Even less well known is Orrorin tugenensis which occurred in Kenya about 6 MYa. Only some jaw and limb fragments of this ape have been described, and although there has been speculation that it may have walked upright, there is insufficient information to reconstruct its locomotor patterns. Ardip-ithecus is likewise only known from fragments of its jaws and postcranial skeleton. Two species have been described: A. ramidus (4.4 MYa) and A. kadabba

H. sapiens H. neanderthalensis

H. sapiens H. neanderthalensis

Sexular Selection

Figure 1.1 Approximate time spans and evolutionary relationships of the main hominid taxa. Please note that the abbreviation "A" is used for the genus Ardipithecus (ie A. kadabba and A. ramidus) and for members of the genus Australopithecus. Further details are given in the text. Source: Based upon information in Tattersall and Schwartz (2001); Wood (2001); Collard (2002), and Stringer and Andrews (2005).

(5.5 MYa). Ardipithecus, Sahelanthropus, and Orrorin occupy the base of the hominid lineage (Figure 1.1) from which the subfamily Australopithecinae and, ultimately, the genus Homo arose.

Five species of Australopithecus (literally 'southern ape') have been discovered, at widely separated sites in Southern, Eastern, and Central Africa (Australopithecus anamensis, A. afarensis, A. bahrelghazali, A. africanus, and A. garhi). These were relatively small-brained creatures (brain volume 400-500 cc), but with notably reduced canine teeth compared to those of modern apes. Australopithecus was capable of terrestrial, bipedal locomotion as well as being adept at climbing trees. Best known is A. afarensis (4.2-3.2 MYa), the most complete skeleton being that of 'Lucy' from Hadar, in Ethiopia (Johanson and White 1980; Johanson and Edey 1981). It displays an intriguing mixture of traits, such as long, curved fingers and toes, a funnel-shaped rib cage typical of apes, and a broad, short pelvis with some similarities to that of human beings (Figure 1.2).

Lucy may have weighed approximately 30 kg, but it has been argued that adult males of this species, and of some other australopithecines, were considerably larger than adult females. Table 1.1 includes estimates of body weight for adults of both sexes of various fossil hominids, as well as for modern H. sapiens. At 44.6 kg, males of A. afarensis were 1.52 times larger than adult females. If correct, this sex difference in body size would be consistent with effects of sexual selection, via intermale competition, such as occurs among extant

Figure 1.2 Reconstruction of the skeleton of Australopithecus afarensis (Lucy). Source: Author's drawings, after Johanson and Edey (1981).

monkeys and apes which have polygynous mating systems. Intra-sexual selection has favoured the evolution of body size sexual dimorphism in a variety of Old World monkeys, such as geladas (adult male: female body weight ratio = 1.6), hamadr-yas baboons (1.7), and proboscis monkeys (2.0) as well as gorillas (2.3). However, a major difference between all these species and the australopithecines is that intra-sexual selection has also resulted in the evolution of markedly larger canine teeth, as well as greater body size in males of the extant forms.

Why the australopithecines and all later fossil hom-inids have relatively small canines has not been explained. However, it is possible that some overriding selective process, perhaps connected with feeding ecology, might account for the reductions in canine size, and lack of dental sexual dimorphism in the australopithecines.

Estimates of body weights and of sexual dimorphism in the fossil hominids listed in Table 1.1 must be treated with considerable caution. Although such estimates are often cited in the anthropological

Table 1.1 Estimates of body size and sexual dimorphism in fossil hominids, and in modern Homo sapiens

Species

Body weight (kg)

Ratio

Adult male

Adult female

Male/Female

Australopithecus

44.6

29.3

1.52

afarensis

A. africanus

40.8

30.2

1.35

Paranthropus

48.6

34.0

1.43

boisei

P. robustus

40.2

31.9

1.26

Homo habilis

37.0

31.5

1.17

H. ergaster

63.0

52.0

1.21

H. erectus

63.0

52.5

1.20

H. neanderthalensis

73.7

56.1

1.31

H. sapiens

63.5

52.3

1.21

Source After Collard (2002), and based upon multiple sources.

Source After Collard (2002), and based upon multiple sources.

literature, it is by no means certain that all of them are accurate. The fragmentary nature of specimens of various fossil species renders problematic any attempt to measure body size. Even in the case of Lucy, one of the most complete specimens, less than 40 per cent of the skeleton was recovered. Much less is known about the postcranial anatomy of the other australopithecines. However, Alemseged et al. (2006) have described a more complete skeleton of an immature specimen of A. afarensis, from Dikika in Ethiopia. An almost complete skeleton of A. africanus has been partly recovered from Sterk-fontein in South Africa (Clarke 2002). Then there is the question of whether a particular specimen is from a male or a female, not a trivial problem when only small portions of the skull or skeleton may be available. Thus, in the case of A. afarensis, there are major differences of opinion among scholars concerning sexual dimorphism in body size. Reno et al. (2003) conducted a careful analysis of skeletal dimensions in this species, and reached the conclusion that it was not markedly sexually dimorphic. These authors therefore suggested that sex differences in body weight in A. afarensis were within the range displayed by modern humans and were consistent with a monogamous mating system, rather than with the occurrence of polygyny.

Although sex differences in body size are most pronounced in extant anthropoids which are polygynous, sexual selection, via inter-male competition, has also favoured the evolution of dimorphism among Old World monkeys and apes which have multi-male/multi-female mating systems. Sex differences in body size are not so extreme in these circumstances, as for example in chimpanzees, but it would be impossible using current estimates of body sizes in fossil hominids to exclude the possibility that some of them might have had multi-male/multi-female mating systems. Clearly, our ability to identify the likely mating systems of these early hominids on the basis of existing fossil evidence alone is very limited (Plavcan 2001).

