Argumentum ad hominem

As I noted in an earlier post, this blog was partly named as a misspelt pun on the ad hominem argument. Argumentum ad hominem (Latin: "argument to the man") involves attacking the character or circumstances of one's opponent in order to undermine them, instead of addressing the substance of their argument. Ad hominem arguments are generally regarded as fallacious, since they do not address the opponent’s argument itself.

This argument comes in the following forms:

The tactic is to portray the opponent as a bad or immoral person, and conclude based on this, that their argument should not be accepted, e.g.

Ann says that anthropological research needs more funding. This is coming from a woman who divorced her husband.

Involves suggesting that the person making the argument is so doing out of self interest, e.g.

She's an anthropologist. Of course, she's going to say that evolution is true.

Tu quoque (Latin: "you too")
This is commonly heard in political debates. Also referred to as the "hypocrisy argument" or the “you too fallacy”, it involves showing that the opponent's arguments or criticisms apply or have applied to them, e.g.

You said Neandertals and modern humans interbreed but only last year you said that they didn't.

Poisoning the well
Is a pre-emptive attack meant to discredit one's opponent before they even make their argument, e.g.

Darwinists have been preaching the evolution lie for years. I suspect that tonight's debate won't be any different.

Guilt by association
Is the view that an individual shares the qualities of others based on irrelevant associations, e.g.

Craniometrics was used in the early twenthieth century to promote eugenics. Anthropologists who carry out craniometric analyses are like Nazis.

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Race: an anthropological perspective

Forensic anthropologists often have to establish a biological profile of an individual based on their skeletal remains. This involves establishing probable age, sex, stature and race. The last category seems to be at odds with the consensus view in modern biology, which views the race concept to be biologically meaningless. Since this is the case, then why do forensic anthropologists insist on determining race?

Alice Brues defined race as "a division of a species which differs from other divisions by the frequency with which certain hereditary traits appear among its members." This definition of race, like most others, is rather equivocal, in that it does not tell us how much variance in the frequency of traits necessitates the creation of a new race. If we take this definition at face value then according to craniometric and genetic data an incalculable number of races exist.

In 1972, R.C. Lewontin reported that, for genes at a single locus, most genetic variation existed within populations, rather than between them. For most biologists this put the nail in the coffin for the race concept. In a re-examination of Lewontin's findings, the Cambridge statistician A.W.F. Edwards, noted that our ability to correctly classify populations is due to the correlations among different loci. By focusing on multiple loci the between population differences increase dramatically.

As way of an analogy, imagine we asked a stranger the following question via internet: "Which colour do you prefer less: orange or brown?" Previous surveys have showed that there is a slightly greater tendency for women to rate orange as their least favourite colour, while men have a slightly greater tendency to dislike brown. However, there is a very high amount of overlap. We would have a tough time trying to predict sex based on the results of this single question. However, if we ask say thirty questions instead of one, we would be able to predict sex with a much higher degree of certainty based on the responses as a whole. In a similar manner, we could not confidently determine race of an individual based on one or two cranial measurements. However, the likelihood of a positive determination increases significantly when we include more measurements.

Craniometrics has been shown to correctly classify individuals into a few broadly defined racial categories, as well as many more geographically localised categories. The ability of forensic anthropologists to accurately classify individuals into predefined groups does not substantiate the biological race concept. Just because we can determine a skeleton to be of Irish, Western European, Northwestern European or European ancestry does not mean that such ancestral groups exist in any meaningful biological sense. However, such information is useful for homicide investigators who are interested in whittling down their list of possible missing persons.

So how are we to understand race? Human variation is probably best understood in terms of both temporal and geographic distances. Cranial variation correlates strongly with geography; meaning that the further apart the populations are geographically, the more dissimilar they are phenotypically. Conversely, neighbouring populations show greater phenotypic similarities, spurring anthropologist Frank Livingstone to write in 1962 "there are no races, only clines”. The relationship between phenotypic variation and geography is likely due to both isolation by distance (there is greater gene flow between neighbouring populations) and the many founder effects that occurred in the course of human history. The longer groups remain isolated the more dissimilar their genotypes. Since most racial categories are defined by geographic regions, it should not come as a surprise that there is a correlation between race and place of ancestry.

Race is a crude sociocultural construct based on the underlying reality of biological variation. In this regard it is similar to other cultural phenomena, which help us understand our past. For example, much can be ascertained about ancestry and human migration by studying languages. In this regard, race has proved to be a useful concept in the fields of medicine and law enforcement. As long as law enforcement continue to use racially defined categories, forensic anthropologists will similarly follow suit.

