Lecture notes, October 21, 2003, K. Denning
zip down to Visions of our Ancestors
A FEW POINTS OF REVIEW
basic skeletal biology –
age indicators - juvenile – epiphyseal closure, dent eruption
- adult -- wear and tear (pubic symphysis, auricular surface, cranial suture closure, sternal rib ends, dental wear, arthritis etc.)
chronic disease shows in the bones (TB, leprosy, syphilis), as do use patterns and also intentional modification. General stress also shows in teeth and bones (enamel hypoplasia, Harris lines)
trace element and stable isotope analysis for diet and nutrition
main sex indicators in the adult - pelvis and skull
key stuff in evolution (see earlier handout)
adaptation – an adaptive trait increases the chances that an organism will survive to reproduce, and that its offspring will survive to reproduce. Note! traits that are adaptive in one environment may not be in another (remember all those creatures we looked at last week.) N.g. much of evolution is about being in the right place at the right time, i.e. having necessary traits to survive a huge change in climate.
Natural selection needs three principles:
a) variation: every species consists of individuals, who vary
b) heritability: offspring inherit traits from their parents
c) differential reproductive success: better-adapted individuals produce more offspring than the worse-adapted
Therefore, the individuals best adapted to their environment survive and reproduce more successfully, thus shifting the overall characteristics of the species. Note! Natural selection acts on the phenotype, not directly on the genotype. (i.e. recessive or unexpressed genes are unaffected)
Primate characteristics:
a) mammals (hair/fur, warm-blooded, give birth to live young, mammary glands, young are dependent upon adults and learn from them
b) additional features:
- skeletal features adapted for arboreal existence in some cases – e.g. suspensory shoulder with clavicle, flexible forelimbs (rotating, two bones, radius and ulna)
- omnivores generally, with unspecialized back teeth and specialized front teeth;
- larger brain, less smell, more sight, more learning ability
- stereoscopic vision (eyes in front, good depth perception)
- prehensile (grasping) hands and feet, opposable thumbs – precision grip
- reproductive system – pendulous penis, two nipples, uterus designed for one fetus
- infant-rearing – infants are dependent on mother and group for a long period, are not mature for several years
- usually social, though some are solitary
- most are diurnal (active in daylight), though a few are nocturnal or crepuscular
Juvenile primates need: a warm, social relationship with a mother or caregiver (Harlow experiment referred to in text -- for more details, see here: http://psychclassics.yorku.ca/Harlow/love.htm), and a chance to play (this is learning), or they become socially dysfunctional
sexual dimorphism (diff size and appearance in m/f) varies - very pronounced in some, less so in others (related to social organization)
When we’re studying fossils
We have to contend with infrequent fossilization, fragmentary remains and the challenges of taphonomy (the changes that occur to organisms or objects after being buried or deposited), including scattering of remains, exposure to the elements, etc. Have to consider why things are found together (deliberate deposition, accidental coincidence, etc.)
Human evolution
First Primates: Oligocene, around 34 mya (what were they like initially? little insectivores and fruit eaters, probably nocturnal and arboreal - improving eyesight and declining smell, good grasping hands)
First OW monkeys and apes: Miocene anthropoids, starting 24 mya.
Middle and Late Miocene apes (hominoids) -- Kenyapithecus in Africa. Sivapithecus in SW and W Asia (more like orang), and Dryopithecus in Europe (more like chimp)
BIG FOSSIL GAP in Africa, 13.5 to 5 mya. Not much found. Unfortunate! (we're working on it)
TYPES OF EVIDENCE: Fossils but also "molecular clock": which takes DNA from modern species, looks at how different they are, and estimates time of divergence
First hominids: between 8 and 5 mya
Key Trends in Hominid Evolution: Bipedalism, expansion of brain (cranial capacity), modification of female pelvis, reduction of teeth, face, and jaws, extended period of infant and child dependence, apparent increased reliance on meat, emergence of tool use etc.
Bipedalism - changes in knee, foot (esp big toe), pelvis, spine curvature
Early hominids in general had 3 major adaptive problems - being large mammals, terrestrial primates, living in an open, savanna environment (Fagan 39)
Bipedalism might have been an advantage because (Ember 175) increased ability to see predators and prey, free hands for carrying food, tool use, long distance traveling more efficient.
