Buzz
The overarching principle of natural selection has never adhered to human moral standards or aesthetic preferences. As nature evolves, it takes shortcuts and reacts to selection pressures, often producing results that can appear shockingly brutal or intentionally cruel from a human perspective. The diversity and complexity of life on Earth are astonishing and strange, but they aren't always kind or gentle.
10. Traumatic Insemination
A particularly brutal manifestation of sexual selection is the fierce morphological battle between males and females to develop genitalia that maximize reproductive success during mating. This process is so prevalent that penises are considered the fastest-evolving organs in species with internal fertilization and are often indicators of new speciation events.
In certain male invertebrate species, this leads to the evolution of cruel penises adorned with barbs and spines that are intended to injure the female's reproductive system, reducing her chances of mating with other males.
The process is taken to grotesque extremes in bedbugs (Cimex lectularius), where the male's penis has evolved into a brutal spike used to impale the female in the abdomen, bypassing her reproductive tract entirely. This results in painful sexual injuries for the female, who suffers from a reduced life expectancy due to the energy required to heal and the increased vulnerability to diseases.
9. Backup Offspring
Life in the wild is unforgiving, and natural selection impacts animals from their very first moments. In a grim cost-benefit calculation, certain large bird species, including some pelicans (Pelicanus sp.) and crested penguins (Eudyptes sp.), offset the substantial investment required to raise a healthy chick by laying a second, smaller egg. This 'B-chick' is destined to die shortly after hatching.
Smaller and weaker than its elder sibling, the B-chick is in direct competition for the parents' attention and resources. It can expect a short, unfortunate life of neglect and hunger, often being pecked to death or cast out of the nest within its first week. The sole purpose of the B-chick is to act as a backup, in case the favored older sibling dies. It serves as a living insurance policy for the parents' investment in raising offspring.
For many species with large broods in confined spaces, such as frogs and spiders, sibling cannibalism is a constant threat. Although hungry young animals would prefer not to consume their brothers and sisters if given the choice of another victim, many will do so without hesitation.
8. Paedomorphosis
One way for a species to undergo rapid morphological change is to reverse the genetic clock, adjusting the pace at which traits develop during early stages of life. This process blurs the line between adults and embryos, transforming infants into stealthy, agile creatures, while adults become soft, vulnerable beings.
Male marine iguanas (Amblyrhynchus cristatus) employ a related tactic as an alternative mating strategy. In an effort to increase reproductive success while avoiding the strenuous task of establishing and guarding a large territory with a harem of females, some males choose not to mature. These 'sneaker' males forgo developing prominent secondary sexual traits, instead maintaining a juvenile appearance similar to females.
Sneaker males, however, are secretly sexually active. Research indicates they begin by discreetly engaging in masturbation within the harem, before swiftly attacking an unsuspecting female and ejaculating inside her, performing a covert copulation right under the territorial male's oblivious gaze.
Even more disturbing is the reproductive behavior of certain insects, including some bagworm moths (Psychidae). While the males of these species are typical, the female caterpillar never emerges from her pupa, instead remaining in a fetal, wormlike state within a protective bag, though with fully developed adult genitalia. The male mates with her by inserting his prehensile, extended abdomen through her casing, often dying as he becomes trapped.
A final, intriguing thought on this subject is that our own species is also paedomorphic. Over the course of our mammalian evolution, our faces have regressed and flattened to appear more childlike, a trait that has been accentuated by the subtle morphological differences between adult human males and females.
7. Animal Sessility
A common form of zoological regression is sessility. Sessile animals forsake an active, free-moving lifestyle for a stationary, vegetative one, remaining permanently attached to a surface. Barnacles (Cirripedia), a group of crustaceans related to shrimps and crabs, begin their lives as free-swimming creatures called cyprids. Once they find a suitable location, they attach themselves upside down using secretions from their antennae, gradually degenerating into immobile, filter-feeding cones, losing their eyes, antennae, and structural integrity, eventually transforming into flexible bags that develop a hard, calcareous shell.
