First published in 1877, the book is a comprehensive overview of the scientific evidence for human evolution, from the fossil record to embryology. Haeckel was a strong advocate of Darwinian evolution, and his book was one of the most influential works on the subject in the late 19th and early 20th centuries.

The first volume of the book, Human Embryology, or Ontogeny, discusses the similarities between the embryos of humans and other animals. Haeckel argued that these similarities are evidence of a common ancestor. He also discussed the development of the human brain and nervous system, and he argued that these structures are also evidence of evolution.

The second volume of the book, Human Stem-History, or Phylogeny, discusses the fossil record of human ancestors. Haeckel described the various hominid species that have been discovered, and he argued that they provide a clear evolutionary pathway from ape to human. He also discussed the role of natural selection in shaping human evolution.

The Evolution of Man was a controversial book when it was first published. Many religious leaders objected to Haeckel's ideas about evolution, and they accused him of promoting atheism. However, the book was also praised by scientists and philosophers, and it helped to popularize the theory of evolution.

The book is still considered to be an important work on human evolution. It is a comprehensive and well-argued defense of Darwinian theory, and it provides a valuable overview of the scientific evidence for human evolution.