AsapScience explains how genetics may be to blame for a pessimistic view of the world and how this can affect your life expectancy.The Toronto-based YouTube channel explains that in one study, people with two long alleles - one form of a gene - on specific genes controlling for the "happy hormone" serotonin, were more likely to focus on positive images, such as someone enjoying an ice cream.

In contrast, those with a short allele on the same gene, were found to be more likely to focus on negative images, such as someone being robbed.The video explains that a person's outlook may also be affected by the oxytocin receptor gene. Oxytocin is often referred to as the "love hormone".

People with two copies of guanine, which is one of the four nucleobases of DNA, are more likely to be optimisitic and have higher self-esteem than those with another type of nucleobase called adenine, who are more likely to be pessimistic.

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