Why do organisms of same species look similar ?

Explanation

Organisms of same species look similar because their body designs are similar. Reproduction at its most basic level will involve making copies of the blueprints of body design.
The chromosomes in the nucleus of a cell contain information for inheritance of features from parents to next generation in the form of DNA (Deoxyribo Nucleic Acid) molecules. The DNA present in the cell nucleus is the source of information for protein synthesis. The types of protein synthesised in cell are responsible for characters that are formed.
Organisms of same species have specific DNA and this DNA is inherited to next generation through reproduction. According to the information on DNA, proteins are made. So, organisms create exact copies of themselves with some variations.