It may be helpful at this early stage to define the various types of mating systems that occur among the extant primates, as the mating systems of extinct forms will be discussed in comparative perspective. Five mating systems may be recognized (Table 1.2) based upon two important considerations. Firstly, do females usually mate with one partner, or with multiple partners and, secondly, are these sexual relationships long term and relatively exclusive or short term and non-exclusive? Monogamy involves a long-term sexual relationship between a male and a female, whilst polygyny involves long-term sexual relationships between multiple females and a single male. Both these kinds of mating systems are widely represented among recent human cultures (Ford and Beach 1951) as well as among the nonhuman primates (Table 1.2). Polyandry (a long-term relationship between one female and several males) is exceptional, but it has been recorded for people in parts of northern India, and also in some of the New World monkeys (tamarins). In multi-male/ multi-female mating systems, by contrast, females mate with a number of partners in a more labile fashion, and the same is true for males, given the constraints of social rank and other limiting factors within groups. Sexual relationships are short term in such systems which occur in macaques, many baboons, and chimpanzees. Human beings do not exhibit this type of a mating system. Nor is the dispersed mating system (Table 1.2) found in human populations, as this is typical of non-gregarious nocturnal primates, such as mouse lemurs (Micro-cebus) which live in individual home ranges and engage in short-term relationships and multiple-partner copulations.

Table 1.2 A classification scheme for primate mating systems

Number of males mating per female cycle

Type of sexual relationship

Mating system

Examples

One

Long term, exclusive

Monogamy

Indri, Aotus, Callicebus, Hylobates, Homo sapiens

One

Long term, exclusive' but other females also mate with the resident male

Polygyny

Theropithecus, Papio hamadryas, Nasalis, Gorilla, Homo sapiens

Two or more

Long term, exclusive

Polyandry

Saguinus fuscicollis*, Callithrix humeralifer*

Two or more

Short term, not exclusive, gregarious

Multi-male/multi-female

Propithecus, Macaca, most Papio spp., Cercocebus Saimiri, Lagothrix, Pan

Two or more

Short term, not exclusive, non-gregarious

Dispersed

Microcebus, Daubentonia, most Galago spp., Perodicticus

'The single male mates with other females In the 'harem' unit.

'Monogamy also occurs in these callitrichid species, and is probably the primary mating system in many cases. Source: Modified from Dixson (1998a).

'The single male mates with other females In the 'harem' unit.

'Monogamy also occurs in these callitrichid species, and is probably the primary mating system in many cases. Source: Modified from Dixson (1998a).

Returning to the australopithecines, attempts have been made to reconstruct what the various species might have looked like in the living state. As an example, Figure 1.3 shows a reconstruction of A. africanus, the first of the 'southern apes' to be discovered (Dart 1925). This species occurred in Southern Africa, approximately 3.0-2.3 MYa and, like A. afarensis, it is thought to have been proficient at climbing as well as walking upright on the ground. It had relatively longer arms and shorter legs than Homo. In Figure 1.3, a male and female A. africanus are shown walking upright, in much the same way as human beings. There is no assurance that they moved in precisely the same way as we do, however, as they possessed a combination of locomotor traits not found in humans or in any existing primate species. This explains why so much controversy has surrounded attempts to interpret the locomotor and postural capabilities of the australopithecines; indeed some earlier scholars, such as Zuckerman, refused to accept that they might be ancestral to humans. As the anatomical evidence has accumulated over the years, it reinforces the conclusion that these creatures stood and walked upright, as well as climbing and using their arms for arboreal suspension and locomotion. At Laetoli, in Tanzania, well-defined tracks of australopithecine footprints have even been discovered, dated to about 3.5 MYa. These are thought to have been made by A. afarensis as they walked upright through an area covered in moist volcanic ash (Leakey and Hay 1979).

The external appearance of A. africanus, as depicted in Figure 1.3, is inevitably subject to much uncertainty. Surface morphology is heavily defined by traits which do not fossilize, such as the hair and skin. Extant African apes have dark skin due to deposits of epidermal melanin. Likewise African populations of H. sapiens are, typically, dark skinned, and it is thought that this would have been the case in the earliest human populations in Africa. Melanic pigmentation offers protection against exposure to high levels of UV radiation in the tropics (Jablonski and Chaplin 2000; Jablonski 2006). In Figure 1.3, A. africanus is shown as having much less hair on its body and limbs than today's chimpanzees or gorillas. There is no assurance that this is correct. As apes which lived in arboreal environments, as well as in more open, grassland conditions, it is possible that the australopithecines were more hirsute than is shown in Figure 1.3. Loss of hair may only have become pronounced in later hominids, in association with increased density of cutaneous sweat glands and other specializations to improve thermoregulation in large-bodied and

Australopithecine Sexual Dimorphism
Figure 1.3 What did the australopithecines look like? Reconstruction of Australopithecus africanus. The adult male is shown on the left. Source: After Tudge (2000).

Figure 1.4 Reconstructions of the skulls of robust australopithecines. or 'nutcracker man'). Author's drawings from photographs.

entirely bipedal terrestrial hunter-gatherers such as H. ergaster and H. erectus.

