A Critical Examination of Mr. Darwin’s Work, “On the Origin of Species,” Informative Summary


This lecture, delivered in 1863, presents Thomas H. Huxley’s critical analysis of Charles Darwin’s landmark work, “On the Origin of Species.” Huxley focuses on Darwin’s hypothesis that the phenomena of organic nature arise from the interplay between the inherent properties of organic matter (atavism and variability) and the conditions of existence. He meticulously examines the validity of this hypothesis, employing a rigorous scientific framework of testing and evidence.

Huxley argues that Darwin’s theory offers a compelling explanation for the majority of observed phenomena, particularly those related to structural similarities and differences among species and the presence of rudimentary organs. He supports this claim with evidence from comparative anatomy, classification systems, and the fossil record, demonstrating the coherence of Darwin’s hypothesis with the observed patterns of evolution. However, Huxley also acknowledges a significant challenge to Darwin’s theory: the phenomenon of hybrid sterility. He points out that Darwin’s theory, as it stands, cannot fully explain the inability of some species to produce fertile offspring when crossed.

Key Findings:

  • Darwin’s theory provides a powerful explanation for the observed phenomena of organic nature, particularly structural similarities and differences among species.
  • Rudimentary organs are easily explained by Darwin’s theory of descent with modification.
  • The fossil record strongly supports the idea of gradual modification over time, aligning with Darwin’s hypothesis.
  • Darwin’s hypothesis is particularly well-suited to explain the persistence of certain types of organisms over long periods, known as “persistent types.”
  • Darwin’s theory faces a significant challenge in explaining the phenomenon of hybrid sterility.
  • While Darwin’s hypothesis is the most compelling explanation currently available for the origin and diversification of life, it must be tested rigorously.


  • Understanding Scientific Inquiry: This lecture exemplifies the process of scientific inquiry, including the formulation of hypotheses, the importance of evidence, and the need for constant testing and refinement of theories.
  • Atavism and Variability: The lecture introduces the concepts of atavism (the tendency to revert to ancestral traits) and variability (the tendency to deviate from ancestral traits), highlighting their crucial roles in the process of evolution.
  • Conditions of Existence: Huxley emphasizes the importance of environmental factors in shaping the course of evolution. This concept of “conditions of existence” highlights the dynamic interplay between organisms and their surroundings.
  • Rudimentary Organs: The lecture explains how rudimentary organs, structures that appear to serve no purpose, are powerful evidence for the idea of common descent and modification. These seemingly useless organs are interpreted as remnants of functional structures present in ancestral organisms.
  • Hybrid Sterility: The lecture delves into the phenomenon of hybrid sterility, a significant challenge to Darwin’s theory. Huxley points out that Darwin’s theory, as it currently stands, cannot fully account for this observation.
  • Evolutionary History: This lecture sheds light on the vast timescale of evolutionary history, demonstrating how the fossil record provides a glimpse into the past and supports the idea of gradual change over millions of years.
  • Importance of Evidence: Huxley emphasizes the centrality of evidence in scientific inquiry, demonstrating the need for careful observation, data collection, and rigorous analysis to support or refute scientific hypotheses.

Historical Context:

This lecture was delivered in 1863, a time of intense debate and controversy surrounding Darwin’s revolutionary theory of evolution. Huxley, a staunch supporter of Darwin’s views, was actively engaged in public debates and discussions about the implications of Darwin’s ideas for understanding the natural world and the place of humanity within it. The publication of “On the Origin of Species” in 1859 had sent shockwaves through the scientific community, challenging the prevailing view of creation and sparking a vigorous exchange of ideas and arguments.


  • Organic matter has inherent properties of atavism and variability: This means that organisms tend to resemble their ancestors but also have the capacity to deviate from those traits.
  • Conditions of existence play a key role in shaping the evolution of species: Environmental factors, such as food availability, climate, and predation, influence which traits are favored and passed on to future generations.
  • Rudimentary organs, like the splint bones in the horse’s leg, are remnants of functional structures present in ancestors: These structures have lost their original function due to evolutionary changes, providing evidence of common descent.
  • The fossil record reveals a gradual succession of life forms over time: Fossil evidence indicates that organisms have changed over millions of years, supporting the idea of evolutionary change.
  • The persistence of certain types of organisms over long periods is a phenomenon known as “persistent types”: This observation suggests that some groups have remained remarkably stable while other organisms around them have undergone significant changes.
  • Hybrid sterility, the inability of some species to produce fertile offspring when crossed, is a challenge to Darwin’s theory: This phenomenon remains unexplained by Darwin’s theory and requires further investigation.
  • Darwin’s theory is the most compelling explanation for the diversification of life currently available: It offers a scientific framework for understanding the interconnectedness and relatedness of all life forms.
  • Species are constantly evolving and adapting to their environments: This is an ongoing process driven by the interplay of atavism, variability, and conditions of existence.
  • The structural differences between humans and other primates are not as significant as previously believed: This undermines the argument that humans are fundamentally different from other animals, supporting the idea that humans are part of the same evolutionary lineage.
  • Human intelligence and language are powerful adaptations that have enabled the success of our species: These traits have allowed humans to record and transmit knowledge, accelerating cultural and technological development.
  • The relationship between structure and function is not always directly proportional: Minute changes in structure can have profound effects on function, as illustrated by the example of a watch.
  • The capacity for language is a defining characteristic of human intelligence: It enables communication, collaboration, and the transmission of knowledge across generations.
  • Variations in the nervous system can have significant effects on behavior and function: Slight changes in nerve activity can lead to major changes in abilities, such as speech.
  • Darwin’s work is considered a landmark contribution to biological science: It has revolutionized our understanding of life and has provided a foundation for modern biological research.
  • The “Origin of Species” is a complex and nuanced work that requires careful and repeated reading: Its depth and richness of detail make it a rewarding but challenging read.


