Subsistema de Recepción

T he m o st obvious genetic difference b etw een m a le s a n d fem ales

is th e c h ro m o so m a l c o n stitu tio n , fem ales b ein g th e h o m o g am etic sex

46, XX a n d m ales th e h e tero g am etic sex, 46, XY. T he Y c h ro m o so m e

is believed to c o n ta in relatively few active g en es (G raves 1998), th e

m o st im p o rta n t in sex d e te rm in a tio n b ein g th e SRY gene, often

referred to a s th e m ale d e te rm in in g gene. T his gene is clearly involved

in g o n ad o g en esis b u t w h e th e r or n o t it is th e only gene re sp o n sib le

for m a le /fe m a le p h y sic al differences is u n reso lv ed .

The ta s k of d is tin g u ish in g g e n d er from s ta tic facial c u e s alone,

in th e a b se n c e of h a irsty le, m a k e u p a n d o th e r c u e s is m o re difficult,

th o u g h h u m a n s still p erform q u ite well (B u rto n e t a l 1993). T here a re

g en eral differences b etw een th e sex es th o u g h t to be a n im p o rta n t

facto r in a id in g sex d ifferen tiatio n . The m u sc le s of th e fem ale face are

g enerally less s u b s ta n tia l a n d b e tte r h id d e n by fatty tis s u e , a n d th e

fem ale n o se is p ro p o rtio n a te ly sm aller, w id er a n d m o re co n cav e w ith

th e bridge of th e n o se often b ein g d e p re sse d . T h ese le ss r o b u s t, less

m obile fe a tu re s a re believed to m ak e th e fem ale face a p p e a r y o u th fu l

a n d childlike, q u a litie s p o s tu la te d to be a sso c ia te d w ith fem in in ity

(Ligget 1974).

S ex u al d im o rp h ism in h u m a n s is n o t a s m a rk e d a s in som e

o th e r p rim a te s (M asterso n a n d H artw ig 1998). T he a c tu a l difference

b etw een m ale a n d fem ale faces is relatively difficult to q u a n tify , a s its

d ev elo p m en t a n d en d o crin e v a ria tio n s. S ex u al d im o rp h ism is

g enerally e ith e r difficult to m e a s u re or e x p re sse d in te rm s of a n

index; s u c h a s p ro tru s io n of th e m an d ib le o r c ra n io fac ia l index.

H ow ever th e re a re co m p reh en siv e d a ta available o n h u m a n sex

differences (Keen 1950; F a rk a s 1994).

F rom b irth , th e h e ig h t of th e m idface, from eye level to th e level

of th e n o strils, grow s stead ily u p u n til ad o lescen ce, m o re so th a n th e

r e s t of th e face. T here is little se x u al difference in sk u ll size u p u n til

p u b e rty by w h e n 90% of th e a d u lt c ra n ia l size is a tta in e d (H um phrey

1998). A fe a tu re a sso c ia te d w ith a y o u n g e r face is t h a t a y o u n g

c h ild ’s n o se is g enerally sm all, w ide a n d concave w ith a s u n k e n

bridge, th e n o se develops along w ith th e grow th of th e m idface u n til

ad o lescen ce. A dolescence b rin g s a b o u t fu rth e r c h a n g e in face sh a p e ,

th e o n se t of p u b e rty in m ales b rin g in g a b o u t grow th a n d defin itio n of

th e m an d ib le, a n d in fem ales th e lo ss of ‘p u p p y f a t’ r e s u ltin g in a

m o re w om anly face (Enlow a n d H a n s 1996).

D erm al c h a n g e s a re m ain ly re sp o n sib le for th e c h a n g e in

a p p e a ra n c e t h a t we a sso c ia te w ith older age, th e lo ss of elasticity ,

p ig m e n ta tio n sp o ts, th in n in g a n d w rin k lin g of th e sk in . W rinkles

often first a p p e a r on th e tra n s v e rs e lin es of th e fo reh e ad , a lo n g th e

line b etw een th e o u te r m o u th a n d th e n o se a n d a ro u n d th e eye a rea.

In te rm s of ageing a n d g en etics relatively little is k n o w n , how ever,

a sso c ia te d w ith p re m a tu re ageing, s u c h a s C ockayne sy n d ro m e

(Nance a n d B eriy 1992).

T he m o st n o ticeab le differences b etw een faces a re generally

a ttrib u te d to differences in e th n ic b a c k g ro u n d ; th is is a n overall

g e sta lt of fe a tu re s r a th e r th a n a sin g u la r fe a tu re . M any s tu d ie s have

b e e n c a rrie d o u t on e sta b lish in g cran io facial s ta n d a r d s for different

e th n ic p o p u la tio n s (R ichardson 1980; C h u n g e t al 1982 S h a lh o u b et

al 1987; H u a n g e t al 1998; F a rk a s 1994). Id eas a s to w h y different

e th n ic g ro u p s h av e evolved w ith d istin c t facial p h e n o ty p e s hav e

in c lu d e d th e h y p o th e sis of e n v iro n m en ta l a d a p ta tio n (C arey a n d

S te e g m a n n 1981). T h a t is t h a t d u rin g th e c o u rse of ev o lu tio n wide

a n d flat faces like th e M ongoloid faces w ere selected for in cold

clim ates a s a face type w ith no ‘ju ttin g p a r t s ’ is d e fe n d ed m o re easily

from th e cold. The in cid en ce of o th e r facial v a ria tio n s s u c h a s s u tu r a l

v a ria n ts a s well a s n o n -m e tric v a ria n ts h a s also b e e n closely looked

a t in different p o p u la tio n s (Berry a n d B erry 1967).

D ifferences in p ig m e n tatio n pro v id es th e m o st p ro n o u n c e d

v isu a l differences b etw een in d iv id u a ls of d ifferen t e th n ic origin a n d

m u c h w o rk h a s b een d o n e to try to u n d e r s ta n d th e g en etic b a s is of

sk in c o lo u ra tio n (Robins 1973; N ichols 1973). S u c h w o rk s c o n clu d e

th a t th e g en etic b a s is of sk in a n d eye p ig m e n ta tio n is likely to be

ex trem ely com plex involving c o n sid era b le n u m b e r of g en es. How ever

re c e n t s tu d ie s h av e a sso c ia te d th e m e la n o c y te -stim u la tin g h o rm o n e

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