Some of the earliest examples of sophisticated
sculpture in sub-Saharan Africa come from the
Nok culture, an Iron Age civilization that has
been dated between 900 B.C. and 200 A.D. The
terracotta sculptures range in size from small
pendants to life-size figures. We do not know
what the people called themselves, so the
civilization was named after the small tin-
mining village of Nok where the first objects
were discovered in 1928. Archaeological
artifacts have been found in throughout Nigeria,
primarily to the north of the Niger-Benue River
confluence and below the Jos escarpment
detailing the extent of their cultural influence.
According to some accounts, based on artistic
similarities between early Yoruba art forms and
Nok forms, there may be connections between
Nok culture and contemporary Yoruba peoples.
What is clear is that certain stylistic tendencies
prevalent in black African art today may have
originated in the sculptures of the Nok.
The phenomenon of twinning is considered a
sacred blessing in various contemporary African
cultures, specifically the Yoruba. Perhaps this
belief dates back to the period of the Nok, as this
sculpture suggests. Memorialized in clay, this
couple represents a pair of conjoined, or
Siamese, twins. Conjoined twins are one of the
most rare forms of twinning and would certainly
be interpreted as a most ominous event. This
sculpture lovingly captures the beauty and
spectacle of this natural wonder. While the
sculpture first appears to be a seated couple, one
soon realizes these figures share a leg and are
connected at the torso. Their banded jewelry not
only decorates their limbs but also unites them.
Although they wear two necklaces in the front,
the necklace appears as one in the back,
symbolizing the bond they share. This gorgeous
sculpture must have honored a most spectacular
pair of beings, either during their lifetime or in
death. The closeness between the two is
eternally evident, masterfully conveyed by the
Conjoined Twins Presenting With Different Sex:
Description of a Second Case That Truly Represents
the Earliest Historical Evidence in Humans
Marı ´a Luisa Martı ´nez-Frı ´as1,2,3*
1Centro de Investigacion sobre Anomalıas Congenitas (CIAC), Instituto de Salud Carlos III, Madrid, Spain
2Facultad de Medicina, Madrid, Spain
3CIBER de Enfermedades Raras (CIBERER), Madrid, Spain
Received 24 April 2009; Accepted 27 April 2009
TO THE EDITOR:
It iswell known that conjoined twins are monozygotic (MZT), their
most accepted mechanism being an interruption of the splitting of
the inner cell mass before the total separation, giving rise to the
different types of conjoined twins. There is another, but less
accepted theory, postulating that conjoined twins occur as a result
of the fusion of monoamniotic twins. However, in any mechanism
and type of conjoined twins, they are always of the same sex.
In 2007, Kim and co-workers published what appears to
be the first, and the only, reported case of conjoined twins
(cephalothoracopagous), presenting external and internal genitalia
of morphologically different sexes. In spite of their distinct
sexual appearances, microscopic examination showed that
internal genitalia had oocytes in both twins, and chromosomal
studies documented that both were females (XX). Regarding
the mechanisms behind their formation, Kim et al.  considered
that because of the observed genital differences, this
case supports the fusion mechanism of monoamniotic twins
rather than the incomplete fission of an embryo; but they did not
Indeed, as those authors commented, the case they present is
exceptional, and the first documented in the literature. However,
I would like to describe what I consider to represent the very first
known case in Human History.
This is represented in a beautiful figurine from Nigeria
that was dated to be from a period ranging from 300 years BC to
500 of the Christian era (Fig. 1). The figurine shows pair of
conjoined twins in which we can recognize the type of dicefalustri-
brachius-tripus monozygotic twins, since two of their legs
were fused. Interestingly, the artist represented one twin as
female since she has breasts, and a male who also appears to be
taller than the female co-twin. Therefore, I consider that the
author of this figurine artistically represented a real case of conjoined
twins that might have been born with, in some way, different
FIG. 1. The series of photos of the figure is courtesy of Barakat, Inc.
and can be viewed at http://www.fayezbarakat.com. [Color figure
can be viewed in the online issue, which is available at
Grant sponsor: Fundacion 1000 sobre Defectos Congenitos.
Marı´a Luisa Martı´nez-Frı´as, Facultad de Medicina, Departamento de
Farmacologıa, Universidad Complutense, c/Sinesio Delgado 6, Pabellon
6, Madrid 28029, Spain. E-mail: firstname.lastname@example.org
Published online 16 June 2009 in Wiley InterScience
How to Cite this Article:
Martınez-Frıas ML. 2009. Conjoined twins
presenting with different sex: Description of a
second case that truly represents the earliest
historical evidence in humans.
Am J Med Genet Part A 149A:1595–1596.
2009 Wiley-Liss, Inc. 1595
external genitalia, as occurred in the case described by Kim et al.
This work was supported by the ‘‘Fundacion 1000 sobre Defectos
Congenitos’’. CIBERER is an initiative of the Instituto de Salud
Carlos III, Madrid, Spain.
Kim SC, Jo DS, Jang KY, Cho SC. 2007. Extremely rare case of cephalothoracopagus
characterized by differences of external genitalia. Prenat
FIG. 1. (Continued) Diagn 27:1151–1153.
1596 AMERICAN JOURNAL OF MEDICAL GENETICS PART A