The theory of states that organisms that are better suited for their environment will survive and reproduce

The theory of natural selection states that organisms that are better suited for their environment will survive and reproduce.

Explanation:

This theory of natural selection is proposed by the Charles Darwin. He states that nature has its own way of selection and those who survives are suited to environment. This theory is also known as the survival for the fittest.

So only the environment suited creature continues his/her journey of life and can pass its gene to future generations. It is the natural and continuous process.

the oldest known insects are believed to live around 400 millions ago as suggested by the fossil records.   some plants having woody stems also evolved during this time.

after the evolution of insects the first four legged species or the tetrapods evolved in shallow freshwater habitats from the intermediate species approximately 397 million years ago. the tetrapods went on conquering the land giving rise to amphibians, reptiles, mammals and birds.

the major split in tetrapods first occurred 340 million years ago branching off from amphibians.

363 million years ago when the carboniferous period began the insects started roaming on land and taking flights, following which the four limbed tetrapods adapted in the terrestrial habitat.