How Is the Cephalic Index Calculated and Why Does It Matter?
Cephalic index is given as the percentage of breadth to length in any of the skulls. The index is determined by measuring the diameters of the skull. The distance between the glabella (the midpoint between the brows) and the most projecting point on the back side of the head is used to calculate the skull length. The breadth of the skull is given as the distance between the most projecting points at the sides of head, generally a little above and behind the ears.
Range of Cephalic index
The cephalic index is given as the breadth, which is multiplied by 100 divided by the length. An index of below 75 means that the skull is narrow and long when seen from the top; such types of skulls are known as dolichocephalic and they are typical of Australian aborigines and the native southern Africans. An index of ranging 75 - 80 means that the skull is approximately oval; such skulls are known as mesaticephalic and are typical of the Chinese and Europeans. A skull, which holds an index of about 80 is short and broad, and is known as brachycephalic; such skulls are quite common among the Andaman Islanders and Mongolians.
Historic Use in Anthropology
Early Anthropology
In the early twentieth century, anthropologists used to calculate the cephalic index (cephalic index calculator) to categorise the human population. Now, it is primarily used to describe the individuals' appearances and for estimating the fetuses age for obstetrical and legal reasons.
Anders Retzius (1796–1860), a Swedish professor of anatomy, invented the cephalic map, which was first used in physical anthropology to classify ancient human remains found in Europe. This theory became more closely associated with the racial anthropology development in both 19th and early 20th centuries, when the prehistorians attempted to use ancient remains to model population movements in terms of the racial categories. Also, the Carleton S. Coon used the index in the 1960s.
Indices
Cephalic indices can be grouped as in the below table:
Technically, the measured factors can be defined as the maximum width of the bones, which surround the head above the supramastoid crest (it means, behind the cheekbones), and the maximum length from the very easily noticed part of the glabella (between the eyebrows) to the very easily noticed point at the back side part of the head.
Controversy
Giuseppe Sergi challenged the cephalic index's utility, claiming that cranial morphology was a better way to model racial ancestry. In addition, Franz Boas analysed the children of immigrants to the United States between 1910 and 1912, finding that the children's cephalic index differed significantly from that of their parents, suggesting that local environmental factors had a major impact on cephalic head shape growth.
Boas also argued that the cephalic index was useless for defining race and mapping ancestral populations if craniofacial features were too malleable in a single generation. Scholars like Earnest A. Hooton continued to argue that both heredity and environment were involved. But, Boas did not himself claim it was completely plastic.
In 2002, Jantz and Sparks re-evaluated some of Boas' original data using modern statistical techniques, concluding that the shape of the head had a "relatively large genetic component." The new study, according to Columbia University's Ralph Holloway, raises concerns about whether differences in skull shape have "adaptive significance" and whether "normalising selection may be at work on the trait, where both hyper brachycephaly and hyper dolichocephaly are at a small disadvantage in terms of selection."
Modern Use in Animal Breeding
The cephalic index can be used in the categorisation of animals, especially in the breeds of cats and dogs.
Brachycephalic Animals
Relatively, a brachycephalic skull is short and broad (typically having the breadth at least 80% of the length). Some dog breeds, such as the pug, are known as "Extreme Brachycephalic." Due to the health issues brachycephaly is regarded as torture breeding, often, as it leads to the Brachycephalic airway obstructive syndrome.
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List of Brachycephalic Dogs
American Bulldog
Affenpinscher
Boxer
Boston Terrier
Brussels Griffon
List of Brachycephalic Cats
British Shorthair
An Exotic Shorthair
Exotic Shorthair
List of Brachycephalic Pigs
Middle White
List of Brachycephalic Rabbits
Lionhead rabbit
Jersey Wooly
Lop rabbit
Mesaticephalic Animals
Mesocephalic Labrador Retriever
A mesaticephalic skull consists of intermediate width and length. These mesaticephalic skulls are not markedly dolichocephalic and brachycephalic. When dealing with animals, especially dogs, the more common and widely used term is "mesaticephalic," which refers to the ratio of the head to the nasal cavity. This group is exemplified by the breeds mentioned below.
