The existence and great abundance of a unique form of pig intersexuality was verified on the northernmost islands of Vanuatu.

Morphological examinations were conducted on 54 pigs from the islands of Malo, Ambae, and Aore. Through blood analysis, estradiol and testosterone levels were derived. Subsequent comparisons of the estradiol/testosterone ratio yielded results consistent with "maleness". Fifty-one dental and mandibular measurements of the Vanuatu Sus. sp. specimens plotted within the feral swine target group.

Behaviorally, the Vanuatu intersex pig exhibits periods of aggressiveness that generally coincide with a sow in heat. When encountered in the "bush", the naravé (local name for the intersexual pig) is a stronger and more aggressive adversary than the "normal" native wild pig. Six gross dissections yielded totally male internal sex organs. Four separate graduations or phases of the intersexual condition are described according to their external genitalia. The phases of intersexuality appeared to be an inherited trait. Certain sows (called falé-ravé) are known intersex producers and 20% of their offspring will be intersexual.

Vanuatu, a relatively young landform, appeared 22 million years ago when a series of massive deep ocean earth movements forced a chain of submarine volcanos to the surface(8). In addition to being a remote island group,  Vanuatu has not had the time to evolve and develop the rich array of mammalian species as some of its closest mainland neighbors.  Only six species of mammals are indigenous to these islands; all are bats, representatives of the suborders Megachiroptera (Flying foxes) and Micorchiroptera (insectivorous bats).

Most historians agree that the peoples of the Western Pacific originated in southeast Asia about 40,000 years ago, and through a series of migrations across Indonesia and the New Guinea chain, these people colonized many islands, including the Solomons and Vanuatu beginning about 3,000 B.C.(8).

The earliest evidence of human occupation and settlement discovered in Vanuatu comes from a site on Malo Island in the northern part of the country. Archaeologists (9) claim that in about 1400 B.C., the most adventurous of these proto-melanesians (people of the Lapita culture) traveled by canoe and brought with them yams, taro and the predecessor of the native pig, ​Sus papuensis.  This corresponds somewhat indirectly with some of the Malo peoples interpretation of the origins of the first life forms on that island. Through oral traditions, many locals still believe that the first humans to settle Vanuatu were also from Malo, but that they arose from a hole in Malo Pass.  From this hole, along with the first man, also came the first Naravé (The national language of Bislama"s term for the intersex pig).  Many people of Malo believe that their island was the first site of human and animal habitation.  Contrary to popular European misconceptions, the first pig in the Islands did not arrive with Captain Cook in 1774, but with successive migrations of peoples from Northern Melanesia in much earlier times (1).  Marshall (10) stated that, "No anthropologist would admit for one minute that such a elaborate and complex pig culture could be established in less than several centuries and it would be a biological impossibility anyway for it took centuries, co-related with native culture, to produce this incredible ratio of bisexual animals."

Sus sp.(Incorrectly termed Sus papuensis,these pigs are S. scrofa vittatus X S. celebensis hybrids)(11)(30), the ingigenous pig which is still thriving today, seems to have to adapted extremely well to the climatic and geographic conditions of Vanuatu. These pigs can be found on almost every island in Vanuatu in both the domesticated and wild states.

The most predominant characteristics of these pigs are those of hardiness, compact size and a long tapering snout. Much smaller than its European counterpart Sus scrofa, the adult boar will generally weigh no more than 100 kilograms. Hope (12) wrote in 1872 that "We found no difficulty in getting as many pigs as we liked for an adze apiece, but they were by no means in fine condition, and if it is true that these pigs are descendants of those left by Captain Cook in the last century, then they must have been wonderfully altered ... they are shaped like a West Indian peccary, black and hairy, long in the leg and hollow in every part they should be full, the only point in which they excel is biting".

Sus sp. (incorrectly termed Sus papuensis) pigs are S. scrofa vittatus X S. celebensis hybrids) (11) (30), the ingigenous pig which is still thriving today, seems to have to adapted extremely well to the climatic and geographic conditions of Vanuatu.  These pigs can be found on almost every island in Vanuatu in both the domesticated and wild states.

