Step 1: Understand locus standi.
The old rule of locus standi meant only the person whose own rights were hurt could go to court. This blocked the poor and weak, who often could not approach the court themselves.
Step 2: What the Supreme Court did.
The Court gradually relaxed this strict rule. It allowed public-spirited people to file petitions on behalf of others who could not come to court for the enforcement of their fundamental rights.
Step 3: Name the development.
This relaxation is the foundation of Public Interest Litigation (PIL). The focus shifted from who is standing before the court to what public wrong needs to be corrected.
Step 4: Recall the case background.
Starting in the 1980s, cases like S.P. Gupta v. Union of India recognised that a public-minded person can move the court for those unable to do so. This is the hallmark of PIL.
Step 5: Eliminate the wrong options.
Individual petitions alone is the opposite of what happened. Judicial review of administrative action and the expansion of Article 226 writ jurisdiction are related ideas but do not capture the specific relaxation of locus standi, which is the heart of PIL.
Step 6: Conclude.
This development is most closely associated with the evolution of Public Interest Litigation.
\[ \boxed{\text{The evolution of Public Interest Litigation.}} \]