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A little human with very big feet

hobbit feet
A recent conference and a handful of publications on the diminutive hominin Homo floresiensis (a.k.a. the “hobbit”) have brought to light the difficulty of placing this fossil neatly into the human family tree. A recent study of the 18,000 year old fossil’s feet has raised many intriguing questions. The difficulty in situating this species is that it has an complex mix of both ancestral and derived traits.

The pelvis and legs all clearly demonstrate that
Homo floresiensis was bipedal. However, the hominin’s feet are unusually long compared to the leg. This combination of a long foot and a relatively short leg is seen in some apes but not in hominins. The navicular acts like the keystone in the arch of the human foot and is elevated from the ground except in people who have fallen arches. In Homo floresiensis this bone has a well developed tuberosity meaning that it was in contact with the ground, like in other flat-footed great apes and early hominins. The overall shape of the foot means that this hominin would not have been able to run long distances very efficiently — a distinguishing feature of later Homo. While the hominin had a short chimp-like big toe, it was not opposable like in other hominins. The long, curved lateral toes resemble a chimpanzee’s, rather than those of a human which are short and straight. The distal first metatarsal is squared off like in modern humans but this feature is not found in other early hominins, such as Australopithecus afarensis, Paranthropus robustus or the early Homo remains from the Georgian site of Dmanisi.

It is generally thought that
Homo erectus was the first hominin to leave Africa, soon after their first appearance in the archaeological record around 1.9 million years ago. Based solely on archaeological data Homo erectus seems like the best ancestor for Homo floresiensis. Homo erectus has been show to be a highly variable species. Homo floresiensis could represent a descendent of Homo erectus that adapted to island life through a dramatic decrease in size. While some of the plesiomorphic traits of Homo floresiensis may be explained through evolutionary reversals, it is unlikely to account for all of the primitive traits in the skeleton as a whole. It has been suggested that the ancestor of Homo floresiensis was not Homo erectus but rather a more primitive hominin. The 1.8 million year old skeletal Homo remains from Dmanisi are relatively primitive. At first glance, this species might seem like a good ancestral candidate for Homo floresiensis. However, unlike Homo floresiensis, the Dmanisi specimens have quite modern limb proportions. Homo habilis has also been forwarded as a possible candidate although there is little archaeological evidence to suggest that that species ever left Africa. Until further evidence comes along, the jury is out on this miniature human.

Reference cited
Jungers et al. The foot of Homo floresiensis. Nature 459, 81-84 (7 May 2009) | doi:10.1038/nature07989

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Is craniometry scientific?

Craniometry is the measurement of the bones of the skull. The technique is primarily used to determine ancestry, population distances and sex. It differs greatly from the psuedoscientific fields of phrenology and physiognomy, although in the general populace the distinction is not so clear. The book Postmodernism and Race has the following definition: "Craniometry is the measurement of human skulls as an indication of intelligence", while a recent blog article on craniometry states that it "claims to be able to predict the intelligence and nature of human being." Craniometry says nothing about intelligence or human nature.

Craniometric studies were, to a large degree, racially motivated in the early decades of the twentieth century, with anthropologists trying to validate their preconceived racial categories. In 1912, Franz Boas published a study challenging the prevailing notion that certain cranial measurements were under ironclad genetic control. He studied the head form of some 13,000 European immigrants and their American-born children. He found significant differences in the shape of the heads between parents and their children, which he interpreted as evidence for cranial plasticity. In other words, environment, not genetics, shapes cranial morphology. During the subsequent decades, Boas' results came to be largely accepted by the anthropological community, with students of the Boasian school disregarding craniometric studies as an ill-fated enterprise. For many years, anthropologists steered clear of craniometry, instead focusing their expertise in other less stigmatised areas of physical anthropology such as palaeopathology.

Quite recently papers by Sparks
et al (2002) and Gravlee et al (2003) have re-examined Boas' original data. However, those expecting the final word on cranial plasticity were to be disappointed. The anthropologist Milford Wolpoff is quoted as saying in 1975 "The data do not speak for themselves. I have been in rooms with data and listened very carefully. They never said a word." This is particularly true of these two papers, which use the very same data to come to divergent conclusion. While Gravlee et al believe Boas to be essential correct, Sparks et al came down firmly on the other side. The real answer, I believe, is to be found between the lines.

