It's debatable, really. but, it is said that the earth was created by "the big bang theory" which is when a huge explosion occurred over 12 billion years ago. humans are said to be created through the process of evolution. started as apes 5 million years ago, and over time the apes improved by natural selection, and boom, here we are :)
The answer is mutation
of genes. The mutations were beneficial and gave the individuals of the population
advantage and hence increased their survival. The classic features of birds
evolved one by one and gave birds advantage over their dinosaurs counterparts, especially the feature of small size.
