no strong social bonds in the herd. These herds are sometimes very open and loosely defined as sometimes females come and go. Males born in the herd will remain in the herd until they developed their primary and secondary sexual characteristics. Once they have developed these traits males leave the herd and become nomads. It is only during the breeding season males congregate around a female in estrus for a few hours. All spiral-horned antelope species are polyandrous. Aggression is very low among individuals of both sexes though intraspecific competition does occur. In females often they neck-fight as well poke and snap at each other. Males would use their horns for wrestling where they try to attack the face. Sometimes there is even intimation from the males to persuade the female into submission as often she would try and retaliate. The gestation period occurs once the female has been inseminated from the male successfully. In most species it lasts approximately seven months, although in the larger species this extends to eight or nine months. They only give birth to a single calf. Once the young are born, they won't wean until they are around five to six months of age. Females sexually mature by two to three years while for males it is four to five years. Genetics and hybridization The chromosome number of various species varies. This correlates nicely with the evolutionary relationships among the spiral-horned antelopes. The ancestral Y chromosome was subacrocentric but a pericentric inversion occurred making it submetacentric after the separation of the lesser kudu and nyala. Ancient hybridization also played a key part in the evolution of the chromosomes in all species. Below is a listing of the diploid number 2n as follows (male/female): Nyala: 2n = 55/56 Lesser kudu: 2n = 38/38 Common eland: 2n = 31/32 Greater kudu: 2n = 31/32 Bushbuck: 2n = 33/34 Sitatunga: 2n = 30/30 Bongo: 2n = 33/34 Hybridization between bongos and sitatunga produce fertile offspring known as "bongsis" and are well documented. These hybrid animals have a diploid number 2n = 33 and all known cases produced female animals, which had developed horns like female bongos while their stripping pattern was intermediate between bongos and sitatungas with an overall orange coloring. The hybridization of these species adds further support in the bongo and sitatunga being each other's closet relatives. Other hybrids have been documented, such as a