The modifications that appear in organisms appear at random. Most of these changes are detrimental. Once in a while a modification to a member of a species gives it an advantage in survival over its rivals. These traits will be selected for in the population in breeding.
Viruses and bacteria, with simpler DNA sequences than multicellular organisms can mutate more easily and be modified faster. I wonder how many who still don't believe in Darwin's theory also believe that the Corona Virus was created by a sinister scientist in Wuhan China. How many of these are also hesitant to be vaccinated? As the vaccine has become more available, the 7day average for new full vaccinations has been coming down from 891.1 per day on April 18 to 332.3 per day today.