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.