The most predominant characteristics of these pigs are those of hardiness, compact size and a long tapering snout.  Much smaller than its European counterpart Sus scrofa, the adult boar will generally weigh no more than 100 kilograms. Hope (12) wrote in 1872 that, "We found no difficulty in getting as many pigs as we liked for an adze apiece, but they were by no means in fine condition, and if it is true that these pigs are descendants of those left by Captain Cook in the last century, then they must have been wonderfully altered ... they are shaped like a West Indian peccary, black and hairy, long in the leg and hollow in every part they should be full, the only point in which they excel is biting".

The colors of the native pig range from off-white to black.  All colors and color patterns (i.e. spotted belted, and differential point coloration) (Hetzer(31)) are represented in these pigs, with the predominant color being an agouti/grizzled, ranging from light brown to black with lighter distal tips on the bristles.  By proportion there seems to be a lower proportion of white and lighter colored animals apparently because they suffer severely from sunburn and do not thrive in these conditions and, thus have been naturally selected against(11). Sus spp. has a leaner body build as compared to the commercial high production varieties who have proven to be uneconomical in this humid tropical environment.

According to Weightman(12), Paddon probably introduced the first European breed of pig when, in 1845, he brought many kinds of livestock, including pigs, from Australia to Aneityum, an island in Northern Vanuatu. There have been, as one might expect, many subsequent crossings of the European with the native pig.  According to local oral tradition as related by Cheif Joseph of Molo, along with the smaller body size comes a lighter body frame and skeletal system as exemplified in the skull thickness.  I have been told on many occasions that "during the "Nimangki" (a ceremony celebrating a Ni-Vanuatu man's social climb), it should only take one powerful blow of the carved hardwood club to shatter the skull, thus killing the pig, whereas very often it takes several strikes to kill a European pig or one with European blood".

Many of the wild pigs are found in the dense bush and are joined there by wild cattle, dogs, and cats who have escaped disadvantaged domestic situations. These wild pigs are extremely nervous and wary of human encroachment. Sows with very small piglets and rutting boars in the presence of females in estrus, have been responsible for aggressive attacks on humans and animals. One thing to be noted though, is the excellent physical condition of these wild pigs as compared to their domesticated cousins. In the wild state they are able to realize the potential of their breed and thrive. Domesticated pigs of both European and wild blood, who are generally penned or tethered, are frequently ravaged by unchecked infestations of kidney worms (Stephanarus coleri)(12).

The sow is a good mother, giving birth to and successfully raising a limited number of piglets per litter (averaging 4 to 5 offspring) every 12 to 18 months in uncontrolled breeding situations (13).  The young, being extremely precocious, can survive on their own after one week of age.  All Piglets, however, do not have juvenile striped markings as stated by Weightman (12), but are born with the color and pattern they will possess at maturity.  Of the 109 piglets observed in this study none was striped.  One elderly pig pig owner recalled observing striped young in his youth.

Young sows have been bred as early as 6 months of age but generally a female is beyond one year of age when she first farrows. Piglets may be born in any month of the year and the gestation period seems to fall within the range of many other species of pigs (112 to 120 days). The average litter size of today's high production domestic swine is eleven piglets with the sows farrowing at least two times a year (14). The small size of Vanuatu's pigs and their reduced litter size have been mistaken for inbreeding in the past, but it is more appropriate to say that it is most likely an adaptation to maximize the nutritional, climatic, and geographical conditions available to residents of this tropical Archipelago.

Archaeological findings concur that the earliest evidence of permanent human occupation in Vanuatu comes from a site on Malo, an island off the southeast coast of Espiritu Santo.  This area was first settled around 1400 B.C. by the peoples of the Lapita culture and along with them in their canoes they brought a unique style of pottery, subsistence vegetables and domestic animals such as poultry, dogs and pigs (9). 