Cranial capacity: Australos - 380 to 550 cc, vs. early Homo 630-640, vs. Homo sapiens sapiens (us!), usually 1300+ cc N.B. this does vary with body size, and the simple size of the brain alone does not mean greater intelligence within a species. Bigger and more complex brains - linked to stone tool making? around 2.5 mya (Oldowan tool industry),
Maybe teeth got smaller because of a change away from tough grains and grasses as food, and because people started to cook?
Emergence of division of labour - rather helpless infants requiring nursing can cause restriction of activity in the mother. Hence the theory about females gathering and males hunting. n.b. in more recent hunter-gatherer societies, females often participate in hunting smaller animals and in communal hunts, and both genders gather and scavene.
Australo Species: new ones being discovered all the time! Most hominid fossils found in Great Rift Valley of East Africa, and also in South Africa. (Ethiopian, Tanzania, Kenya, and S. Africa)
Gracile: A. africanus (Taung child) was an early discovery, A. afarensis (Lucy) was a big find in the 70s (40% of skeleton!), clearly bipedal
Robust australos: (Paranthropus/A. boisei, robustus, aethiopicus)
More recent finds: A. anamensis, A. garhi, etc.
Special note: the debates over species names and relative positioning are heated. Esp. Johanson and Leakey camps.
Homo species: bigger brains, reduced molars and premolars
2.5 mya onwards: Homo habilis (Olduvai)
Earliest tools seem 2.5 mya but dispute over who made them (A? H?) -- Oldowan tradition, chopper tools and flakes, pretty basic but very useful for cutting plants and also meat (n.b. we only have stone tools -- and what else might they have used?)
1.7 to 1.5 mya: Homo erectus emerges - significant because these are the first found out of Africa, in Europe and Asia (some have reclassified the African ones as H. ergaster). Early-discovered specimens: 'Java Man', 'Peking Man'. Bigger brain (895-1040 cc), different brain proportions, and larger overall body size (like us). Prominent, projecting bone. Very dense thigh bones. Developed Acheulean tool tradition from 1.5 mya. Clear evidence of big game consumption (hunting? scavenging?) Potential use of fire 1.4 mya, definite use and control of fire for cooking 500 000 BP in China. Also apparent use of basic structures. Language? Could be. Looks like their brains were up to it, at a basic level.
Archaic Homo sapiens, H. sapiens neanderthalensis.
Considerable continuity between H. erectus and archaic H. sapiens in some place....hard to draw the line. (still, decreasing jaw, face, back teeth, cranial capacity)
Neandertal: Original find, 1856, was amazingly controversial and very influential in later perceptions of the Neandertal people. (First reconstruction based upon an older male suffering from severe arthritis.) Walked completely upright, looked much like modern humans, actually had bigger brains than us, had sloping foreheads, large brow ridges, large jaws, minimal chins. Lived throughout Europe, SW Asia, and Central Asia.
Anatomically modern Homo sapiens – which is what we are – emerged in the Pleistocene epoch, specifically around 150 000- 200 000 bp.
More on H. sapiens next week.
Overall:
How do we decide what is one species and what is another? This is tough : ) and we have 'lumpers and splitters' in the field. Ember 181 has a good description of the process. It's easier when we have a reasonable number of specimens, but very hard when we only have one or two.
When looking at reconstructions (drawings, sculptures, and film), consider:
What is fact?
What is representation?
Consider the following illustrations:
From top left: A. anamensis, A. afarensis, A. africanus, H. habilis, H. erectus, H.s.neanderthalensis. (With apologies to the website I swiped these from.)
Which aspects of these illustrations are based on known facts of palaeoanthropology/archaeology? Which are extrapolated? Which are completely invented?
Consider the skulls (left to right: A. afarensis, A. africanus, H. erectus, H. sapiens sapiens)
- fairly well known facts - basic facial structure, cranial capacity, tooth size etc. (though remember that the skulls are themselves often reconstructed from fragmentary and damaged fossils)
- facial reconstruction in bioarchaeology and forensics is based on some good modern data about tissue depths on the face, etc. (e.g. see http://www.shef.ac.uk/assem/1/mpefig01.html )
- but! eye colour, skin colour, amount of hair, hair colour, hair style -- all are extrapolated.
- also of interest in reconstruction drawings - facial expressions and gender
When we consider reconstruction images (drawings, film) of hominids 'in their natural habitats', we see even more areas of extrapolation and invention.
Examine the images below (selected from works by Stephanie Moser and Melanie Wiber):
Archaeology scholars S. Moser and M. Wiber have examined these kinds of reconstruction illustrations and have noticed several key themes.
