Are your traits equally passed on to each child or would your first child contain more direct features of you then, say your third?
-A curious adult at The Tech
February 4, 2010
Your first or third child may be more like you than your other children. But this is mostly due to chance. Birth order doesn't necessarily favor either parent.
This isn't to say that birth order has no effect. Brothers and sisters can be different based on the order in which they were born. It just doesn't have anything to do with the traits that you pass down to them.
Many of the traits you pass on to your children come from the DNA that you give them. But the particular DNA they get from you is random. And remember, half of their DNA comes from you, and half from the other parent.
There are, of course, certain combinations of you and your partner's genes that will favor you. But those particular combinations don't come up at a certain time. It is just by simple random chance. (Click here to learn more about how parents pass their DNA onto their children.)
This means that it is almost all due to chance whether your firstborn or your third child looks and acts more like you. In fact, it may be that whether a child is more or less like you has more to do with your own birth order.
Birth order has more to do with the environment in which the child develops, both inside the womb and after they are born. So if you're a third born, then your third born child might have more of your qualities. Not because of DNA but because of the environment where you both developed and were raised.
This is the classic "nature versus nurture" debate. We'll get back to this later, but first, let's talk about a couple examples in which birth order does affect traits.
Traits Affected by Birth Order
Many traits have been shown to be affected by birth order. Some have to do with different environments in the womb. And some with different family environments.
For example, a child is more likely to be left-handed if he or she has several older siblings. And having many older brothers increases the chances that a boy will be gay.
Both of these are thought to come from changes in the mother's body that affect how her child develops. Men and women have some differences in hormones and proteins. So a mother's body would be seeing some new hormones and proteins when her son is developing in her body.
Our bodies are designed to attack foreign things (since diseases usually come from foreign bacteria or viruses). So when a mother's body sees foreign male hormones and proteins, it might try to attack them.
And after having multiple male children, this begins to have an effect on the child. The mother's body gets stronger at attacking the male hormones and this could change the child's sexual orientation.
Other birth order traits seem to have more to do with the family environment. A first born is born into a very different family compared with a third or fourth child.
The oldest child is an only child for at least nine months. They tend to get more parental attention and involvement. Because they are the oldest children, they also take on the responsibilities of tutoring and helping their younger siblings. And these sorts of things sometimes seem to give the first child a bit of an IQ boost (3 points according to one study) and a bit more height.
First born children tend to get more responsibilities. They had to help raise their younger siblings. So they grow up faster and seek stable jobs and lives. Meanwhile, youngest children tend to grow up always getting doted upon and getting their own way. This makes them more likely to be rebellious and creative.
Nature versus Nurture
There are two things that influence the development of a person. They are nature and nurture.
Nature refers to the genes that we are born with. Nurture on the other hand means the environment in which we are raised. Scientists now agree that most of our traits are determined by the mix of nature and nurture.
One way that scientists study the effect of the environment is to look at identical twins. Twins share exactly the same DNA because they come from one fertilized egg that split into two. So the environment accounts for almost all the differences between them.
If you know any identical twins, you already know that they are not the same person. Identical DNA doesn't mean they have to be the same. They might differ in personalities, likes and dislikes, and reactions to situations. Even their fingerprints are different!
And scientists have discovered some interesting traits that are controlled by genes. That means twins, even those raised in separate families, are more likely to share the traits.
For instance, if one twin has an eating disorder, it is more likely that the other twin will have it too. And depression also seems to have some genetic influences.
So both our genes and our environment shape who we are. And you may be more like one of your children for either reason.
It could be that that child happened to get a set of genes that caused them to look or act more like you than your partner. This wouldn't be caused by birth order. It is just random chance.
But it could also be because you share the same birth order as that child. Maybe you were both firstborn children. Or maybe you were both the babies of the family. In this case, birth order matters. But it has nothing to do with the traits that you passed on. It is just the environment that the two of you happened to grow up in.