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[ Average Sexual Differences between Males & Females - How do human cultures accentuate these differences to look sexier? ]
[ Feature
Overall body
morphology
Overall skeletal
morphology
Skull
Differences ]
- Males larger, more robust, more angular features
- Females smaller, more gracile, larger percentage of body fat (why?); rounder features, more paedomorphic (retain more juvenile-like
characters in the adult stage). Juvenile traits invoke strong parental feelings, which is a mammalian characteristic. Check out Mickey
Mouse, Disney humans, such as Cinderella, or even the evolution of Garfield or Opus. Cartoonists soon learn how to make their characters
cuter and more appealing, i.e., draw them with large eyes & large heads, as in a child.
- Humans are sexually active year-round; females have a menstrual cycle with hidden ovulation; for this reason, humans have a number of
“permanent” sexual characters
- Males have a larger, more robust skeleton, bone & muscle mass greater, so tuberosities etc. of bones more prominent; cranium 10% larger.
Guess what the best predictor of brain size is for mammals: ___________________________
- Females more gracile (slender); with an adequate sample size, knowledge of culture, & personal experience, sexing bones can be done with
confidence, but characters between the sexes overlap too much for 100% predictability. Humans have low sexual dimorphism.
- Males more robust: larger braincase, external occipital protuberance present, mastoid process large, forehead greater slope, muscle
attachment lines more marked, supraorbital ridges more prominent, orbital margins dull, chin squared
- Females more gracile: superior orbital margin sharp, forehead bulging/more vertical, supraorbital ridges lacking or subdued; muscle
attachment lines slight
Muscle Mass &
Blood
- Males tend to have a larger muscle mass & also more blood than females (1.5 gallons versus 0.875 gallons on average), which one would
expect because men are bigger bodied, but their erythrocyte density is also higher—each cubic centimeter contains 4.6-6.2 million
erythrocytes, compared to 4.2-5.4 million in females
Eyes
- Males larger
- Females higher proportion of white, tear ducts appear to be more reactive
Why do humans have “whites around their eyes?” White-colored sclera surrounding the iris is a unique human trait.
Nose
- Males larger
- Females more paedomorphic (smaller nose; upturned nose; flatter nose bridge)
Cheeks
Round cheeks are uniquely human. Baby cheeks produce a parental response, so smooth cheeks are associated with intense love, and cheeks
are symbolically the gentlest part of the body. Females are more paedomorphic so they tend to have rounder cheeks.
Hair
- Males have coarser, longer, darker hair, so hair thicker & bushier on chest, arms, eyebrows, etc.; the beard is obvious signal of sexual
maturity and enhances the “maleness” of the face; after age 30 hair becomes noticeable on pinna; Male pattern baldness another sign of
judging age/reproductive fitness; hair also functions to retain body odor & pheromones; pubic hair is a signal of sexual maturity;
When do apocrine sweat glands activate?
Human head hair is the longest of any mammal.
Jaw
- Males more robust and mandible squarer, teeth larger; beard accentuates this male character and hides facial expression, so male tends to
look more stern/authoritative; beard grows 1/60in/day, which would be over 1ft in 2 years; angle of jaw close to 90 degrees, chin square
- Female jaw chin rounded, angle of jaw over 125 deg
Neck
- Males have a larger larynx (why?), so the thyroid cartilage (“Adam’s apple”) is more prominent
- Female clavicle relatively lower compared to scapula, so neck is longer and more gracile
Chest
Upper extremity
- Males thicker & heavier; shoulders broader; arms hang straight down--more mechanically efficient (see next box); males have a triangular
shape from shoulders to waist.
- Females have “permanently” enlarged breasts, which mimic the buttocks; unlike all other mammals, female mammae have two major
functions: feeding the young & sexual signal; with wide hips and enlarged chest, females have an hour-glass shape
- Males stronger upper extremities (more muscle mass--more testosterone); comparing world class athletes: in the javelin, males can throw
up to 33% farther, whereas in running, males are only about 10% faster; on average, males have a power grip that is twice that of a female’s
- Female elbow joint laterally flares about 6 deg farther--less mechanically efficient. Females have more slender digits & looser
interphalangeal ligg (What does this mean in relation to function?)
Back
- Females have a greater lumbar curve, which protrudes the buttocks
Abdomen
Female proportionately longer, & the lower abdomen is rounder
Pelvic bowl
- Males narrow; pubic arch 90 degrees or less; in superior view, pelvic bowl deeper and cone-shaped; ilium extends well above sacrum;
sacrum curve inwards more & coccyx points anteriorly (no room for a birth canal!)—pelvic inlet is heart-shaped; obturator foramen round
- Females wider and more shallow bowl; pelvic inlet larger and rounder; larger pelvic outlet; iliac crest is less curved; ilium less vertical;
greater sciatic notch wide; sacrum short & wide w/more anterior curvature; coccyx points inferiorly; pubic arch over 100 deg; obturator
foramen oval; acetabulum faces slightly anteriorly, not directly laterally as in males; Because pelvis is wider, femoral angle more sharply
medially, so less mechanically efficient; though center of gravity for the body is lower in a female, it’s slightly off center, which adds a
“wiggle” to walk
Buttocks
the permanently swollen buttocks is uniquely human; due to our large gluteal Mm, which are necessary for our funny way of walking, also
serves as a permanent sexual signal--in other primates, genital & buttock swellings occur in the female when in heat;
Reflecting the pelvis shape, males have flatter, narrower hips and buttocks, and females have wider, rounder hips & buttocks
Feet
Females smaller, more gracile (note build of women’s shoes).