- there are 'icons' which tend to be present in these images, signifying primitivity and a separation from us: spears, clubs, skulls, long hair, etc.
- the relative positioning and activities of males, females, and children say a lot about perceived gender relationships in the past -- and in the present. (males tend to be the very 'Man the Hunter', are the ones with tools, weapons, are looking the most inventive, and are located centrally in the image)
In Films
there is even more richness in the representations, which says as much about us as it does about the people we are representing.
e.g. Many 'prehistoric' films: Clan of the Cave Bear, Quest for Fire, One Million Years B.C., etc.
In film, one can usually see the icons that are present in still illustrations, but there is also a lot of extrapolation about:
- subsistence - only men hunt, women gather (rather a caricature - not taking into account scavenging etc.)
- interpersonal relationships and group organization - very patriarchal, authoritarian leadership, frequent squabbles over dominance
- intergroup relationships - constant conflict between groups
- language use, spirituality, and reasoning capacity
- constant struggle against a hostile environment
- motion patterns
Some of this extrapolation is reasonably based on information about anatomy etc., but much is rather tenuous.
So, what is this all about?
1) Specific point for this theme: Our understanding of human evolution has been steadily changing ever since palaeoanthropological investigation started. (Generalization for the course: Scientific understandings change significantly over time. What we believed was true even just five years ago may not be our best guess today.)
2) Specific point for this theme: Our understanding of human evolution has been shaped by cultural preconceptions of what makes us human: intelligence, bipedalism, hunting, language, etc. And it's influenced by essentially political notions of: what is culturally superior, which people should rule the earth, and what relationships between genders, within families, and between groups should be like... not to mention notions of what our relationship to the natural environment should be like. (Generalization for the course: Scientific knowledge is culturally constructed as well as discovered. Metaphors and narratives influence scientific understanding.)
3) Specific point for this theme: visual reconstructions both of hominid species and of human evolutionary history are influenced by more than just the actual fossils, and include submerged assumptions about the nature of evolution, our position on Earth, and our destiny. (Generalization for the course: a scientific reconstruction always has zones of subjectivity, and the way that subjectivity is handled depends on preconceptions which are often unstated, but which the perceptive reader must try to find.)
4) Even though we know a great deal about human evolution, we don't have very many definite answers. Part of the reason why not is that we haven't agreed on what kind of evidence is the strongest (e.g. fossils or DNA), or on what methods are the best ways of studying evidence. There are always several different ways of seeing the data -- and we can't always agree on which way is the best. (Generalization for the course: About most complex questions, scientists disagree, and disagree legitimately. Therefore, one should be a critical reader who always checks for more than one point of view, lest one miss this reality and think that one scientist is definitely right.)
So.... are palaeoanthropologists just making everything up? Do scientists really know anything about human evolution or is it all just stories?
No, it's not all just stories. We have a lot of facts. But science -- any and every kind of science -- is never perfectly objective. Popular representations of science are less objective still, because they make scientific information accessible by taking facts, and placing them within a story that people care about (our human history), and putting a face on them. This doesn't mean that scientific research, popular articles or museum presentations are without value, but it does mean that they include built-in biases that readers need to be aware of.
Palaeoanthropology provides just one example of subjectivity in archaeology. We will talk about others as the year continues.
Why is the visual representation of evolution so important?
First of all, because images are generally more influential in our minds than words, and because once we have a picture in our mind, it's difficult to "update it" or replace it with another one unless we consciously focus on it. So the classic image of the Neanderthal (hairy, brutish, etc.) sticks in our minds and influences how we think about Neanderthals.
Second of all, paintings or sculptured reconstructions of human ancestors include all kinds of biases and assumptions that we don't necessarily have evidence for. For example, human ancestors have most often been portrayed using conventions about maleness, skin colour, hairiness, and certain behaviours, that we just don't have evidence for. Those assumptions are based on our ideas about what 'primitive' and 'civilized' people look like. (See Moser and Berman.) But because the image is powerful, we can tend to believe that it is true.
(So why draw reconstructions at all? Because they're so fascinating, and because they can help us think about what it is that we're looking at. But we need to approach them with skepticism, and to throw them away when they don't fit the data anymore.)