List of Mesaticephalic Canines
Alaskan Malamute
African Wild Dog
List of Mesaticephalic Cats
Note: Almost all the felines are known to be mesaticephalic
American Bobtail
American Shorthair
FAQs on Cephalic Index Explained: Biology, Meaning & Applications
1. What is the cephalic index?
The cephalic index (CI), also known as the cranial index, is an anthropometric measurement used to describe and classify the shape of the head. It is calculated as the ratio of the maximum width of the skull (biparietal diameter) to its maximum length (occipitofrontal diameter), multiplied by 100. This numerical value allows for a standardised comparison of head shapes across individuals and populations.
2. How is the cephalic index calculated?
The formula to calculate the cephalic index is straightforward. You measure the maximum width of the head (from side to side) and the maximum length (from front to back) and apply the following formula:
Cephalic Index (CI) = (Maximum Head Width / Maximum Head Length) × 100
The measurements are typically taken using spreading calipers in physical anthropology or derived from imaging techniques like CT scans in a clinical setting.
3. What are the different classifications of head shapes based on the cephalic index?
Based on the calculated index, head shapes are generally categorised into three main types. These classifications help in understanding the relative proportions of the skull:
Dolichocephalic: A cephalic index below 75.0, indicating a long and narrow head shape.
Mesocephalic (or Mesaticephalic): A cephalic index between 75.0 and 79.9, indicating a medium or average-proportioned head.
Brachycephalic: A cephalic index of 80.0 and above, indicating a short and broad head shape.
4. What is the importance of the cephalic index in modern science?
While its historical use in racial classification is now considered unscientific and obsolete, the cephalic index remains important in several modern fields. Its primary importance lies in providing objective data for:
Clinical Medicine: Paediatricians use it to monitor infant head growth and diagnose conditions like craniosynostosis (premature fusion of skull sutures) or plagiocephaly (flattening of the head).
Forensic Anthropology: It serves as one of many tools to help build a biological profile of unidentified skeletal remains, offering clues about ancestry and individual features.
Evolutionary Biology: It is used to study and compare cranial shape variations across different hominid species and modern human populations to understand evolutionary trends.
5. How is the cephalic index used in medicine, particularly during pregnancy?
In medicine, the cephalic index is a valuable tool, especially in obstetrics and paediatrics. During pregnancy, fetal biometry using ultrasound includes measuring the head's biparietal diameter (BPD) and occipitofrontal diameter (OFD) to calculate the cephalic index. This helps in:
Assessing normal fetal cranial development.
Detecting potential abnormalities in skull shape like dolichocephaly or brachycephaly in utero.
Ensuring that other measurements, like head circumference, are interpreted correctly, as an unusual head shape can affect these readings.
6. What role does the cephalic index play in forensic anthropology?
In forensic anthropology, the cephalic index is one of several cranial measurements used to help identify human skeletal remains. While not definitive on its own, it contributes to building a biological profile of an individual. Its main application is to provide an initial estimation of ancestry, as some populations have a higher prevalence of certain head shapes (e.g., brachycephalic or dolichocephalic). It can help narrow down possibilities when combined with other skeletal features and forensic evidence.
7. Can the cephalic index of an individual change over time?
Yes, the cephalic index is most malleable during early life. The skull of an infant is soft and pliable, and its shape can be influenced by various factors. The index can change significantly from birth through the first few years of life due to:
Rapid brain growth.
Sleeping position (e.g., prolonged back-sleeping can lead to a broader, flatter head, increasing the cephalic index).
Medical conditions affecting skull growth.
Once the cranial sutures fuse and the skull fully hardens in late adolescence and early adulthood, the cephalic index becomes fixed and does not naturally change.
8. Why do different human populations exhibit variations in their average cephalic index?
Variations in the average cephalic index across different human populations are a result of the complex interplay between genetic and environmental factors.
Genetic Heritage: Genes are fundamental in directing the overall growth pattern of the skull. Over long evolutionary timescales, genetic drift and natural selection within geographically distinct populations have led to a higher frequency of certain head shapes.
Environmental and Cultural Influences: Factors like climate have been proposed as having an adaptive influence. More directly, cultural practices, especially infant-care techniques like cradle-boarding or consistent sleeping postures, can systematically influence head shape within a population, affecting the average cephalic index.
9. Is there a difference between the cephalic index and the cranial index?
Yes, there is a technical difference, although the terms are often used interchangeably. The cephalic index is measured on a living individual, where soft tissues like skin and muscle are present. The cranial index is measured on a dry skull, without any soft tissue. Because of the absence of soft tissue, the cranial index measurements are slightly different from the cephalic index of the same individual when they were alive. However, the calculation formula and classifications remain the same for both.
