People all over the world react similarly when they are reunited with loved ones. for example, if you watch people greeting each other at family reunions, they tend to have the same joyful expressions on their faces, no matter what country they come from. this similarity can be attributed to: our family upbringing being so similar. our cultures being so similar. our shared human genome. random errors in gene replication.

The similarity in expressions and reactions when people are reunited with loved ones all over the world can most accurately be attributed to "our shared human genome." Humans, regardless of culture or location, have inherent emotional responses that are deeply embedded in our biology. These reactions are part of what makes us human and are influenced by the universal human genome that dictates certain behaviors and expressions, such as joy and affection when seeing family and friends after a period of separation. Universal expressions of emotion suggest that there are biological foundations for the way humans express emotions, which transcend cultural boundaries.

Extra: The concept being referred to here is the idea of biological universals, meaning that all humans share certain traits, which are part of our genetic makeup. This falls into the study of evolutionary psychology and the understanding of how certain behaviors or emotional responses have been advantageous for survival and therefore preserved throughout human evolution.

The study of facial expressions and emotions often points to the work of psychologists such as Paul Ekman, who identified a set of basic emotions and corresponding facial expressions that appear to be universally recognized. These include happiness, sadness, fear, disgust, surprise, and anger. Such emotions and reactions are not learned but are innate and can be observed across different cultures, suggesting that they are embedded in our genetic code rather than being solely products of our environment or individual upbringing.

On the subject of "random errors in gene replication" (mutations), while they are a fundamental mechanism of evolution and can lead to differences among individuals and populations over long time periods, they do not explain the common emotional responses observed across all humans when seeing loved ones. Cultures around the world can vary greatly in practices, traditions, and social norms, so the similarity of emotional expression is not likely due to "our cultures being so similar." Similarly, "our family upbringing being so similar" does not account for the universal nature of these expressions, as family upbringings can differ dramatically from one household to another.