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paleoanthropology, genetics and evolution

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  • Cranial features and race

    Sun, 2011-11-27 21:51 -- John Hawks
    Synopsis: 
    A primer on assigning forensic race to crania based on their morphology

    Individuals whose ancestry derives mostly from different parts of the world sometimes have different cranial features. Forensic anthropologists have studied these differences for many years, finding some that are especially useful for distinguishing ancestry. In American legal contexts, ancestry is usually at issue as a way of determining the racial affinity of unidentified skeletal remains. Hence, the forensic anthropologist usually tries to make a determination as to whether a skull has features that indicate African, European, Asian or Native American ancestry.

    Cranial features are not perfect indicators of ancestry: Forensic anthropologists using multiple features claim at best 85% accuracy in their assessment of racial ancestry. When we know less about the context of a skull, we will be less and less accurate.

    Here are some traits that vary between skulls with different race backgrounds. Most of them are on the face or palate.

    • Shape of the eye orbits, viewed from the front. Africans tend to a more rectangular shape, East Asians more circular, Europeans tend to have an ``aviator glasses'' shape.
    • Nasal sill: Europeans tend to have a pronounced angulation dividing the nasal floor from the anterior surface of the maxilla; Africans tend to lack a sharp angulation, Asians tend to be intermediate.
    • Nasal bridge: Africans tend to have an arching, ``Quonset hut'' shape, Europeans tend to have high nasal bones with a peaked angle, Asians tend to have low nasal bones with a slight angulation.
    • Nasal aperture: Africans tend to have wide nasal apertures, Europeans narrow.
    • Subnasal prognathism: Africans tend to have maxillae that project more anteriorly (prognathic) below the nose, Europeans tend to be less projecting.
    • Zygomatic form: Asians tend to have anteriorly projecting cheekbones. The border of the frontal process (lateral to the orbit) faces forward. In Europeans and Africans, these face more laterally and the zygomatic recedes more posteriorly.

    What to do: This station includes several casts representing skulls of different ancestries, along with one ``mystery skull''. Examine the features that vary by ancestry in this skull, comparing it with the others. Can you assess the racial origin of the mystery skull?

    Study terms: 
    race
    nasal sill
    nasal bridge
    nasal aperture
    subnasal prognathism
    zygomatic
    orbit
    Tags: 
    race
    Anthropology 105
    laboratory
    explainer
    anatomy

  • Determining sex from the cranium

    Tue, 2011-11-15 07:51 -- John Hawks
    Synopsis: 
    A lab station discussing nonmetric features of the skull in relation to sex determination.

    The cranium has a very distinctive shape, but there is variation between people in the sizes and forms of different parts of it. Some features that vary between individuals in their size or shape are called nonmetric features, because they can be observed, but are not normally measured in centimeters or any other scale.

    Forensic anthropologists use features of the skull to help determine the sex of skeletal remains. Males tend to have larger, more robust skulls --- meaning that their crania are heavier, thicker, and have more distinct muscle attachments. Obviously, with a cast of a skull we cannot judge the overall weight, but size is still relevant.

    The following features can be helpful in determining sex.

    Superciliary arches
    Thickenings in the frontal bone underlying the medial part of the brow. Rarely in humans, the thickened ridge of the brow extends completely to the side of the skull, forming a supraorbital torus. Males tend to have more pronounced superciliary arches, females often have none at all.
    Temporal lines
    These are the lines of attachment of the temporalis muscles, on the sides of the skull arching from the sides of the frontal bone and back across the parietal bones. These are often more marked in males than in females.
    Orbits
    The eye sockets are called the orbits. The lower border of the orbit can differ subtly in form between males and females. Males tend to have a blunter, more rounded surface here, females a sharper border.
    Nuchal lines
    These are attachments for the neck muscles on the occipital bone at the rear of the skull. The most obvious is generally the superior nuchal line, which may have a large swelling or bump at the center, called the external occipital protuberance. In human males, the markings for these muscles tend to be more pronounced than in females.
    Mastoid process
    The mastoid process is part of the temporal bone that juts beneath the skull behind the ear. This may be larger or smaller in different people. Apes do not have a human-like mastoid process. The area behind their ears is swelled up with air chambers, called pneumatization. In human males, this tends to be larger and more projecting, in females smaller.

    What to do: Examine the crania here. Which do you think are males? Females? Are there some that seem to be difficult to classify?

    Take the time to draw a male and female skull from the side, denoting the features that can help you distinguish sex.

    Study terms: 
    nuchal lines
    external occipital protuberance
    mastoid process
    superciliary arches
    supraorbital torus
    temporal lines
    orbit
    Tags: 
    Anthropology 105
    laboratory
    explainer
    anatomy

  • Bones of the cranium from the front

    Sun, 2011-08-21 20:09 -- John Hawks
    Synopsis: 
    A description of the bones of the skull visible from the front and above.

    The cranium includes all the bones of the head. Altogether, there are 26 cranial bones plus the mandible. Except for the mandible, these bones mostly are fused together so that they do not move. The joints between most of the cranial bones are borders where the bones knit together, called sutures. The sutures are places where the bones articulate, or contact, each other.

    On one of the skulls available, find each of the following bones:

    Frontal
    The bone of the forehead, above the eye sockets, or orbits.
    Parietal
    The two bones (left and right) of the top and sides of the vault.
    Temporal
    The lower sides (left and right) of the vault, including the ear opening, or external acoustic porus.
    Sphenoid
    Just anterior to the temporal bones, the sphenoid stretches through the skull from left to right.
    Maxillary
    The largest bones (left and right) of the face.
    Zygomatic
    The cheek bones (left and right).
    Nasal
    These bones, left and right, form the bridge of the nose.
    Mandible
    The bone of the lower jaw.

    The remaining bones of the skull can be harder to find, and this lab doesn't require you to learn them in detail. Six of them are the tiny bones of the middle ear on both sides. The ethmoid and left and right lacrimal bones are most visible on the medial (inner) surface of the eye orbits. The vomer and left and right inferior conchae are inside the nasal aperture. The larger bones listed above will be the most important for comparing humans with each other and other primates.

    Cranium with bones labeled in anterior and lateral view
    Study questions: 

    The frontal bone articulates with 12 other cranial bones. Three of these are the ethmoid and left and right lacrimal bones. Can you find the other nine?

    Study terms: 
    frontal
    parietal
    temporal
    sphenoid
    maxillary
    zygomatic
    nasal
    mandible
    external acoustic porus
    orbit
    vault
    articulate
    suture
    Tags: 
    teaching
    explainer
    laboratory

  • Bones and features of the skull

    Sun, 2011-08-21 19:49 -- John Hawks
    Synopsis: 
    Overview of the laboratory on bones and features of the skull.

    Goals

    • Learn about the major bones of the face and cranial vault, including the frontal, left and right parietal, left and right temporal, occipital, left and right maxillary, left and right zygomatic, and the mandible.
    • Examine some nonmetric features of the skull, including the supraciliary arch, mastoid process, foramen magnum, orbits.
    • Learn basic anatomical terms, such as superior and inferior.
    • Learn the method of seriation, and consider ways that the cranium varies between males and females.
    Study terms: 
    frontal
    occipital
    parietal
    temporal
    maxillary
    zygomatic
    mandible
    superior
    inferior
    supraciliary arch
    mastoid process
    foramen magnum
    orbit
    Tags: 
    teaching
    explainer
    laboratory
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