Each child after the first born is slightly less bright as they have to 'share' parents, revealed a new study by the Leipzig University in Germany.
Scientists also suggest that having your parents' undivided attention means you end up learning more, which benefits the eldest child. However, in a two-child family the eldest won't necessarily dominate. They have a six in ten chance of a higher IQ, so their younger relatives still have a strong chance of overtaking them.
As well as demonstrating a heightened intelligence, older children also displayed an increased perception of their brain power.