Although the genitalia are not visible in Figure 1.3, the larger individual on the left is clearly intended to represent an adult male. As we have seen, however, there is currently no certainty that sexual dimorphism in body size was this pronounced in the australopithecines. If indeed these creatures were markedly sexually dimorphic and polygynous, then the males in particular may also have possessed striking cutaneous secondary sexual adornments, such as capes and crests of hair, or fleshy facial elaborations, as these are often present in males of extant anthropoid species which have polygynous mating systems (Dixson, Dixson, and Anderson 2005). The smaller female has a protruding breast, with an areola area surrounding the nipple, as in H. sapiens. Again, inclusion of this detail owes something to artistic license. Breast enlargement due to fat deposition and the visually prominent pigmented areola area surrounding the nipple may have arisen much later in hominid evolution. As we shall see, in Chapter 7, fat deposition occurs at puberty in the breasts, buttocks, and thighs of women, and sex differences

Craneo Mono Dibujo
Paranthropus aethiopicus (the 'black skull'). Right: P. boisei ('Zinj',

in fat distribution have been affected both by natural selection and sexual selection during human evolution. These traits are much more likely to have emerged in early Homo (e.g. in H. ergaster and H. erec-tus) in association with changes in body shape, loss of hair, and other features connected with a hunter-gatherer existence in Africa.

Closely related to the genus Australopithecus, but currently regarded as occupying a distinct side-branch of the hominid evolutionary tree, are the robust australopithecines (genus Paranthropus) which occurred in Eastern and Southern Africa during the late Pliocene and early Pleistocene. They are known primarily from cranial and dental remains, and the term 'robust' relates to the powerful development of their jaws and large molar and premolar teeth. Their body sizes are thought to be similar to those of Australopithecus (Table 1.1).

Oldest of the three currently described species is Paranthropus aethiopicus (2.7-2.3 MYa) from Kenya and Ethiopia. Figure 1.4 shows the most complete skull recovered (the so-called 'black skull'), with its prominent sagittal crest (for attachment of the jaw muscles) surmounting a small cranium (brain size:

Left:

410 cc). Two other species have also been described: P. robustus (2.0-1.0 MYa, from South Africa) and P. boisei (2.2-1.2 MYa, from Ethiopia, Kenya, and Tanzania). Both of these species were alive at the same time as some of the earliest members of the genus Homo. From dental evidence, P. robustus is thought to have specialized in consuming a tough herbivorous diet. Such remains of the hand and foot skeletons that have been recovered indicate that it may have been more dextrous and more bipedal than A. afaren-sis (Susman 1988; 1994). P. boisei was a more extreme 'hyper-robust' form, with molar teeth four times the size of those of modern humans. When P. boisei was discovered, at the Olduvai Gorge in Tanzania in 1959, it was originally assigned to a separate genus

(Zinjanthropus) and its huge chewing teeth earned it the nickname 'nutcracker man' (Figure 1.4).

Figure 1.5 shows Grine's reconstruction of what a group of P. robustus might have looked like, as it foraged in the wooded grasslands of Southern Africa. An adult male Paranthropus standing upright is depicted as markedly larger than the females in the social group. The face of the male is more massive, and there is a suggestion of a beard. This is in accord with published accounts of pronounced sexual dimorphism and possible polygyny in the robust australopithecines. However, to counterbalance this assumption it should be kept in mind that very few fossils are known with any certainty to represent females of these apes. One female in the group is shown nursing her infant,

Figure 1.5 Grine's representation of a group of Paranthropus robustus, as it might have appeared in life, at Swartkrans in South Africa Source: Professor Fred Grine and the South African Journal of Science.

whilst next to her a second female is digging for tubers with a stick. Tool use of this kind is unconfirmed for the robust australopithecines, but is likely to have occurred. The hand is thought to have been adapted for a range of movements; In Figure 1.5, the female employs a 'power grip' to wield her digging stick, whilst in the foreground another member of the group is picking berries using a 'precision grip' of the thumb and index finger. Chimpanzees are known to use a variety of simple tools (McGrew 1992), and the occasional use of sticks as tools has also been documented in the gorilla and the orangutan. P. robustus is thought to have resembled the chimpanzee in body weight yet, at 515 cc, its brain was approximately 100 cc larger than that of a chimpanzee. It is generally agreed that Australopithecus and Paranthropus both had larger brains, relative to body mass, than is the case for the extant great apes (Martin 1983, 1990). Thus it is reasonable to infer that P. robustus might have used simple tools, although there is no fossil evidence of this. Not until the advent of H. habilis is there evidence of an association between hominid fossil remains and more durable (stone) tools.

The genus Homo is not thought to have arisen directly from any of the robust australopithecines described here. However, there are indications that Homo is closely related to Paranthropus (Strait, Grine, and Moniz 1997), so an as yet undiscovered stem form may be ancestral to the human genus. Both A. africanus and A. afarensis have also been proposed as possible human ancestors at various times, but further discoveries or reinterpretations of existing material will be required to resolve this question (Fleagle 1999).

Uncertainties concerning the precise origins of the genus Homo are linked to uncertainties about relationships between the earliest members of the genus, several species of which are known to have occurred in Africa at around 2 MYa. H. habilis lived in Southern and Eastern Africa, from approximately 2.3 to 1.6 MYa. The initial discoveries of these fossils were made at the Olduvai gorge in Tanzania during the 1960s, and were assigned by Louis Leakey and his colleagues to the genus Homo (Leakey, Tobias, and Napier 1964). The relatively small brain size (590-690 cc) of H. habilis, its ape-like limb proportions and resemblance to australopithecines have led to considerable debate about its taxonomic affinities

(Wood 1992; Walker and Shipman 1996). Recently, for example, it has been reported that H. habilis and H. erectus were sympatric in East Africa, approximately 1.55 MYa, making it unlikely that H. habilis represents a direct ancestor of modern humans (Spoor et al. 2007). Palaeontologists have found it difficult to determine the affinities of some fossils which may, or may not, belong to H. habilis. Oldowan tools (hammer stones and simple flakes) have been found associated with the fossilized remains of this species, hence its Latin name H. habilis, which means 'handy man'. It has smaller molar and premolar teeth than the australopithecines, and a more advanced foot anatomy, as well as a robust hand with curved, chimpanzee-like fingers and a large thumb.

