Ok, I submit the following observations for your verification via the scientific method.
Observation 1: Some individuals within a population survive and produce offspring better than other individuals in that same population.
Observation 2: Capabilities of individuals (speed, camouflage, resistance to disease, beak size and strength..etc) differ between individuals in a population.
Observation 3: The differences in capabilities in individuals in a population cause differences in survival ability and offspring production.
Observation 4: Offspring of individuals are more likely to have capabilities on the level of their parents rather than capabilities on the level of other individuals within the same population.