In the following excerpt, Slosson presents a wide-ranging biographical sketch of Haeckel, by turns laudatory and critical, which views his work and thought in the context of his personal life.

In the following excerpt, Gillis critiques Haeckel's Monism and his presentation of it, treating the former as a variety of religious dogma and the latter as an often dishonest attempt to make facts conform to theory.

In the following excerpt, Thomas and Thomas offer an account of Haeckel's professional and personal life .

In the following excerpt, Harris offers his personal recollections of an encounter with Haeckel, as well as a chance meeting with the latter's translator.

In the following essay, Gauss combines a review of Last Words on Evolution with an assessment of Haeckel's career.

In the following review of The Evolution of Man, Voorhees offers a positive appraisal of the work, in spite of what he considers Haeckel's penchant for digression and speculation.

In the following review of The Evolution of Man, Pycraft presents Haeckel's work as a complement to that of Darwin and Huxley.

In the following review of The Evolution of Man, a critic faults Haeckel for making broad and often unsubstantiated claims.

In the following review of The Story of the Development of a Youth, Smertenko considers the book as a key to understanding the later Haeckel.

In the following review of The Wonders of Life, Cockerell critiques Haeckel's account of man's origins, and treats Monism as a form of religious faith.

In the following essay, a critic assesses Systematische Phylogenie.