2
Disorders/Conditions
Sprain - joint ligg stretched or are torn. As opposed to a strain, which is torn muscle fibers and less severe than a sprain.
Dislocation - bones of joint are forced out of alignment. Very slow healing process. Most common in the phalangeal & shoulder joints, with tearing of
ligg, tendons, & joint capsules.
Osteoporosis - a decrease in amount & strength of bone tissue normally due to decreases in hormone output. Bone resorption outpaces bone formation.
Paget’s disease - characterized by massive osteoclastic resorption & extensive bone formation.
Osteogenic sarcoma - bone cancer affects osteoblasts, primarily teenagers during growth spurt. Multidrug therapy, chemotherapy, or amputate for
treatment.
Osteomyelitis - inflammation, especially marrow; pathogen usually Staphylococcus aureus.
Rheumatism - painful state of bones, ligg, tendons, joints, & Mm.
Arthritis is a class of diseases that exhibit joint inflammation, pain, & stiffness.
Rheumatoid arthritis - most crippling kind of arthritis; autoimmune disease involving severe inflammation of the joints (starting w/synovial
membranes). The body’s immune system attacks its own tissues (cause unknown); causes swelling & ossification of scar tissue, immobilizing the
joint ankylosis.
Osteoarthritis - (OA) - degenerative disease of joints, “wear & tear arthritis.” Deterioration of articular cartilage & bone spur formation,
noninflammatory, & attacks large joints first.
Gouty arthritis - sodium urate crystals deposited in the synovial membrane of joints. Causes inflammation, swelling, & pain. If untreated, joints
fuse. Most common in middle-aged & older males. Caused by abnormal gene, environment, & stress.
Lyme’s disease - bacteria from deer tick Borrelia burdorferi causes rash w/flu like illness. May be followed by cardiac or neurological problems.
Principal complication is arthritis.
Bursitis & tendonitis - inflammation of a bursa & a tendon sheath, respectively. Bursitis is caused by trauma, infection, or rheumatoid arthritis.
Ankylosing spondylitis - inflammation of vertebral & sacroiliac joints. Most common in males 20-40. Results in ankylosis (freeze joint) & kyphosis.
And now for something completely different: The nursery rhyme Ring Around the Rosey is a rhyme about the plague. Infected people with the plague
would get red circular sores ("Ring around the rosey..."), these sores would smell very badly so common folks would put flowers on their bodies
somewhere (inconspicuously), so that it would cover the smell of the sores ("...a pocket full of posies..."). People who died from the plague would be
burned to reduce the possible spread of the disease ("...ashes, ashes, we all fall down!"). ]
[ Age Related Skeletal Changes ]
[ Region
Surface features & matrix density
Age Norm
45 f
60 m
Event ]
Skeletal mass and features reduce with the onset of “middleageitis,” accelerating greatly for
postmenopausal females & males over 60
cranial sutures
22-42
complete closure of sutures can vary greatly, and some may never close
fontanelles
by 2
closure of cranial “soft” spots of cartilage; post fontanelle closes by 2mos & ant by 18mos
occipital bone
1-4
complete ossification
styloid process
12-16
fuses to temporal bone
hyoid bone
25-30
complete ossification
first bone to ossify in a fetus; it’s a dermal bone that begins ossifying in the 5 th week
clavicle
deciduous or milk teeth
0.5-2
medial incisor 6mos; lat incisor 10mos; 1st premolar 14mos; canine 18mos; 2nd premolar 22mos
note that they erupt at about 4mo intervals starting at 6mos & are replaced at yearly intervals starting
at 7 or 8; there may be up to a year between a deciduous tooth being shed & then replaced
permanent or adult teeth
7-24
medial incisor 7-8 yrs; lat incisor 9; 1st premolar 10; canine 11; 2nd 12 premolar; 1st molar 6; 2nd
molar 12; 3rd molar 24
mandible
60+
loss of teeth; reduction of mass; change in angle at mandibular notch (angle between condyloid &
coronoid processes)
xiphoid process of sternum
25-29
fusion to body of sternum
vertebral curvature
infant to
toddler
development of cranial & lumbar vertebral curves caused by holding head upright, crawling, &
upright walking
intervertebral discs
60+
reduce in size; lose height; accelerates after 60 (I’m shrinking!)
long bone epiphyses
15-18
epiphyseal fusion varies but can be useful in age determinations
pectoral & pelvic girdle epiphyses
14-16, 1618, 22-25
ranges overlap and can vary a bit for epiphyseal fusion, but better indicators for age estimates than
long bone epiphyses