Forensic Biology
Sex Determination From Skeletal Remains

Sex Determination From Skeletal Remains

Sex or gender is one of the important characteristics that helps in determining the identity of an individual. The terms sex and gender are not to be confused in this context. Gender is a sociocultural construct, and sex is a biological trait.

There are various types of methods that can be employed in sex determination of the deceased, such as general appearance of the person, secondary sexual characteristics, gonadal examination, footprint ratio, nuclear sexing and examination of bones and odontology. Among these methods except the bones and odontology all other characteristics can be used in determination of sex in both live and dead person. 

When a non-decomposed body is found on the crime scene, it is easy to estimate the sex of the deceased by examination of secondary sexual characteristics and gonadal characteristics. But there are times when the forensic scientists only get the skeletal remains of the deceased.

There the sex estimation is quite difficult since all skeletons appears same. However, at present the process is not so difficult as many methods have been developed for the same and those methods have been proved reliable by the standard authorities. 

However, the only disadvantage of using bones for sex estimation is that it cannot be determined with full certainty in individuals who have not reached puberty as the sexual characteristics do not begin to manifest by that time.

In an adult individual the sex determination from the bones is like a revolution in forensic identification. Here the Sex estimation is based on the premise that male and female skeletal morphology differs in size and shape, as the skeleton shows sexual diamorphism. Practitioners uses two types of methods for estimating sex- Non metric methods and Metric methods.

Non-Metric Method

Non-Metric methods are the one which uses visual examination of the morphology of the skeleton or bones. There are some specific bones which have high degrees of sexual diamorphism and are usually considered for the purpose. The most commonly used bones are- skull, mandibles, spinal cord, thorax, pelvis and femur.

1. Skeleton

The parameters which are used to determine the sex of an individual through skeleton involves- the weight of the skeleton, length of long bones and the texture of bone.

Male skeleton is usually heavier than that of female. In males it weighs upto 4.5 kg while in female it is estimated to be about 3 kg. 

The shafts of long bones of females are smoother than that of the males. The articular surfaces ends are smaller than that of the males. Prominent muscular ridges, depressions and processes are present in males while in females all these are less prominent. 

2. Skull

Skull is the hard bony covering enclosing the brain inside it. It’s structure show sexual diamorphism in the size, capacity and texture. 

The male skull is bigger, heavier and more rugged than the female skull. The cranial capacity of male skull is almost 10% more than the female skull. The specific regions of skull which show high sexual diamorphism are:

  • Frontonasal Angulation- It is fully distinct in males whereas in females it is not well marked.
  • Frontal Sinuses- It is well developed in males but for females it is less developed.
  • Glabella, Zygomatic Arch, Occipital Protuberance, etc.- The attachment of these regions with the muscles is more pronounced in males than females. 
  • Facial Bones- The facial bones in females are less massive and delicate in texture than in males.
  • Orbital Opening- The orbital opening in males is bigger and rectangular whereas in females it is smaller and rounded. 

3. Mandibles 

In females the lower jaw is not as massive as in males. The ramus is less broad and the angle region is everted as compared to males. The chin bone or the symphysis menti is rounded or pointed in females whereas in males it is square. 

4. Thorax 

The rib cage is wider and short in females, while in males it is longer and narrow. The ribs of females are oblique and the curvature is more pronounced whereas in males they have less oblique and less pronounced curvature.

The male’s sternum body is bigger and more than twice the length of manubrium but for females the sternum body is shorter and less than twice the length of manubrium. 

The upper border of the sternum is levelled with the lower part of the second thoracic vertebra in males. In females it is the third thoracic vertebra.

5. Spinal Column

The breadth of the first cervical vertebra is 72 mm in females and 83 mm in males.

6. Femur Bone

The femur or thigh bone is the longest bone of the human skeleton. 

In males the femur head is large, the acetabulum is wide and the articular surface forms more than two-thirds of a sphere. While in females, the femur head is smaller, the acetabulum is narrower than males and the articular surface forms less than two-thirds of a sphere. 

The angle between the femur neck and shaft is a right angle in females and an obtuse angle in males. 

7. Pelvis 

It is also called hip bone and the most reliable bone for accurate sex determination, that is 95% accuracy. The reason being instead the female skeleton is more gracile and smaller in overall size pelvic traits collectively contribute to a wider pelvis as it relates to parturition, or child-bearing.

  • The inlet of the pelvis is broad and shallow in females while in males it is narrow and deep.
  • The ilium is expanded in females and the walls are splayed.
  • The suprapubic arch is wide, U-shaped and forms a right angle in females. In males the suprapubic arch is narrow, V-shaped and forms an angle of 70 degrees. 
  • In females the obturator foramen is triangular and in males it is ovoid. 
  • The greater sciatic notch is wide, shallow and almost forms a right angle in females.
  • Inverted ischial tuberosities are present in males whereas in females the tuberosities are everted.
  • The preauricular sulcus is narrow and shallow in males. Whereas in females it is broad and deep.
  • The sacrum is wide and short, having five segments in females. In males, it is long and narrow having five or more segments. 

Metric Method

These methods include equations based on skeletal dimensions. It is favoured because of the objectivity associated with osteometric data but is only possible if equations from geographically and temporally appropriate reference samples are available. 

The usual bones considered are the long bones, pubis and sacrum.

1. Femur

In males the vertical diameter of the femoral head is more than 47 mm while in females it is less than 45 mm. 

2. Humerus 

The vertical diameter of the humeral head is less than 41.5 mm in females and in males it is more than 45.5 mm. 

3. Sacrum

The sacral index for females is 116 and 112 for males. It is calculated as:

Sacral Index = breadth of base of sacrum *100 / anterior length of sacrum 

4. Pubis

From this bone ischiopubic index is calculated which is calculated as:

Ischiopubic Index = pubic length * 100 / ischium length

For females the index is 91-115 and for males it is 73-94.

Conclusion

The skeleton is the bony framework of every human individual. Though all skeletons appear similar, each one is unique. In fact they vary according to sex of an individual. The reason for this varies between genetics, hormonal variation, culture and environment. An adult skeleton can easily reveal the sex of an individual, but it is not possible in individuals who have not reached puberty. 

In adults the sex determination can be conducted reliably through non-metric or visual examinations and metric or bone measurements. The degree of sex determination from skeletal remains have been estimated by Krogman which states: the accuracy of sex determination is– long bones(80%)<skull(90%)<pelvis(95%)<skull and pelvis(98%)<entire skeleton(100%). 

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