  • Sixty to seventy thousand feet of stratified rock provide a record of an enormous amount of time: This geological record allows scientists to trace the history of life and evolution.
  • The horse has only one “finger” in its forefoot and one “toe” in its hind foot: This is a result of evolutionary adaptation, with the loss of toes being a key feature of horse evolution.
  • The whalebone whale has horny “whalebone” plates in its mouth and no teeth, while the young foetal whale has teeth that never develop: This indicates a transition from toothed ancestors to a toothless, whalebone-based feeding strategy.
  • The newest tertiary deposits contain the remains of creatures closely allied to those that live in the same areas today: This supports the idea of gradual evolution and continuity in life forms.
  • The ‘Megatherium’ (a giant sloth) and ‘Glyptodon’ (a giant armadillo) were found in South American newest tertiary deposits: These fossils provide evidence for the evolution of unique and specialized animals in South America.
  • The types of animals found in the newest tertiary deposits of Australia resemble those found there today: This demonstrates the consistency of evolutionary patterns across different continents.
  • The type of construction of certain fish families has persisted from the Carboniferous period right up to the Cretaceous period: This highlights the ability of some groups to remain remarkably stable over long evolutionary timescales.


  • Atavism: The tendency of an organism to exhibit traits of its ancestors.
  • Variability: The tendency of an organism to deviate from its ancestral traits.
  • Conditions of Existence: The environmental factors that influence the survival and reproduction of organisms, including climate, food availability, and predation.
  • Rudimentary Organs: Structures that appear to have no function in an organism, often interpreted as remnants of functional structures in ancestors.
  • Hybrid Sterility: The inability of some species to produce fertile offspring when crossed with other species.
  • Species: A group of organisms that can interbreed and produce fertile offspring.
  • Genus: A taxonomic category that groups together closely related species.
  • Palaeontology: The study of fossils.
  • Fauna: The animal life of a particular region or period.
  • Flora: The plant life of a particular region or period.


  • Pigeons: Huxley uses the example of domestic pigeons to demonstrate how selective breeding can create distinct varieties within a single species, supporting the idea that natural selection can drive the evolution of new species.
  • Horse: The example of the horse highlights the concept of rudimentary organs, demonstrating how the splint bones in the horse’s leg represent remnants of toes that were present in its ancestors.
  • Whalebone Whale: The whalebone whale exemplifies the process of adaptation, where a change in feeding strategy (from teeth to whalebone) has resulted in the loss of functional teeth in the adult form.
  • Sheep and Cow: The sheep and cow illustrate the phenomenon of atavism, with the presence of rudimentary teeth in calves indicating a past evolutionary history where these structures were functional.
  • Pig: The pig provides a comparison to ruminants, demonstrating that closely related animals may retain features that have been lost in other lineages.
  • Rhinoceros: The rhinoceros further demonstrates the concept of rudimentary organs, exhibiting well-developed toes that are absent or vestigial in its close relative, the horse.
  • English and Greek Languages: The shared roots between English and Greek languages are used as an analogy to explain the structural similarities between different species, indicating a common evolutionary origin.
  • Watch: The example of a watch highlights how minute changes in structure can have profound effects on function, illustrating the potential for significant functional divergence even with subtle structural differences.
  • Human Speech: Huxley uses the example of human speech to emphasize how a seemingly simple functional difference, such as the ability to communicate through language, can have vast and far-reaching consequences for intelligence and social behavior.
  • Fossil Succession: The example of the succession of different animal and plant fossils across geological strata demonstrates the gradual change in life forms over time, consistent with Darwin’s theory of evolution.


Thomas H. Huxley’s critical examination of Darwin’s “On the Origin of Species” underscores the revolutionary nature of Darwin’s ideas and their enduring relevance to understanding the history and diversity of life. While acknowledging the challenges presented by hybrid sterility, Huxley argues that Darwin’s hypothesis offers the most compelling explanation currently available for the origin and diversification of life. He emphasizes the importance of rigorous scientific inquiry, the centrality of evidence, and the need for constant testing and refinement of scientific theories. This lecture provides a valuable insight into the scientific debate surrounding Darwin’s ideas and the ongoing quest to unravel the mysteries of the natural world.

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