The marked size differences exhibited by fossils of H. habilis have led to speculation that it might have been sexually dimorphic. However, it is unknown in many cases whether individual fossils belong to males or females, or even whether they represent members of different species. With so little evidence, speculation concerning the mating system of H. habilis is of little value. Smith (1984), for example, in discussing the evolutionary origins of human sexual behaviour and sperm competition, argued that H. habilis engaged in multi-partner mat-ings, and that sperm competition would have led to the evolution of large testes and a large penis in males of this species. At the time when he advanced these ideas, H. habilis was the major candidate for the earliest species of the genus Homo; thus Smith attempted to identify traits consistent with sperm competition in what was then thought to be the direct ancestor of H. sapiens. However, as we shall see in Chapters 3 and 4, the assumption that sperm competition has played a significant role in the evolution of the genus Homo is not supported by extensive comparative studies of the reproductive anatomy and behaviour of extant primates.

The realization that some of the fossils originally designated as H. habilis were too divergent to represent a single species led to the recognition that another species of early Homo existed in East Africa during the same time period. This was H. rudolfensis, named by Alexeev (1986) in honour of its discovery site at Lake Rudolf (now Lake Turkana), in Kenya. It is best known on the basis of the skull (KNM-ER 1470), described by Leakey

Figure 1.6 Two possible reconstructions of the KNM-ER 1470 skull (Homo rudolfensis). On the left, the face has a more vertical orientation, as is typical of members of the genus Homo (Leakey 1973). On the right, a more sloping, australopithecine facial morphology is shown (Walker and Shipman 1996). Author's drawings from photographs.

Figure 1.6 Two possible reconstructions of the KNM-ER 1470 skull (Homo rudolfensis). On the left, the face has a more vertical orientation, as is typical of members of the genus Homo (Leakey 1973). On the right, a more sloping, australopithecine facial morphology is shown (Walker and Shipman 1996). Author's drawings from photographs.

(1973), of a larger-brained (752 cc) hominid which lived approximately 1.9 MYa (Figure 1.6). Very little can be said concerning its post-cranial anatomy however, largely because of uncertainties about whether fossils currently assigned to H. habilis or Paranthropus might belong to H. rudolfensis.

It is important to reiterate that the taxonomic status of H. habilis and H. rudolfensis has been much debated by palaeontologists. The strong affinities shown by both these hominids with the australopithecines have led some authorities to recommend that they should not be included in the genus Homo (Wood and Collard 1999). However, retention of both taxa in the genus Homo is supported by cladistic analyses of hominoid craniofacial traits (González-José et al. 2008). On the other hand, it is interesting that Alan Walker, who has played a key role in reconstructing these fossils, believes that the face of KNM-ER 1470 was more projecting and australopithecine in its morphology than the reconstruction presented by Richard Leakey (both interpretations are shown in Figure 1.6). Thus, Walker and Shipman (1996) point out that '1470 might have a big braincase, but morphologically it was just an australopithecine. . . . Ignoring the cranial capacity, the overall shape of the specimen and that huge face grafted onto the braincase were undeniably australopithecine.'

Much more extensive fossilized remains of a third type of hominid, H. ergaster, have also been found in Africa, spanning the period between 1.9

and 1.5 MYa. By far the most complete specimen, and one of the most spectacular finds ever made in hominid palaeontology is the so-called 'Turkana (or Nariokotome) boy' (Figure 1.7). Eighty per cent of the skeleton of this individual, an immature male estimated to have been about 12 years old, was recovered from Nariokotome, to the west of Lake Turkana. As a result, a huge amount has been learned about the functional anatomy and the likely capacities of H. ergaster (Walker and Leakey 1993; Walker and Shipman 1996). Although not fully grown, it is likely that the Turkana boy would have reached 6 ft in height as an adult, much taller than any of the earlier hominids. The limb proportions were, indeed, similar to those of modern humans but more robust and with a longer shin bone; H. ergaster was probably well adapted for longdistance walking and running. The jaw was reduced in size, and the cheek teeth were smaller than in the australopithecines or H. habilis. The Turkana boy had a broad, flat face with a large, projecting nose, but the cranial vault was relatively small. Thus, at 800-900 cc the brain of H. ergaster was much smaller than in H. sapiens.

Figure 1.8 shows a reconstruction of what this young individual might have looked like in life. The overall proportions of the head, body, and limbs can be represented with greater confidence than in the australopithecine reconstructions described earlier. Features of surface morphology are always

Turkana Boy Skull

Figure 1.7 Skeleton of Homo ergaster based upon an immature male specimen (the 'Turkana' or 'Nariokotome boy'), dated at 1.6 MYa.

Source: Author's drawing, from photographs in Fleagle (1999) and Stringer and Andrews (2005).

Figure 1.7 Skeleton of Homo ergaster based upon an immature male specimen (the 'Turkana' or 'Nariokotome boy'), dated at 1.6 MYa.

Source: Author's drawing, from photographs in Fleagle (1999) and Stringer and Andrews (2005).

problematic, but some carefully considered deductions are included in this reconstruction. Thus, at least from the neck down, H. ergaster probably looked very human. It is surmised that by this stage of hominid evolution loss of body hair, increased sweat gland activity, and other adaptations for long-distance, bipedal locomotion would have been present. The skin was probably black, as befits an African hominid skilled at traversing open country and exposed to high levels of UV radiation. Studies of variation at the melanocortin receptor (MC1R) locus in extant human populations have also provided evidence for increased skin pigmentation, as an accompaniment to hair loss in human ancestors about 1.2 MYa (Rogers, Iltis and Wooding 2004).

