We must start from an assumption: one of the characteristics of living beings is that of being endowed with a project. Within this project a powerful mechanism is that of natural selection. And it is here that accidental alterations occur, that is due to chance, which can alter the sequences of the genome, of the DNA, on which the selection acts. In fact, a random modification of the DNA will then be passed down in millions and millions of copies.

It is extraordinary that these same concepts were synthetically formulated by Democritus who lived between 460 and 370 BC. We must not confuse chance with probability. Chance is an episode, a unique and unrepeatable event, probability is a repeatable and measurable event whose frequencies are known. Playing poker the chance of having three cards with the same sign is 1/46, while winning the Italy lottery prize is 1 for the number of tickets issued.

Jaques Monod and Francois Jacob were two French scientists who in 1965 were awarded the Nobel Prize in Medicine for the research of the mechanisms that regulate DNA. In particular, their message was that “we are the fruit of chance and of the need to preserve our life project”. But how will we be able to experimentally verify these concepts, or if life on earth were to start again it would be the same as we know it today? In addition to researchers from an international team, biologists from the University of Pisa participated in the study. The study was published in Nature Ecology and Evolution. The means was to find an evolutionary process that appears to have repeated itself repeatedly and independently in nature. The study aimed to understand if evolutionary events always happen in the same way starting from extraordinarily similar assumptions. The answer was no, because the system evolves continuously, but in largely random and different ways.

The study of DNA highlights and confirms the unpredictability of evolution. In the book "A Series of Lucky Events" Sean Carroll, evolutionary biologist and professor of molecular and genetic biology at the University of Wisconsin-Madison, tries, with concrete examples, to answer these questions. The Chicxulub Crater in Mexico is an ancient impact crater. It dates back to about 65.95 million years ago. It is estimated that the diameter of the meteorite was between 10 and 14 km. The mass extinction of dinosaurs allowed mammals to develop and, ultimately, homo to evolve. Carroll defines it as "the most unlikely event that allowed us to exist," because it would not have been possible if the asteroid had not fallen between Mexico and the Atlantic Ocean.