Same-sex penguin couple Electra and Viola become parents after they hatch an adopted egg at Valencia aquarium

• The two female penguins had shown broody behaviours by building a stone nest
• So aquarium staff put an egg from another penguin into Electra and Viola's nest  
• The 'exceptional couple' are the first same sex parents at the Valencia aquarium
• A same-sex penguin couple have become parents after the egg they adopted successfully hatched at Valencia aquarium.
  The two female penguins, Electra and Viola, at Oceanografic Aquarium in Valencia, Spain, hatched another couple's egg. 
  Although the two penguins are infertile together, aquarium staff placed the egg from another penguin in their nest after they appeared to be broody. 
  Same-sex couples are common in more than 450 species in nature, although this is the aquarium's first same-sex couple. 
  
  

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  The proud parents were able to adopt, incubate and raise the egg of another couple at the aquariumElectra and Viola are female and have been able to adopt, hatch and raise an egg from another couple, something that's happened for the first time at the Oceanogràfic,' the aquarium said in a blog post, calling them an 'exceptional pair'.

  The as yet unnamed addition is one of three chicks born so far to the colony of 25 Gentoo penguins (Pygoscelis papua) at Oceanogràfic this breeding season. 

  The three couples that have raised chicks so far have been two heterosexual pairs Navi and Aquela and Bolo and Melibea, as well as Electra and Viola. 

  The pair of females had begun to show typical penguin behaviours prior to reproduction, such as building their own nest out of stones.

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  Staff translocated a fertile egg from another couple when they saw that they began to carry out habitual actions prior to reproduction

  Seeing this, aquarium staff moved a fertile egg from another couple and placed in Electra and Viola's nest, who successfully carried out the entire breeding process.

  Electra and Viola aren’t the first same-sex penguin couple to raise a chick, however, as homosexuality is common in penguins. 

  At Berlin Zoo last year, male couple Skipper and Ping adopted an egg that had been abandoned by its mother. 

  The two had previously displayed their instincts as nurturers by trying to hatch stones and even fish.

  In London's Sea Life Centre, meanwhile, a chick adopted by a pair of female penguins last year is being raised as gender-neutral by its keepers. 

  'While the decision may ruffle a few feathers, gender neutrality in humans has only recently become a widespread topic of conversation,' Graham McGrath, the centre's general manager, said at the time.

  'However, it is completely natural for penguins to develop genderless identities as they grow into mature adults.'  

  
  

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  The new chick. The eggs hatch at 38 days and the chicks usually become independent at 75 days

  
  

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  The shy penguin chick hides under its same-sex parents. Homosexuality is common in penguins

  
  

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  A penguin chick (pictured) that's being raised gender-neutral by keepers at the London Sea Life centre  

  Penguin reproduction normally begins with the construction of the nests that consist of round pebbles, which can reach more than 7 inches on each side, the aquarium said.

  Stones are a very precious commodity for these animals and can even be part of the courtship ritual normally initiated by the male.

  During courtship, the male will find the smoothest pebble to present to the female as a gift and a symbol of his affection. 

  If the female likes the gift, she will place it in the nest and the two will continue building up a pebble mound in preparation for the eggs. 

  The father and the mother then take turns every day to keep the egg warm during incubation. 

  The eggs hatch at 38 days and the chicks usually become independent at 75 days with an approximate weight of 6 to 7 kilograms. 

  Emperor and king penguins are the exception to stone nest-building, which lay one single egg, rest it on their feet and keep it warm under a feathery fold of skin.       

  
  

  HOMOSEXUALITY IN ANIMALS

  Homosexuality in nature appears counter-intuitive but is observed in a range of species around the world. 

  There has yet to be an accepted explanation based on neurological, chemical or behavioural factors to explain why some animals are homosexual and some or heterosexual. 

  Some scientists say it may be due to exposure to testosterone levels in the womb, although this remains a hotly debated topic which has yet to be proved. 

  In a book titled: 'Homosexual Behaviour in Animals: An Evolutionary Perspective', the author, UCL professor Dr Volker Sommer, writes: 'Within a select number of species, homosexual activity is widespread and occurs at levels that approach or sometimes even surpass heterosexual activity.'

  Homosexual behaviour has been observed in many animals, including: macaques, dwarf chimpanzees, dolphins, orcas and humans. 

  Some studies claim homosexuality may be a common as being found in up to 95 per cent of all animal species. 

  There are two principle schools of thought when it comes to the prevalence of homosexuality in nature.  

  One theory states that homosexuality in animals doesn't need an explanation, with animals being homosexual just as naturally as they are heterosexual. 

  It appears irrational for it to survive as a trait as it hinders the ability to procreate directly, but many speculate it allows individuals to ensure their genetic material is passed down the generations indirectly as they are able to look after members of their family with offspring.   

  For example, helping nurture the offspring of a sister.   

  Similar behaviour dedicated to the 'greater good' of a large group have been seen in various species. 

  For example, in familial wolf packs only one pair of animals breeds - the alpha and the beta. The other animals ensure the protection, feeding and nurturing of the litter.

  This allows their genetic material to pass indirectly to the next generation through their sister, brother, mother etc or whatever the relationship may be. 

  The same school of though applies to animals which have exceeded their reproductive age. 

  For example, female elephants which are now too old to have offspring. 

  They still play a crucial role in the protection of the young a the matriarch leads the group to spots of food, water and chases of would-be predators.

  These actions ensure the survival of the young and vulnerable members of her family, again helping ensure her genetic material is passed down through the generations indirectly.  

  A similar concept can be applied to homosexuality, some experts claim. 

  Without the ability to reproduce directly, they are able to expend energy looking after the offspring of their family members. 

  Another theory states that homosexual behaviours aid in the successful passing on of genes in the long-term as young animals 'practice' mating techniques and ways of attracting a member of the opposite sex.

  Rates of homosexuality in different species continues to be unknown, as ongoing research finds more nuances to homosexuality in nature. 

  It continues to be found in more species but the level of homosexuality in individual species is not well enough studied to be able to determine if homosexuality is becoming increasingly common.