Most animals were originally brought into households to work, as hunting dogs or using cats to catch mice for example. But the advantages of keeping a pet go far beyond simply using them as labour.
Pets are widely accepted as having a beneficial effect on your health, but animals can also have a positive impact on your emotional and mental wellbeing, too.
One of the seminal studies into the effects of pets on our health was conducted by the scientists Mugford and M'Comisky in 1975. They studied a group of elderly people for two years. They gave one third of the group a television, one third a houseplant and the final third a budgerigar to look after.
At the end of the study they discovered that the budgie owners felt they had better ties to their communities - they had more visitors to their homes - and felt more fulfilled.
"A lot of older people feel that they are no use to anyone any more," says Dr June McNicholas, a leading psychologist in human-animal interaction. "But this study proved that people have a great need to be needed. For the elderly to suddenly find they had something that needs and appreciates them was wonderful."
The elderly are not the only section of society to benefit from keeping pets. A study carried out by Dr McNicholas and the University of Warwick in 2002 discovered that children who grew up with pets were healthier than their peers who did not.
The study found that children between the ages of five and seven had stronger immune systems and less time off school due to illness. "Pet owning children had up to 18 days better attendance," says Dr McNicholas.
Many other studies have confirmed the idea that keeping a pet has a positive effect on your health. In 1999, the American Heart Association put the belief that pets can help lower your blood pressure to the test.
Researchers from the State University of New York gave pets to a group of stockbrokers suffering from high blood pressure. Another group, also with high blood pressure, was not given pets. After six months, both groups were put into stressful situations - such as trying to calm a client who lost money because of their advice - and had their blood pressure measured. The researchers found that pet owners only had a small rise in blood pressure while non-pet owners had a much greater increase.
In 1995 the Australian National People and Pets survey discovered that pet owners visited their doctors less often than their pet-less friends, and were at less risk of suffering heart attacks and strokes.
However, the major reason given for pet owners' better physical health was that they are more active than the rest of the population. Dog owners in particular take more recreational walks, which improved their overall fitness levels.
But the survey also uncovered the social benefits of having a pet, saying: "Over 60 per cent of pet owners say that having a pet around when people visit makes it easier to get into conversation and create a friendly atmosphere."
So does it matter what type of pet you have? Do different pets have different health benefits? Dr McNicholas says it depends what kind of relationship you want to have with your pet.
The first is the "human" type of relationship. This is when pets provide companionship and a supportive role. Dogs or cats would fall into this category.
The second is keeping a pet for social reasons. Dog walkers always meet other dog walkers, for example.
The third relationship is when your pet is also your hobby - such as keeping exotic animals. In this category, you benefit from the calming effect of watching the animals but also gain from the social aspect of joining clubs or societies.
The health benefits of pets have become so widely accepted that many animals are now used in hospitals as part of patients' recovery programmes.
The charity Pets as Therapy (PaT) has 3,500 dogs and 90 cats currently working for them. The animals make weekly visits to nearly 5,000 hospital wards, residential care homes or special care schools in a bid to boost patients' wellbeing.
The animals may be used to help stroke victims regain the use of their limbs. "Patients want to stroke the animals so this encourages them to move their arms or hands again," says Maureen Hennis, chief executive of PaT.
Both the PaT dogs and cats are taken into care homes to provide comfort for the residents. Many of them may have given up their own pets before going into homes, so the animals help bring a sense of normality to their lives.
PaT animals also work with people suffering from depression. "They can sometimes get through the barriers these patients put up, where humans have failed in the past," says Maureen.
PaT is currently working with a psychologist from Sunderland Royal Hospital treating children with animal phobias. The results so far have been "very encouraging".
"We are enabling these children to rejoin the community," says Maureen. "They can now walk to school or go to the park when previously they were too frightened to do so."
SeeSaw, a bereavement charity set up especially for children, also uses animals to build emotional bridges.
Kathy Moore, a counsellor and project co-ordinator for Macmillan Cancer Relief, takes her dog Do-Good with her when she meets children who have a parent or sibling who is dying from a terminal illness.
Most children are unwilling to open up to a stranger, but Kathy says Do-Good helps them learn to trust her. "He can provide such a good way into my first contact with a child," she says. "Even if they are a little wary of me, most children can't resist Do-Good - he's got such a great personality and we all go on walks together."
Despite the growing body of evidence that pets are beneficial for our health, scientists have not been able to answer one crucial question - are dogs better than cats?
Dr McNicholas says it does not matter what type of pet you have, as long as it fits into your lifestyle.
"If you hate long walks but have 'bouncy' dogs that need walking, that is going to push your stress levels way up," she says. "You need to do your homework beforehand, so both you and your pet benefit from the relationship.
"Animals really can give you unconditional love. They don't care if you are having a bad hair day - you can just be yourself."Reuse content