Boas did, in fact, find a statistically significant environmental effect in his study but this begs the question of whether it is a meaningful effect. Sparks suggests that while the effect is real, it only constitutes a tiny proportion of variation. In fact, considering the size of Boas' sample (~13,000) it is almost impossible not to find statistically significant results; biology is, after all, intrinsically variable. It may be the case that Boas played up the importance of the environmental effects as a reaction to the racial thinking that was prevalent at that time.

Perhaps, the biggest problem with Boas' methodology was his reliance on only a handful of measurements and particularly the use of the cephalic index (ratio of head breadth to head length). Anders Retzius introduced the cephalic index as way of classifying skulls based on their overall shape. He defined three main categories: dolichocephalic (long headed), brachycephalic (broad headed) and mesocephalic (intermediate headed).

Most modern biological anthropologists are of the opinion that the use of a couple of measurements to describe a multi-complex structure such as the skull is absurd. Today, biological anthropologist will take dozens of measurements of the skull. W. W. Howells, who measured thousands of skulls from all over the world, had the following to say about the cephalc index: "When Anders Retzius, a century and half ago, invented the cranial index, he gave us an answer for which there was no question." Even Boas himself wrote the following in 1940: "Measurements should always have a biological significance. As soon as they lose their significance they lose also their descriptive value."

Craniometry is used today in biological anthropology as a means of determining the relationships of peoples through their phenotype. A phenotype is the visible manifestation of a genotype. Since there is rarely a one to one relationship between the genotype and phenotype we must first demonstrate that the phenotype is an accurate reflection of the genotype. If this is not the case craniometry would be no more scientific than phrenology. Narrow-sense heritability is the proportion of phenotypic variation that arises from only the additive genetic differences among individuals and is expressed as h
2 = VA/VP. Heribtaility is measured on a scale of 0 (no heritable variation) to 1 (all phenotypic variation is due to additive genetic effects). The average cranial h2 has been estimated at around 0.55 (Relethford 1994; Devor 1987). A heritability greater than 0.5 indicates that most phenotypic variation is the examined traits are attributable to genetic factors. Thus the proportionality of genotypic to phenotypic variance is a reasonable assumption. The true litmus test of any hypothesis is its predictive power. Craniometric data is used with surprising accuracy by forensic anthropologists to determine likely ancestry of unknown individual and by palaeoanthropologists to determine our relationship to other hominins. The modern scientific practice of craniometry distinguishes itself from psuedosciences like phrenology and physiognomy in that it is based on sound biological theory, it is testable, it is predictive and objective.

References cited
Boas F (1912) Changes in the bodily form of descendants of immigrants. American Anthropologist 14: 530-562.

Sparks CS, Jantz RL (2002) A reassessment of human cranial plasticity: Boas revisited. Proc. Natl. Acad. Sci. USA 99: 14636-14639.

Gravlee CC, Bernard HR, Leonard WR (2003) Heredity, Environment, and Cranial Form: A Reanalysis of Boas's Immigrant Data. American Anthropologist.

Devor EJ (1987) Transmission of human craniofacial dimensions. J Craniofac Genet Dev Biol 7: 95-106.

Relethford JH (1994) Craniometric variation among modern human populations. Am J Phys Anthropol 95: 53-62.

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Ad Hominin. What's in a name?

Until quite recently humans and their ancestors were referred to as hominids. This was a reflection of taxonomy of the time: the family Hominidae consisted of humans, while the family Pongidae consisted of orangutans, chimpanzees, gorillas and bonobos. However, molecular studies showed humans, chimpanzees and bonobos to be more closely related than previously thought. The current consensus taxonomy for the family Hominidae consists of the following subfamilies: Ponginae (orangutans), Gorillinae (gorillas) and Homininae (chimpanzees, bonobos, humans). Strictly speaking chimps, bonobos and humans are all hominids. However, we still need a way to talk about ourselves and our ancestors. The Homininae subfamily is divided into two tribes: Panini (chimpanzee, bonobo) and Hominini (humans). Thus, in recent years there has been a growing trend of referring to humans and their ancestors as hominins.The Latin prefix ad means "towards", so ad hominin can be translated as "towards humankind". Many of you will undoubtedly notice the allusion to argumentum ad hominem - a type of argument where one attacks the character of the opponent rather than their arguments. This pun is intended and reflects my interest in critical thinking and logic.Many people lack the cognitive toolkit to critically examine such psuedoscientific claims as homeopathy, psychokinesis or acupuncture. As a physical anthropologist I am well aware that evolution is not impervious to wild misconceptions. It is my hope to give people the tools and knowledge necessary to recognise fallacious arguments and critically examine extraordinary claims.

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