One interesting detail included in Figure 1.8 is that the eyes of the Turkana boy are represented as having a prominent white sclera surrounding the dark iris and pupil. Comparative studies of the eyes of extant primates have shown that forms which live in more open, savannah conditions have eyes that are (horizontally) wider and (vertically) narrower. Humans belong to this group. However, the white sclera of the eye is an additional trait, highly developed in humans (Kobayashi and Kohshima 2001), but present also as an occasional anomaly in apes (Jane Goodall (1986), for example, records that one of her chimps at Gombe exhibited this trait). The white of the eye probably evolved in association with non-verbal communication, as subtle facets of facial communication often involve making, or breaking, eye contact. The white sclera is especially striking when the eye is viewed against the dark skin of the face.

H. ergaster, with its relatively small brain, is not thought to have used a spoken language, but its capacity for non-verbal (especially visual) communication was likely to have been highly developed in social and sexual contexts. Alan Walker expresses the view that the eyes of H. ergaster probably reflected 'that deadly unknowing I have seen in a lion's blank yellow eyes. He may have been our ancestor but there was no human consciousness within that human body. He was not one of us.' (Walker and Shipman 1996). However, in Chapter 7, it will be argued that many of the effects of sexual selection upon the evolution of human body shape, skin tone, secondary sexual traits and facial sex

Turkana Sex

Figure 1.8 Reconstruction of the 'Turkana boy' as he might have appeared in life.

Source: Author's drawings, based upon a reconstruction exhibited at The Museum of Man, San Diego, USA.

differences derive from forms such as H. ergaster. As regards non-verbal communication and patterns of mate choice, H. ergaster may have been very much 'one of us'.

H. ergaster was very closely related to another hom-inid, H. erectus, which is best known from sites far beyond Africa, and especially from Java and China. Some authorities consider that H. ergaster and H. erectus should be placed in the same species (Rightmire 1990). Originating in Africa, H. erectus spread to Asia between 1.8 and 1.5 MYa, where it survived until comparatively recently (some specimens from the Solo River in Java may be only 27,000 years old).

The skull of H. erectus had a long, low cranial vault, surmounted by a sagittal keel and with pronounced brow ridges above the eye sockets

Sagittal Keel

(Figure 1.9). The brain was relatively small in earlier specimens, but increased in size during the huge span of time that this species existed. Thus, cranial volumes ranging between 800 and 1250 cc have been recorded, reflecting effects of individual variability, and also a tendency for brain size to increase throughout the evolution of H. erectus (Figure 1.10). Extensive archaeological evidence indicates that H. erectus was an active hunter, and perhaps a scavenger, manufacturing (Acheulian) stone tools in order to butcher prey such as antelope, horses, and elephants. Whether this extraordinary hominid used fire is debatable (Balter 1995). It is, of course, probable that H. erectus was a gatherer as well as a hunter, relying heavily upon plants, and not just upon animal protein, for survival.

Figure 1.9 Lateral views of skulls attributed to Homo erectus. (A) The original skull cap, discovered at Trinil in Java, by Dubois in 1891. (B) The Sangiran 17 skull, from Java (dated at 700,000 years old). (C) The KNM-ER 3733 skull, from Koobi Fora in northern Kenya (circa 1.6 MYa). Pronounced differences between skulls (B) and (C) are interpreted by some authorities as evidence that they belong to separate species. Author's drawings, from photographs.

Figure 1.9 Lateral views of skulls attributed to Homo erectus. (A) The original skull cap, discovered at Trinil in Java, by Dubois in 1891. (B) The Sangiran 17 skull, from Java (dated at 700,000 years old). (C) The KNM-ER 3733 skull, from Koobi Fora in northern Kenya (circa 1.6 MYa). Pronounced differences between skulls (B) and (C) are interpreted by some authorities as evidence that they belong to separate species. Author's drawings, from photographs.

Fossils from Georgia (Dmanisi), including five skulls with cranial volumes ranging from 610775 cc and dated at approximately 1.7 million years, may also belong to H. erectus or H. ergaster. They have been assigned to a separate species, H. geor-gicus (Gabunia et al. 2000), although few authorities have followed this classification. Much more problematic is a diminutive fossil hominid from the Island of Flores in southeast Asia which has been mooted as a late surviving, pygmy descendent of H. erectus. A brief diversion from the mainstream of human evolution is justified here, to consider this recent discovery, as it has caused considerable controversy.

Only a single skull and partial skeleton of the Flores hominid has been described, as well as a second mandible and fragmentary postcranial remains from a number of other individuals (Brown et al. 2004; Morwood et al. 2004; Morwood and van Oost-erzee 2007). Known only from one location, the Liang Bua cave, the remains of this putative new hominid (H. floresiensis) are associated with stone tools; a hearth; and fossil remains of the Stegodon (pigmy elephant), Komodo dragon, and other species, probably eaten by the cave's occupants as recently as 18,000 years ago. However, claims that

H. floresiensis was responsible for these traces of technology and hunting activity are highly contentious. The very small brain of H. floresiensis (400 cc) is most unusual for such a recent hominid (Figure

I.10) and its size would normally be considered as incompatible with production of the artefacts recovered from Liang Bua. This has given rise to much discussion as to whether the fossils truly represent a new species of Homo, or whether they should be placed in a separate genus (Sundanthropus was the generic classification originally considered). More than one authority has provided evidence that the skull is morphologically abnormal, and presents features found in some modern human microcephalics (Weber, Czarnetzki and Pusch 2005; Martin et al. 2006a; 2006b; see also Richards 2006; Hershkovitz, Kornreich, and Laron 2007). Rebuttals of this hypothesis have occasioned a lively debate (Falk et al. 2005a; 2005b; 2006). Most recently, Obendorf, Oxnard, and Kefford (2008) have added another twist to these debates by suggesting that the Flores hominids were members of H. sapiens whose stunted growth was caused by chronic thyroid deficiency (cretinism).