Third, representations of the path of evolution really shape our understanding of how evolution takes place. Often in the past, representations of human evolution were linear, suggesting that species simply transformed from A. afarensis to A.africanus to H.habilis to H. erectus, etc.... But it wasn't like this. We are not the inevitable product of a linear progression from 'lower' forms to 'higher' forms of life. We are one surviving twig of a diverse family tree, and in the past, more than one twig was alive at a time. Different hominid species coexisted. Gould demonstrates that if we visualize evolution as a tree with lots of dead twigs -- the model of diversification and decimation -- then we can understand that chance has played a big part in our presence here on earth. And this has huge implications for how we see ourselves, and for our philosophy.
So will we ever know the real truth about human origins?
That depends on what you mean by "real truth", and how you believe we can find it, and how you think we can recognize it if we're looking at it.
This answer is not being evasive -- it's reflecting the heart of the scientific endeavour. Scientists don't always agree on how to know things for sure. (For understanding human evolution, should we place our faith in DNA analysis, or in fossil morphology? See Maienschein article.) But does this failure to agree on what knowledge is most worthwhile, and how to get it, mean that scientists don't know anything? No. Of course they know things. This just makes understanding science a little messy, and it means that one can't take anything for granted.
Naturally, any scientific inquiry about the origins of something is impossible to finish, because there is always the possibility of finding a new fossil that tells us that everything we've assumed so far is wrong. This is in the nature of the inquiry.
So if we can't find the answer for sure, why do we bother looking? Why are scientists spending all of this time trying to understand human origins? Why do people go to look at this stuff in museums, watch television shows and buy popular books about human evolution? Why is it important?
Human beings are fascinated by themselves, and they're fascinated by stories about themselves. Why else would all religions include stories about how human beings were created? Science can answer a similar need: a need to understand where we came from, what we really are, and where we're going. The philosophical implications can be major, as well -- as demonstrated by the Scopes trial and the general shock in the 1800s and 1900s over the Darwinian notion that human beings share an ancestor with apes. This rocked people's world, and their religious faith.
If we know where we came from, and the forces that have shaped us into what we are, we might have a better idea of how to live in the present. And if we know what ISN'T true about ourselves and our evolution, then we can know how to respond to people who justify political positions in the present by arguing, for example, that different races are evolutionarily inferior or superior, or that having a gender means that you're 'naturally' programmed for certain social roles and not others.... etc. So this isn't a strictly academic question.
And finally, no page about human evolution is complete without a link -- just for fun -- to a couple of Sasquatch sites: http://www.ncf.carleton.ca/~bz050/HomePage.bf.html, and http://www.phobe.com/yeti/ As usual, keep an open mind, but don't believe everything you read. : ) Consider the narratives which are implicit in Bigfoot theories!
Some good refs:
Tattersall, Ian. 2000. “Once We Were Not Alone” in Scientific American , January 2000. Vol. 282 no. 1 pp 56-62.
Andrews, Peter and Christopher Stringer. 1993. “The Primates’ Progress” from The Book of Life, edited by Stephen Jay Gould. pp 219-251.
Maienschein, Jane. 1997. “The One and the Many: Epistemological Reflections on the Modern Human Origins Debates” in Conceptual Issues in Modern Human Origins Research. Geoffrey Clark and Catherine Willermet, editors. pp 413-422.
Landau, Misia. 1991. “Prologue”, from her book Narratives of Human Evolution. pp 1-16.
Landau, Misia. 1991. “Preface”, “Epilogue: New Stories of Human Evolution” from her book Narratives of Human Evolution. pp. ix-xii, 175-185
Lewin, Roger. 1987. “Bones of Contention” pp 13-29. “The Storytellers” pp 30-46. “Man’s Place in Nature” pp 301-319 from his book Bones of Contention: Controversies in the Search for Human Origins.
Harré, Rom, Jens Brockmeier, Peter Mühlhäusler. 1999. “Environmental Narratives” in their book Greenspeak: A Study of Environmental Discourse. pp 69-89. COURSE PACK. OPTIONAL
Gould, Stephen Jay. 1989. “The Iconography of an Expectation” from his book Wonderful Life: The Burgess Shale and the Nature of History. pp 23-52.
Berman, Judith. 1999. “Bad Hair Days in the Palaeolithic: Modern (Re)Constructions of the Cave Man” in American Anthropologist vol. 101 no. 2, pp 288-304.
Moser, Stephanie. 1998. “Popular Presentations” from her book Ancestral Images: The Iconography of Human Origins. pp 146-167.