It is not hard to believe that through years of isolation, particularly on an island the size of Malo (17 km. long and 13 km. wide), that some degree of inbreeding must have occurred. It was perhaps as a result of one of these close matings that the first intersexual pig appeared. Through successive generations, and because of the value placed on this "unique" pig, it was no doubt recognized by these intelligent people, that even though the intersexes themselves were incapable of perpetuating their own kind, certain female pigs (the falé-ravé as they came to be called) occasionally produced these intersexual offspring while others did not. In addition to the dam of the Naravé, occasionally a female sibling of the intersex becomes a Naravé producer herself. Thus the sows carrying the genes were also highly valued and as a result of artificial selection, this small obscure bit of Melanesia now has, by far, the greatest ratio of porcine intersexuality yet discovered.

Because of the rarity of this sexual aberration, and the fact that these pigs could produce the highly valued curved tusks, these pigs became prized possessions in the cultures that practiced "Nimangki" or grade-taking.  It was from this time that the people of Malo Island began purposefully breeding a pig that could help them to more swiftly achieve the status of chief, as well as being important monetarily in trade with the people of neighboring islands.

It is also a fact that Malo, in time, became the center of a trade route connecting northern coastal Malakula with the main island of Santo and Tangoa Island (12). This trade route enlarged to include much of northern Vanuatu.  It was along these routes that pandanus leaves, shell money, and domesticated animals were readily traded.  It is my contention that the very first Naravé pigs were systematically bred on Malo Island, and then distributed throughout the northern islands of the Archipelago during trading sessions in return for goods and services. Further evidence of this could be obtained from the DNA of skin samples of intersex pigs from several remote areas of Vanuatu to ascertain their relationship, if any, to each other.

CBC'S of the ten animals all fell within, or on the periphery of the range of norms for swine (Table 1).  The research animals consisted of pigs ranging in age from approximately one to seven years.  All animals came from the same area on Malo Island.

Upon first observation (Table 2), the hormonal values of the representative samples cannot by themselves be interpreted.  The ratios of estradiol to testosterone were generated and the following general conclusions may be drawn.  Ratios greater than unity have been generally designated as female and those less than one generally designates maleness (27).  Like the two normal males, all seven of the intersexes showed ratios less than 1.0.

These observations seem to support the theory that Vanuatu's intersexual pigs are actually mal-developed boars. Pig "B", said by locals to be a pregnant female, showed a progesterone level of 10.6 ng/ml, consistant with that of a pregnant sow.

The results of the Dihydrotestosterone (DHT) test on the sera of pigs D,E,F,J,K,L,M were consistent with maleness. Of the 54 animals on which external examinations were conducted, there was a high degree of variability, the most common occurrences were in testicular (number, size, and location) and urogenital configuration. Findings for the intersexes varied from very "female" looking external genitalia with no testicles to a descended scrotal sac containing two large well-developed testicles. Within this range were many different testicular presentations including an empty scrotal sac, one degenerate descended testicle, one large testicle, and one large and one small testicle represented. Of the animals examined, 61% or 33 animals exhibit no testicles whatsoever, 10 (or 19%) possessed 2 well-formed scrotal testicles, 8 (or 15%) had 1 normal descended testicle, and the remaining 5% had 1 small and 1 large or 1 small testicle present. As the intersexes' testicular development approached that of the "normal male" condition, there was a corresponding change in the position and length of the ventral labial commissure (V.L.C.) and the urogenital aperture. When there were no testicles or scrotum present, the vulva seemed almost undifferentiable from that of the normal female organ except possibly for a slight reduction of the urogenital opening, and the presence of the corpus cavernosum (C.C.) may push the (V.L.C.) dorsally and laterally. The terminal end of the urethra is distinguished from the corresponding structure of the normal female by the presence of the bulbo-cavernosus. Correspondingly, as the testicles become larger and descend into the scrotum, the V.L.C. appears to become larger as the C.C. itself enlarges and begins to turn ventrally, taking the V.L.C. with it. The most developed phase that was examined was that of the "transitional" male pseudohermaphrodite in which two large testicles were situated in the scrotum and the projection, now much longer than before, consisting of the V.L.C., the C.C. and the terminal end of the urethra, was situated directly anterior to the scrotum. Despite all of these varying phases of genital development, each of these animals, as an adult, consistently exhibited tusks, with a base diameter consistent with that of the male of the species. As expected those animals exhibiting 1 external testis (whether it appeared normal or degenerate) also contained 1 degenerated testicle within the abdomen. In one case, however, a young animal(Pig A) with no external testicles or scrotum, possessed only 1 small but well-formed testis inguinally. No vestige of the other testicle was detected. In most cases, the testicles appeared to be more or less degenerate or totally so. The vulva had a reduced urogenital aperture. There were never any rudiments of vagina, cervix, uterus, oviduct or ovaries evident in any of the intersex pigs examined, which concurs with Baker's findings in 1928(4).The urine was delivered from the bladder via the urethra to the external opening anteriorly corresponding with its specific phase of intersexuality. At the terminal end of the urethra there was a bulbo-cavernosus muscle which aids, in normal males, in expulsion of urine or sperm. In all cases, the internal anatomies were wholly male, although in various stages of development. Seminal vesicles, bulbo-cavernosus muscle, and corpus cavernosus were evident in every individual. Bulbo-urethral glands were found in all but one individual.

