The Descent of Man and Selection in Relation to Sex, Vol. II (1st Edition)

In Short

This volume serves as the second half of a rigorous investigation into the mechanisms of evolution, focusing specifically on sexual selection. It explores the diverse ways males and females differ across the animal kingdom—from fish and reptiles to birds and mammals—and concludes by applying these principles to the human species. By documenting how ornamental traits, vocalizations, and combat structures emerge through the selective pressures of courtship, the inquiry provides a foundational explanation for the biological origins of beauty and behavioral divergence. Its enduring value lies in the meticulous observation of nature, offering a window into the complex, often competitive social lives of animals and the evolutionary history that humans share with the rest of the natural world.

The Story

The narrative begins with a survey of the secondary sexual characteristics in lower vertebrates. The investigation moves through the waters, where male fishes often develop vibrant colors and peculiar appendages during the breeding season, sometimes taking up the burden of nest-building and the care of offspring. In the realm of amphibians and reptiles, the patterns persist; some male tortoises show structural differences to accommodate their mates, while male alligators engage in dramatic, loud displays of strength and sound to attract females. Snakes, too, exhibit subtle sexual dimorphism, with males often bearing more pronounced color patterns.

As the focus shifts to birds, the argument expands into an exploration of extreme ornamentation. The text describes how males often possess extravagant plumes, crests, and complex vocal apparatuses designed solely for the purpose of courtship. The Argus pheasant emerges as a central example, its feathers bearing "ball-and-socket" ocelli so artistically shaded that they appear to be works of art rather than natural products. The argument posits that these features are not for survival in a hostile environment, but are the direct result of the female’s ability to appreciate and select for such refined beauty. This leads to a nuanced discussion of protective coloration, noting that while many birds—especially those that build exposed nests—evolve dull, camouflaging feathers for survival, others have evolved to maintain their brilliant colors through behavioral adaptations like nesting in crevices.

The inquiry then transitions to mammals. Here, the "law of battle" becomes more prominent, as males frequently use specialized weapons like horns and tusks to compete for access to females. The analysis of antelopes, for instance, details how seemingly impractical horns evolved into lethal tools through generations of combat. Beyond physical weapons, the text examines the role of scent, where odoriferous glands become enlarged during the breeding season, serving as chemical signals that permeate the environment.

The final arc of the volume applies these biological principles to the history and behavior of mankind. The investigation into human evolution explores how aesthetic preferences for certain features—often differing wildly across cultures—have played a role in the historical development of human traits. The narrative touches upon the social customs of various peoples, the origins of language, and the evolution of moral faculties like sympathy. It argues that the development of the human brain, with its capacity for abstraction and complex social interaction, is intimately linked to the same evolutionary pressures of selection that govern the rest of the living world. The work concludes by synthesizing these observations, framing human history as a continuation of the same natural processes that produce the splendor of a bird’s plumage or the strength of a stag’s antlers.

How It Unfolds

The aquatic and reptilian baseline The inquiry opens with a methodical look at fish, amphibians, and reptiles, identifying that sexual differences in size, color, and behavior are rarely accidental. It establishes that these traits emerge specifically during the breeding season, suggesting a direct link between physical modification and reproductive success.

The avian display The focus shifts to the complex world of birds, documenting the extraordinary lengths to which males go to attract females. Through detailed descriptions of plumage and vocal organs, it argues that these ornaments are not mere flourishes but essential tools for courtship.

The role of protection The narrative addresses the counter-pressure of survival, explaining why some species maintain dull, protective colors while others risk predation for the sake of beauty. It carefully differentiates between features developed for combat and those developed for aesthetic attraction.

The mammalian struggle The argument moves to mammals, detailing the physical armaments and scent-based signaling that define the reproductive lives of larger animals. It presents these features as the outcome of long-term selective pressures favoring specific fighting and signaling strategies.

The human connection The volume concludes by applying evolutionary logic to the human story, exploring how social behaviors, intellectual capacity, and cultural preferences have evolved over time. It links the biological origins of human traits to the same principles of sexual selection observed throughout the animal kingdom.