As more evidence comes to light, controversies surrounding H. floresiensis and associated finds at Liang Bua may serve as cautionary reminders of how ill-advised it is to make far-reaching interpretations based upon limited or conflicting fossil evidence. Errors of this kind have occurred in the past. As an example, Dart (1957) incorrectly interpreted

Figure 1.10 Progressive Increases In brain size during homlnld evolution. Cranial capacities of Individual fossil homlnld specimens have been plotted against time, beginning at almost 3.5 MYa. The arrow indicates the anomalous position of Homo floresiensis, given its recent date and small cranial capacity.

Source: After Martin et al. (2006b), and based upon data in Stanyon et al. (1993).

Figure 1.10 Progressive Increases In brain size during homlnld evolution. Cranial capacities of Individual fossil homlnld specimens have been plotted against time, beginning at almost 3.5 MYa. The arrow indicates the anomalous position of Homo floresiensis, given its recent date and small cranial capacity.

Source: After Martin et al. (2006b), and based upon data in Stanyon et al. (1993).

material from the limestone caves where Australopithecus was discovered as evidence that it had an 'osteodontokeratic culture', and used tools made of bone, teeth, or horn to kill and prepare prey for cooking. One of the discoverers of H. floresiensis, Mike Morwood, says that he himself let his mind drift into the past to try to capture the emotions and feelings of these tiny humans who had once been alive, sheltering in Liang Bua, bringing in hunted game and vegetables, or bundles of firewood to be carefully used for cooking, warmth and light. (Morwood and van Oosterzee 2007: p. 110).

However, critical reasoning indicates that, equipped with a brain smaller than that of most australop-ithecines, it is not at all likely that H. floresiensis could have made the complex stone tools at Liang Bua, or that it had mastered the use of fire, or the ability to cook. The hypothesis that its small brain was somehow 're-wired' to be exceptionally efficient for its size begs the question of why this should have happened only on the tiny island of Flores and why other hominids have failed to achieve such neurological adaptations, especially as to do so would have conveyed huge physiological advantages.

Alternative and much less problematic explanations exist which may explain the co-occurrence of H. floresiensis with stone tools and other evidences of human activity at Liang Bua. There is ample evidence that modern H. sapiens occurred on the island of Flores and would have overlapped for an extensive period of time with H. floresiensis. Thus, a more parsimonious interpretation of the finds at Liang Bua might be that the artefacts and animal remains are due to the activities of more advanced hominids whose remains may yet come to light in those areas of the cave that have still to be excavated.

Let us now return from this brief foray into a side channel of hominid evolution, and rejoin the mainstream of evidence provided by H. erectus. The variability of fossils discovered in China, Java, and Africa has led authorities to recognize that they may represent more than one species. In China, for example, fossils recovered from a cave at Zhoukoudian (near Beijing) and at several other sites are sometimes ascribed to H. pekinen-sis, but are acknowledged as sharing many features with H. erectus fossils from Java and Africa. It is generally argued that the sexes were probably less dimorphic in body size than in earlier hominids such as the australopithecines. Thus, in Table 1.1, the estimated ratio of adult male and female body weights for H. erectus is 1.2, and is the same as for modern humans. However, many uncertainties remain regarding the degree of sexual dimorphism in various populations currently assigned to H. erectus. Spoor et al. (2007) have described an unusually small H. erectus skull (endocranial capacity 691 cc) from Ileret, in Kenya. They argue that the large variations in size displayed by H. erectus may indicate that it was much more sexually dimorphic than modern humans. However, it is impossible on the basis of current fossil evidence to resolve this question, or to decide whether the evolution of such sexual dimorphism was due to inter-male competition within polygynous or multi-male/multi-female mating systems.

The fossil record of human evolution in Africa during the period spanning 1.2 million and 600,000 years ago is relatively poor. However, skulls of a large-brained (1225-1325 cc), and strongly built hominid species have been described from three sites (Kabwe, in Zambia; Saldanha in South Africa, and Bodo, in Ethiopia) and these are sometimes classified as H. rhodesiensis. H. rhodesiensis closely resembles another hominid, H. heidelbergensis, which has been described on the basis of finds at multiple sites throughout Europe, dated at between 600,000 and 250,000 years ago (Rightmire 1998). The original specimen (a jaw) was discovered in 1907 at Mauer, near Heidelberg in Germany. Still older fossils of a possible precursor of H. heidelber-gensis have been found at Gran Dolina in northern Spain. These remains, of multiple individuals and of stone tools, are estimated to be at least 780,000 years old, and were placed in a separate species

(H. antecessor) by their discoverers (Bermudez de Castro et al. 1997). Most recently, the remains of a mandible, dated at 1.2-1.1 million years, have been discovered at Sima del Elefante close to the site at Gran Dolina. It seems likely that H. antecessor, or its forerunners, were present in Southern Europe very early in the Pleistocene (Carbonell et al. 2008).

