Long ago, when the archaic roots of our minds were formed, people lived in small groups of 30 to 150 members, at most. Today, chimpanzees still live in groups of 30, taking care of each other.

Our ancestors, social primates, in groups of up to 150 people, could know each other. Why? First of all because they were relatives. They were connected either by blood (genes) or by marriage. And group life gave them a strong evolutionary advantage. Those who were excluded from the group had very little chance of survival on their own. Such a situation should have been avoided at all costs: “if I am excluded, I die!”

Let’s get back 500,000 years ago. We are in a group of 50-100 people. We know each other. We recognize each other. We cooperate. We hunt together. We raise our children together. We are “us”. We resemble each other (especially those who are relatives). But we are not alone – the forest / savannah is big.

There is also “they”. Who are them? They are from another group. They are strangers. Strangers are dangerous! It’s not good to deal with strangers. We can’t trust strangers. We can only trust “us”. We are able to sacrifice for “our own” (kinship altruism).

And now, let’s go back to the present. This article is about couple relationships. You may also need information from social psychology: Partners in marital relationships (or consensual unions) resemble each other in the following dimensions:

Socioeconomic status
Level of education
Personality traits

Obviously, there are always exceptions and the “resemblance” is not the same as ” identical”. But if you know couples who have been together for 20-30 years, you may have noticed such similarities. And you might think they’ve become similar over time. Not true – they were similar from the beginning! The extrovert who married a great introvert has long divorced her and so did the graduate of postgraduate courses with her ex-boyfriend who had failed to finish high school.

Why are we looking for similar ones? Why do (statistical averages) withstand partners that are similar rather than different? Why is it such a good idea to choose your life partner based on compatibility? Because we have a certain evolutionary history. Because our minds are configured in a certain way, dictated by the way endless generations of ancestors and our nature of social animals lived.

Cupid only shoots at random in movies. Men and women who start families and resist are much more similar, statistically speaking, than if they had married at random. We are still afraid of strangers and we are instinctively looking for those like us. It’s true, we no longer live in groups of no more than 150, somewhere in the savannah (how many friends do you have on Facebook?). In a single subway trip we meet more people than our ancestors throughout their whole lives. However, we prefer the one who speaks like us, thinks like us, aspires to the same holiday destinations and, let’s not forget one important thing, is part of the same social class.

We dedicate ourselves to the similar, because in the deep layers of our minds, impossible to erase, “similarity” means “members of the group” and belonging to the group means survival. Don’t look for a stronger motivation. We all want to survive! (why do you eat when you are hungry, why do you drink water when you are thirsty?)

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