The People

The book relies on a vast network of observers and naturalists to build its case, turning them into the key figures of its argument. Mr. Bartlett acts as a crucial guide for understanding the behavior of exotic animals in captivity, providing accounts of how species like alligators and antelopes use their physical features during the "season of love." His observations allow the reader to move beyond theory and see the mechanical reality of how an animal’s anatomy serves its courtship needs. Mr. Bates provides essential insights into the mimicry and sexual differences of insects and birds, bridging the gap between small-scale biological variation and large-scale evolutionary change. Mr. Harrison Weir contributes vital observations regarding the social lives of pigeons, highlighting the surprising agency of the female in selecting her mate and the existence of individual preferences that defy simple instinct. Sir J. Lubbock and Mr. M'Lennan serve as points of reference for the anthropological side of the argument, helping to trace the historical and social development of human marriage customs and the practice of mate capture. Through these individuals, the reader encounters a global tapestry of life, where the scientist is not an isolated genius but a synthesizer of a thousand different observations from travelers, breeders, and scholars. Each figure, whether a seasoned naturalist or a keen-eyed observer in a zoological garden, helps strip away the mystery of nature’s diversity, leaving behind a clearer picture of how each species came to possess its unique form and function.

In Its Own Voice

Describing the extraordinary display of the Argus pheasant, the author highlights the high level of discernment required by the female:

The case of the male Argus pheasant is eminently interesting, because it affords good evidence that the most refined beauty may serve as a charm for the female, and for no other purpose.

Regarding the development of the human mind, the author connects the emergence of our higher intellectual faculties to the invention of communication:

The large size of the brain in man, in comparison with that of the lower animals, relatively to the size of their bodies, may be attributed in chief part, as Mr. Chauncey Wright has well remarked, to the early use of some simple form of language.

Commenting on the intensity of the courtship rituals observed in nature, the author captures the bizarre and aggressive displays of the alligator:

Bartram describes the male alligator as striving to win the female by splashing and roaring in the midst of a lagoon, "swollen to an extent ready to burst, with his head and tail lifted up, he spins or twirls round on the surface of the water, like an Indian chief rehearsing his feats of war."

What It's Really About

At its core, this work investigates the origin and purpose of diversity within species. It challenges the reader to consider whether the natural world is driven solely by the cold necessity of survival, or if it is also shaped by the "taste" and choice of the animals themselves. The fundamental question is one of agency: how much of an animal’s form—its colors, its songs, its weapons—is the result of the animal’s own internal preference for a mate? By tracing these preferences from the simplest creatures to humans, the book argues that beauty is not a luxury but an evolutionary force. It posits that the "secondary sexual characters" are the biological record of countless generations of choice. The text seeks to prove that the most refined, delicate, and specialized traits in nature are the direct consequence of a long-standing, active engagement between the sexes, fundamentally linking the survival of the species to the aesthetic life of the individual.

Why Read It Today

Readers who enjoy the slow, deliberate process of scientific discovery will find this book deeply rewarding. It is not a quick read; it is a dense, patient, and highly specific account that values a single feather pattern or a unique vocal organ as much as a broad theoretical claim. You will find yourself immersed in a world of nineteenth-century observation, where the writing reflects the period’s earnest, sometimes colonial, attitudes toward "savage" peoples and animals alike. These perspectives are a product of the time, and modern readers may find the language regarding human cultures to be dated or problematic. However, the core of the book—the observational rigor—remains impressive. It feels like walking through a vast, dusty, and wonder-filled museum with a guide who refuses to leave any stone unturned. You will come away with a profound sense of the continuity between the human experience and the natural world. It invites you to look at a peacock’s tail or the song of a bird and see not just a pretty sight or sound, but the result of a long, complex, and fascinating evolutionary dialogue. The book is for those who want to understand the why of nature, and who possess the patience to follow a master observer through the labyrinthine details of the living world. It is a work that demands your attention, but in return, it fundamentally changes how you perceive the living creatures you encounter every day.