Great creative thinkers like Darwin and Gandhi have one thing in common - they had at least one elder brother or sister.

Martin Luther-King, Florence Nightingale and Thomas Jefferson too were not the first born in their families.

Man is the most competitive creature on Earth - it is this highly-tuned instinct that has helped him to become the dominant animal on the planet.

And researchers believe that the ability to compete may be most fully realised in younger children, who face a tough time jousting with older siblings for their parents' attention.

Charles Darwin: did sibling rivalry drive him on?

A study of 120,000 people concluded that the instinctive behaviour adopted by younger children to help get them noticed can stay with them for life.

And, in the case of Darwin and his ilk, it helped develop the mould-breaking creative skills that helped them make an indelible mark on society.

The essence of the human competitive instinct is examined in a BBC documentary, Human Instinct, presented by the eminent scientist Professor Robert Winston.

Before birth

In fact, the competitive instinct is so strong in humans that it manifests itself even before birth.

In the later stages of pregnancy, the mother's body is ready to give birth, and her blood pressure lowers to reduce the food supply to the baby.

However, the baby wants to continue to develop in the safety of the womb for as long as possible, so it forces its mother's blood supply back up to ensure a steady stream of nutrients.

In some cases the effect is so dramatic that the mother's life can be put at risk.

Sizing up others

Successful soldiers shared physical characteristics

As we grow up, we learn to make snap judgements about the competitive qualities of other people.

Sometimes this is based on physical characteristics alone. A prominent brow and a strong jaw line is enough to convince many people that they are up against a formidable opponent.

A study of US military cadets at the elite Westpoint Academy in 1950 found that most who went on to achieve high rank had these characteristics.

The features that make for a dominant face are no coincidence. A prominent brow and a strong jaw are signs of higher levels of the male sex hormone testosterone, and testosterone is linked to physical prowess.

Professor Winston said: "Dominant faces send an ancient signal of physical fitness, and it takes just a fraction of a second for us to make a judgement about a face.

"In that split second we work out not only if we recognise it, but we also work out how dominant it is."

Fear of losing

Nick Leeson was spurred on by fear of failure

The fear of failure is perhaps an even stronger instinct than the drive to compete.

Nick Leeson, the rogue trader whose ill-conceived dealings lost more than �800m and destroyed Barings Bank in 1995, has more experience of this feeling than most.

"As the losses increased I would take bigger and bigger risks to try to get it back.

"The walls were closing and everything was spiralling out of control - rationality was thrown out of the window.

"It was that fear of the loss of my reputation with the people who were close to me that drove what I did. I didn't want to go and expose myself to anybody, and that fear was paramount."

Human Instinct is broadcast on BBC One on Wednesday evenings at 2100 GMT.