Middle child syndrome is a myth and siblings play only a small part in our development, a study has found.
It has long been thought that middle children are excluded and ignored, or even totally neglected, as a result of being born in between their siblings.
However, the new research by academics at the University of Leipzig says that this "does not play a major role" in shaping a personality.
The study also found that the idea that a girl is more likely to be a tomboy if she has lots of brothers, is not borne out by the data, and that the gender of our siblings has little impact.
The researchers analysed data on more than 80,000 adults from nine countries including the US, Germany, Mexico and China.
Data was collected from longitudinal studies which gather information about people's lives, including their living conditions and personality traits, over decades.
The German team found there was no link between personality traits such as risk-taking, emotional stability, conscientiousness and patience, and sibling gender.
Study author Dr Julia Rohrer from the University of Leipzig said: "Our findings refute the idea that growing up with brothers or sisters causes us to develop certain personality traits in the long term that are considered 'typically female' or 'typically male' in a society.
"Overall, current research suggests that siblings have a surprisingly small impact on personality in adulthood.
"For example, previous studies by our research group show that sibling position - that is, whether a person is a firstborn or a sandwich child, for example - also does not play a major role in personality."
The team say sibling gender can affect other areas of your life, for example, earlier studies have shown women with brothers earn less than those with sisters or no siblings.
However siblings only play a very small role in shaping your personality as an adult.
Dr Rohrer added: "There do seem to be some interesting dynamics here that are related to gender, but personality is probably not part of the explanation for such effects."
The findings were published in the journal Psychological Science.