H. heidelbergensis and the closely related forms from Africa and northern Spain occupy a pivotal role in discussions of the origins of modern humans and of Neanderthal man. H. heidelber-gensis was a heavily built hominid, with robust limbs and a large brain. Many features of its skull align it very closely with H. neanderthalensis (Figure 1.11), and, indeed, it is thought to have given rise to the Neanderthals in Europe. Neanderthals were a shorter, stockier human species, distinct from H. sapiens, and well-adapted to life in colder conditions, although they also inhabited warmer climates in Eastern and Southern Europe, Central Asia, and the Middle East from approximately 200,000 to 30,000 years ago. A superb reconstruction of the complete Neanderthal skeleton was undertaken at the American Museum of Natural History by Sawyer and Maley (2005). Comparing this skeleton side-by-side with a modern human strikingly emphasizes the many differences. Their skulls display distinctive traits, including large brow ridges, a low forehead, receding chin, and a very large projecting nasal region. Their brains (ranging from 1200 to 1740 cc) were, in absolute terms, larger than those of H. sapiens, but their body size was also greater and probably exceeded 80 kg in some cases. These must have been very muscular and physically formidable humans, and the adult males were significantly larger than the females (Figure 1.12). The Neanderthals had mastered the use of fire, and they made distinctive (Mousterian) stone tools and also fashioned wooden spears and other implements (Stringer and Gamble 1993). A tangible hallmark of their humanity bequeathed to us across the millennia is the evidence that they sometimes buried their dead, a circumstance which has facilitated the preservation of their fossilized remains.

Much more is known about the Neanderthals than about their contemporaries in Africa. Both

Neanderthals and modern humans are documented to about 100,000 years ago in the Middle East, although they never occurred together. Curiously, the stone tools used by H. sapiens were essentially Mousterian initially, only becoming distinctive about 40,000 years ago. However, it is now clear that modern H. sapiens arose in Africa, quite separately from the Neanderthals but probably from common stock, consisting either of H. heidelbergensis (Right-mire 1998) or of H. ergaster (Klein 1999), depending upon which phylogeny is adopted to account for the timing and spread of hominid species during the Pleistocene (see Figure 1.13 for alternative schemata).

The earliest fossil evidence of anatomically modern H. sapiens has been found in Africa (in Ethiopia, Sudan, and South Africa) and it is likely that modern humans originated there more than 195,000 years ago. It is impossible to give exact dates because times are gradually pushed back as more fossils are discovered and accurately dated. The modern human skull has a distinctive high forehead, brain size is large (1000-2000 cc, average 1350 cc), and the superciliary (brow) ridges above the eyes are much reduced but, when present, they are largest in adult males. The face is reduced in size, and the jaw is slender, but with a projecting chin which, again, is larger in the male sex (Figures 1.11 and 1.12). In 2003, White et al. reported in the journal Nature their discoveries of hominid crania that are morphologically intermediate between those of archaic and modern H. sapiens. Dated at between 160,000 and 154,000 years, these fossils from the middle Awash Valley of Ethiopia are believed to represent 'the probable immediate ancestors of anatomically modern humans' (White et al. 2003). Subsequent work on dating of anatomically modern human remains at Omo Kibish, in Ethiopia, indicates that they are of a still more ancient origin, and may be 195,000 years old.

Les Pigme Omo Sexiel
Figure 1.12 Reconstructions of (left) Homo neanderthalensis, as compared to (right) modern Homo sapiens. Source: After Tudge (2000).
Sexual Dimorphism Humans

The African origin of modern humans is also borne out by a number of genetic studies, of mitochondrial and nuclear DNA, and of Y chromosome mutations in human populations across the world (Ke et al. 2001; Ramachandran et al. 2005; Liu et al. 2006). The greatest genetic diversity exists in African populations, and it is thought that genetic 'bottlenecks' occurred as small founder populations of humans emigrated from

Africa, eastwards into Asia and northwards into Europe. Indeed, recent studies by Manica et al. (2007) have demonstrated a remarkable agreement between loss of genetic diversity and reductions in phenotypic diversity (skull morphology) in 105 human populations worldwide. The most likely area of origin for modern H. sapiens, based upon both genetic and phenotypic studies, includes Southern, and Central/Western Africa,

Spreading The Sapiens

Figure 1.13 Two alternative phylogenies which have been applied to hominid evolution during the Pleistocene. (A) Rightmire classifies African and Asian Homo erectus as a single species. In Africa, this gave rise to H. heidelbergensis, and subsequently to H. neanderthalensis (in Europe) and H. sapiens (in Africa). (B) Klein's scheme places H. ergaster in Africa, at 1.8 MYa, and spreading to Asia, where it gave rise to H. erectus. H. ergaster also reached Europe, where it gave rise to H. neanderthalensis, while in Africa it was also the forerunner of H. sapiens. Source: Redrawn from Boyd and Silk (2000).

as shown in Figure 1.14. Studies of the genetic diversity of Helicobacter pylori, a bacterium which occurs in the stomach of more than 50 per cent of all humans, also confirm the likely African origin of H. sapiens. There is increasing loss of genetic diversity of Helicobacter pylori sampled from human populations at progressive distances from Africa (Linz et al. 2007).

Modern research thus provides strong support for the out of Africa hypothesis of modern human origins. This has largely replaced the older multiregional model of human evolution. This model posited that H. sapiens arose in different parts of the world, from founder populations of H. erectus with, perhaps, some degree of genetic exchange between such populations (Thorne and Wolpoff 1981). Coon (1962), in his Origin of Races, for example, attempted to derive the Australian aborigines from founder populations of H. erectus in southeast Asia. He did not regard them as springing from the same genetic stock as geographically distant populations of H. sapiens, such as those in Europe. Indeed Coon considered 'that the Australian aborigines are still in the act of sloughing off some of the genetic traits which distinguish H. erectus from H. sapiens.' Only a short step would separate such misguided views from the promotion of racial superiority as being pre-ordained by biology.

