But where did the the birth-order theory actually come from, and is there any truth to it?

Read on for more on birth-order theory.

Where did birth-order theory come from?

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Photo: Claudette Barius/HBO

Whats the birth-order theory conception of an oldest child?

What about a middle child?

(Fun celebrity fact:Bella Hadidis a middle child!)

And a youngest child?

(Amy Marchburning her older sister Jos manuscript inLittle Women?

Why is birth-order theory suddenly everywhere?

Elsewhere, users like@t0nit0nehave broken down the compatibility of different birth-order pairings.

(Hint: Its better to be a firstborn involved with a lastborn than a firstborn with another firstborn.

Youve been warned!)