Natural selection is based on Darwin's observation that individuals most likely to survive and reproduce are those

that descended from previous life forms

with traits best suited to their current environment

with many offspring that have similar traits

that do not resemble their ancestors

with traits best suited to their current environment

Explanation:

Natural selection proposes that nature selects those organisms that are well adapted to the prevailing environmental conditions to survive and reach reproductive maturity with the favourable characteristics being passed on to the offspring. Those organisms that are poorly adapted die leaving no offspring and their traits are eventually eliminated.