A study by Harvard University researchers examined birthing records of 58,007 women and found that families with at least three children show a tendency toward having boys or girls rather than a simple 50/50 chance. In families with two girls, the probability of a third girl increases, as does the probability of a boy following two boys. The study suggests age at first birth may influence this tendency, indicating that family composition and underlying biology may affect sex determination in offspring.
The study found that instead of straight 50/50 odds between boys and girls with each birth, families with at least three children tend to follow a 'weighted coin toss.'
If the first two children born in a family are girls, the chances of the third child being a girl are higher than for a boy. The same is true for families with boys.
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