Humans are rational beings. We have the capacity to identify relevant information for decision-making; to evaluate different pieces of information and choose the one we consider most reliable; and, when faced with contradictory clues or evidence, we can weigh them to ultimately choose the best option.

Before Yuri Gagarin became the first man in space, plenty of creatures orbited above human heads. During the 1950s, the Soviets and Americans took their rivalry beyond our planet, starting a space race that would immortalize names like Gagarin, Neil Armstrong, Aleksei Leonov, Buzz Aldrin, and Valentina Tereshkova. But before them, there were Laika, Baker, Belka, Ham, and Strelka. The first animals in space, but not the first to fly, since in 1783 the Montgolfier brothers had placed a sheep, a duck, and a rooster inside a hot-air balloon to see what would happen if they flew.

For decades, the ability to combine words to create new meanings, a characteristic of human language called compositionality in linguistics, has been considered exclusive to humans. For example, the word biology It is formed by morphemes bio-, which means life, and -lodge, which means study or science. Biology is, therefore, the study or science of life. The other, as for example when we say "good soccer player" or "attentive teacher."

Since ancient times, humans have wondered what makes us human. Different disciplines have sought answers to this endless question, and surely one of the most enticing proposals comes from biology, particularly genetics. Comparative biology is, in this sense, a very powerful tool that allows us not only to quantify the differences between species, but also to understand how these differences may have contributed to specific traits in our lineage. By comparing human genomes with closely related species with which we share a recent common origin, such as the great apes, we can identify which molecular changes are unique to humans and which we share with other primates. This evolutionary perspective helps us distinguish which traits are truly human and which are part of a deeper common heritage.