In reality, extant populations of Australian aborigines, in common with all other human populations, represent the result of emigration of anatomically modern H. sapiens from Africa. The ancestors of modern aborigines reached Australia at least 60,00050,000 years ago. As well as moving eastwards to occupy Asia, modern humans also populated Europe, beginning at about 45,000-40,000 years ago (Figure 1.15). In the process, they would have encountered the resident populations of Neanderthals. However, there is no evidence that H. sapiens and H. neanderthalensis interbred extensively. Analyses of ancient DNA extracted from Neanderthal fossils do not support the view that any significant

Figure 1.14 The African origin of Homo sapiens, and decreases in (A) phenotypic diversity (skull morphology) and (B) genetic diversity In extant human populations as indicated by darker shading at progressively greater distances from Africa. The bold line on each map encloses the probable area of origin of anatomically modern humans in Africa. Source: After Manica et al. (2007).

Figure 1.14 The African origin of Homo sapiens, and decreases in (A) phenotypic diversity (skull morphology) and (B) genetic diversity In extant human populations as indicated by darker shading at progressively greater distances from Africa. The bold line on each map encloses the probable area of origin of anatomically modern humans in Africa. Source: After Manica et al. (2007).

exchange of genetic material took place between these two species (Krings et al. 1997; Stringer 2002). Rather, it seems probable that modern humans 'out-competed' Neanderthals (in ecological terms), so that they gradually withdrew into less favoured areas and dwindled in numbers. The Neanderthals are thought to have become extinct at around 30,000 years ago, although small numbers of them may have persisted until more recent periods (Mellars 2004).

Figure 1.15 Modern humans originated in Africa more than 195,000 years ago, and by 100,000 years ago they had begun to colonize the rest of the world. Likely routes and dates of the earliest migrations are represented on the map. Source: Based upon information in Stringer and Andrews (2005).

The evolution of human culture is beyond the scope of this book, but it is necessary to address the question of the likely cultural capacities of the earliest humans, in Africa more than 195,000 years ago. Could they speak? Did they possess the same degree of abstract reasoning, and aesthetic sensitivities as ourselves? Clearly, any insights concerning these questions may also affect judgements about the sexual lives, mating systems, and patterns of mate choice in early H. sapiens.

A great flowering of late Palaeolithic artistic activity is best documented for the period beginning 40,000 years ago, among those humans whose ancestors had emigrated from Africa and entered Europe. To them we owe a legacy of skillfully painted cave art, finely made tools, and even sculpture, including the enigmatic 'Venus' figurines, which will be discussed in Chapter 7. The question of whether these cultural attainments were the result of gradual, or sudden, change in Europe has occasioned much debate (Klein 2000; McBrearty and Brooks 2000; d'Errico et al. 2005; Mellars 2006). However, recent discoveries of shell beads made by H. sapiens in Africa at between 82,000-75,000 years ago make it clear that humans were creating symbolically significant objects, and were culturally advanced well before our species had entered Europe. At the Blombos cave, in South Africa, perforated beads, made from the shells of small marine snails, have been excavated from strata which are 75,000 years old (d'Errico et al. 2005). The presence of traces of red ochre on the shells may indicate that the wearers of the beads also adorned themselves with this pigment. Strikingly similar beads made using a species belonging to the same genus of snail (Nassarius) as at Blombos have also been excavated from the Grotte des Pigeons in Morocco. These beads are older (82,000 years) than at Blombos, but also bear traces of red ochre. Together with finds at other African and southeast Asian sites, they indicate that personal ornaments were made, and possibly were distributed over large distances 'at least 40 millennia before the appearance of similar cultural manifestations in Europe' (Bouzouggar et al. 2007).

The position taken here is that anatomically modern H. sapiens, originating in Africa at some period before 195,000 years ago, was also physiologically modern, as regards the structure and functions of the brain, as well as the reproductive and other organ systems. The origins of language are unknown, but Cavalli-Sforza et al. (1988) have shown that the degree of genetic relatedness between various modern human populations is paralleled to a remarkable degree by linguistic similarities. Thus, languages derive ultimately from common roots and from the original, African populations of H. sapiens. Cultural evolution would not have progressed at the same pace, or in the same way in the various populations which remained in Africa, or those which emigrated, and were subject to genetic bottlenecks and diverse environmental pressures in other parts of the world (Figure 1.15).

Culture did not begin with the origin of H. sapiens, and earlier species such as H. heidelbergensis and H. erectus would likely have possessed homologues of human culture, albeit at less complex levels. The gradual enlargement of the brain which has occurred during hominid evolution (Figure 1.10) may have been affected by both natural selection and sexual selection (Miller 2000). There is no reason to deny that some form of 'proto-language' might have existed in the common ancestor (e.g. H. heidelbergensis) of the Neanderthals and modern humans. On that assumption, both H. neanderthalen-sis and H. sapiens would have possessed language capacities, which diverged during long periods of widely separated evolution in Europe and Africa, respectively.

The intellectual skills used by the first H. sapiens, in Africa, to track and hunt prey, to forage, make tools, defend themselves against predators, and to communicate, survive, and reproduce within social groups were formidable. Although our modern technology is obviously much more advanced, fundamentally, as regards sexual behaviour we share many traits with our remote ancestors. The origins of some of these sexual traits, as determinants of the mating system, patterns of copulatory behaviour and mate choice are explored in the next eight chapters.

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  • Sophia
    When a man erectus why is it that the penis bends?
    4 months ago

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