Discuss the theory of the evolution of life forms.

(A) Conventional religious literature tells us about the theory of special creation. This theory has three connotations:
$1$. All living organisms (species or types) that we see today were created as such.
$2$. The diversity was always the same since creation and will remain the same in the future.
$3$. The Earth is about $4000$ years old.
All these ideas were strongly challenged during the $19$th century. These conclusions were based on observations made by Charles Darwin during his sea voyage in a sail ship called $HMS$ Beagle.
He concluded that existing living forms share similarities not only among themselves but also with life forms that existed millions of years ago. Many of these life forms do not exist anymore. There had been extinctions of different life forms in the years gone by,just as new forms of life arose at different periods of history of Earth.
Life forms evolved gradually. Any population has built-in variation in characteristics. Those characteristics which enable some to survive better in natural conditions (climate,food,physical factors,etc.) would outbreed others that are less-endowed to survive under such natural conditions.
Another word used for fitness of individuals or populations is that those who are better fit in an environment,leave more progeny. Darwinian fitness is ultimately and only a reproductive fitness. Hence,those who are better fit in an environment,leave more progeny than others.
These,therefore,will survive more and hence are selected by nature. He called it natural selection and implied it as a mechanism of evolution. Let us also remember that Alfred Wallace,a naturalist who worked in the Malay Archipelago,had also come to similar conclusions around the same time.
As time passed,new forms of life arose. All existing life forms share similarities and share common ancestors. However,these ancestors were present at different periods in the history of Earth (epochs,periods,and eras). The geological history of Earth closely correlates with the biological history of Earth. The common conclusion is that Earth is very old,not thousand of years as was thought earlier,but billions of years old.