Are you enjoying or preparing for your vacation? The summer period is a time when humans leave our usual routine, travel to find new horizons, or take refuge in more or less familiar surroundings, far from work and, if possible, to cool off from the heat. In general, we mingle with people we don't know, on the sand of the beach, in the water of the pool, or in the middle of a street full of other tourists admiring buildings in old Europe… Be that as it may, you're sure to see people holding hands: a mother or father holding their young child's hand; two little girls holding arms while laughing; a young couple gazing into each other's eyes; and also elderly couples walking side by side. And with this small gesture, they tell each other they still love each other.

If nature was the answer, what was the question? It is the quote that appears at the beginning of La respuesta (Destino), the book that paleontologist and co-director of Atapuerca Juan Luis Arsuaga has just published. It is more than 500 pages where there are some answers – let's not confuse them with certainties – and especially questions that help us to fascinatingly retrace the history of evolution and to understand ourselves, humans, in comparison with the rest of the animals.

Being able to walk upright on two legs is considered one of the most important milestones in human evolution. However, how the body adapted to this new habit was, until now, a mystery. Harvard researchers conclude that the origin lies in two changes in the pelvis, the cornerstone of vertical locomotion. More than any other part of our body, this bone structure has been radically altered over millions of years to allow our ancestors to be bipedal and roam the planet. a study published in the magazine Nature, scientists reveal the key genetic changes that reshaped the pelvis between 5 and 8 million years ago, when human ancestors diverged from African great apes.