After six weeks of following empty leads, the first intersexual pig was observed on the island of Aore in Northern Vanuatu. During the following month fifty-three additional examples of this rare mammalian anomaly were documented. External descriptions and approximate ages and weights of these animals were recorded. Behavioral studies yielded indications of patterns of aggressiveness with the Intersexual pigs kept in villages.

These periods often coincided with the heat cycle of a sow in the vicinity. When encountered in the bush, locals attribute an increased display of aggressiveness and strength to this intersexual condition.  I was able to plot the Naravé's current distribution which is greatly reduced as compared to the original references in the early part of this century.  Approximately 20% of all offspring born to the falé-ravé (intersex producing female) will themselves be intersexes. This conservative estimation is still very impressive and the abundance of these pseudohermaphrodites is equaled nowhere in the world. From local lore and description it is the dam who is the sole contributor to the intersexual condition.

After studying the internal anatomies of six Naravé, the findings were consistent.  With the exception of the external vulva-like organ, there were never any rudiments of female internal genitalia. There were however, generally two testes (either intra-abdominal or scrotal), seminal vesicals and bulbo-urethral glands. These animals were actually "modified" boars and more correctly termed male pseudohermaphrodites.  These individual's embryonic testis had secreted their hormone during a "later" part of development than is necessary to hormonally produce a normal sexually developed male. In regard to the external genitalia, four distinct phases were identified and documented.  

Eleven animals were selected for blood examination of which; eight were intersexuals, two were males and one was a pregnant female. All eleven animals fell within or on the periphery of the range of cbc norms for swine.  Hormonal of estradiol and testosterone were generated from each of the test animals. The ratio of estradiol to testosterone yielded numbers consistent with "maleness" from the two males as well as the eight intersexuals these results support my theory that Vanuatu's intersexual pigs are actually mal-developed boars. 

Although many locals insist that it is the female that is the sole contributor to the intersexual condition, (falé-ravé, mother or sister of an intersex, the soké-rave is the brother of an intersexual), a comprehensive controlled breeding program with test-crosses is necessary to corroborate this.  In normal village "management" situations, chance breeding occurs and the sires are rarely known.  There is a distinct possibility that two carriers for the trait (soké-ravé and falé-ravé) must come together in order to produce the abnormal condition in some males and not in others.  A compliment to controlled breeding would be artificial insemination.  Because of the positioning of the "penis" in all of these intersexes, normal reproduction is a physical impossibility. 

The possibility of electro-ejaculation and artificial insemination, using the intersex as a donor, must not be overlooked. Baker (15) stated, "There appeared to be a few abnormal sperms in the testes of one of the nine individuals while all of the others examined lacked spermatogenesis altogether". With the size and appearance of the testicles on many of the mature animals,  I have no reason to doubt the possibility of the presence of viable sperm.  The simple solution to the genetics of the abnormality as stated by Baker (4) is probably more complex.  The sex-linked inheritance conclusion as proposed by Baker is more than likely a polygenic trait with incomplete dominance (this explains the many graduations of the condition).  There is also the possibility of secondary modifier genes either on the sex or autosomal chromosomes.