What is the essence of the doctrine of the evolution of the living world on Earth?

There are 3 factors of evolution: variability, heredity, selection. For various reasons, living organisms experience disruptions in the genetic program, which manifest themselves in various deviations. This is mutability.
These deviations are inherited by descendants, since they are fixed in the genome. This is heredity.

If the changes that have arisen contribute to the improvement of the organism’s viability in these conditions, it develops well and gives birth to offspring. If the deviations are harmful – the body withers and dies – and either does not give offspring, or it is not viable. As a result, after many generations those individuals who have proved to be more adapted will survive. This is selection. As a result of this selection, the species as a whole changes, improves, becomes more complex, and in several directions. This is evolution. Thousands of years later, in this way, new species appear, unlike their ancestors. The more the conditions of their existence have changed during this time, the more differences they have.