Herbert Spencer, a 19th-century sociologist and philosopher, is well-known for his theory of social evolution, which he applied to both biological and social phenomena. His theory drew inspiration from Charles Darwin's theory of biological evolution and aimed to explain the development and progress of societies over time. Spencer's ideas are often associated with Social Darwinism, a concept that applied the principles of natural selection to human societies. Here are the key components of Spencer's theory of social evolution:

1. Organic Analogy: Spencer employed an organic analogy to explain social evolution. He likened society to a living organism, suggesting that societies, like living organisms, evolve from simple to complex forms. According to Spencer, societies, like organisms, have various parts that function together to maintain the whole.
2. Principles of Evolution: Spencer applied the principles of evolution, particularly natural selection, to social development. He argued that societies evolve in a manner similar to biological organisms. Social institutions and practices that contribute to the survival and well-being of the society are naturally selected and passed on to future generations, while those that hinder progress are eliminated.
3. Differentiation: One of Spencer's key ideas was the concept of differentiation. He proposed that as societies evolve, they become more complex and specialized. Differentiation refers to the increasing division of labor and the emergence of specialized institutions within a society. According to Spencer, this specialization contributes to the overall efficiency and functionality of the social organism.
4. Integration: While societies differentiate, Spencer also emphasized the importance of integration. Integration refers to the coordination and interdependence of specialized parts within a society. Spencer believed that for a society to function effectively, there must be a balance and integration among its various components.
5. Progressive Development: Spencer believed in the inherent progress of societies over time. He argued that, like biological evolution, social evolution leads to increased complexity, efficiency, and progress. However, he did not view progress as linear but rather as a gradual and adaptive process.
6. Laissez-Faire and Limited Intervention: Spencer was an advocate of laissez-faire capitalism and limited government intervention. He believed that societies should evolve naturally, and interference from external forces, including the government, could disrupt the natural process of evolution. This perspective aligned with his broader philosophy of individualism and free-market capitalism.
7. Criticism: Spencer's theory of social evolution, particularly his application of Darwinian principles to society, has faced criticism for being overly simplistic and deterministic. Critics argue that it oversimplifies the complexities of human societies and fails to account for cultural factors, historical contingencies, and the role of human agency in social change.

In summary, Herbert Spencer's theory of social evolution was a significant contribution to the field of sociology during the 19th century. While his ideas were influential in shaping early sociological thought, they have been criticized for their oversimplification and deterministic outlook. Despite the criticisms, Spencer's work laid the groundwork for later sociologists to build upon and refine theories of social change and evolution.