A similar process occurs on land in the sooty beech scale insect (Ultracoelostoma assimile) of New Zealand’s South Island, where the crawling female larva embeds herself in tree bark. Her legs and antennae wither away, and her body morphs into a bloated, spherical mass. Sessility might seem like a step backward, but it actually offers safety. This adaptation enabled Precambrian animals to attach to and control the uneven and unstable ocean floor, forming tightly bonded, mutually beneficial communities.
Think of sessility as the moment when a morbidly obese man decides it’s easier to stop struggling to get up from his armchair and instead remain seated. Uncomfortably, it’s a strategy that has repeatedly proven successful in nature.
6. Sexual Parasitism
How stable is the relationship between the sexes? Nature offers many exceptions, some of which are far from pleasant. In a world filled with infidelity and promiscuity, where reproductive success is paramount, some species have evolved males willing to go to extreme lengths to father offspring.
In 23 out of the 160 known species of deep-sea anglerfish, tiny males have a single purpose in life: to locate one of the enormous, grotesque females of their species and latch onto her body using their jaws. These males lack functional mouths or digestive systems, meaning they will starve to death within months unless they successfully mate.
Once attached, the male’s body begins to deteriorate and lose all form, eventually becoming little more than a tumor-like mass containing a rapidly pulsing pair of testicles, sharing the female’s circulatory system and nourishment. The massive female, lacking secondary sexual traits, begins producing eggs only after fusing with a male. The truly grim part is that this doesn’t guarantee lifelong monogamy, as some species may have as many as seven other lifelong parasitic suitors fused with the female’s flesh alongside the original male.
5. Parasitic Degeneration
Nature has a penchant for efficiency and specialization. A common misconception about natural selection is that evolution inherently leads to increased complexity over time. Parasites provide a stark counterexample to this idea. These organisms have minimized their bodies to the simplest possible form in order to remain undetected while feeding off the fluids and tissues of their hosts. Disturbingly, parasitic species make up at least 40 percent of all life on Earth.
A recent discovery revisited the obscure Myxozoan group, recognizing them as a bizarre type of degenerate jellyfish. These creatures have been reduced to a mere few cells, with no distinct digestive system and an unusually tiny genome, 20–40 times smaller than typical. Myxozoa have shed some of the core traits common to all animals, such as Hox genes that control basic multicellular functions, challenging the very definition of the animal kingdom and blurring its boundaries.
A particularly striking example of parasitic degeneration is found in the female barnacle Rhizocephala. As a larva, it attaches to a crab’s body and starts its transformation. As it matures, it changes from a cyprid into a fungus-like mass of hyphae, completely devoid of any bodily segmentation or organs. This mass infiltrates the host's body, draining nutrients and manipulating its behavior to ensure reproductive success. Adult Rhizocephala have no brains and only rudimentary nervous systems, making them appear far more monstrous than H.R. Giger’s most grotesque creations.
4. Colonial Development
After exploring how minimalist animals can become, let's dive into the unsettling ways that natural selection has found to reconstruct these pieces into something more complex.
Picture a body not made of individual cells, but of thousands of tiny, genetically identical copies of yourself, each one fused together with its own skin... and all moving in perfect harmony to carry out essential bodily functions. Your more rigid structures would likely be the calcified, compressed remains of hundreds of sacrificed mini-you's. Delightful, right? Although underexplored, such bonded superorganisms are not uncommon in nature, especially among Cnidarians (jellyfish, corals, and anemones).
One of the most well-known and intricate examples is the Portuguese man-of-war (Physalia physalis), which, despite its jellyfish-like appearance, is actually a colony of interconnected clonal, jellyfish-like creatures called zooids, all working together as a single, enormous jellyfish superorganism. Other siphonophores related to it create long, gelatinous strands, some longer than a blue whale, yet remain barely studied due to their fragile nature, remote marine habitat, and solitary lifestyle.
Siphonophore expert Casey Dunn compares these creatures to massive collections of Siamese twins in various stages of degeneration, often consisting only of legs, mouths, or reproductive organs. Think of them as nature’s response to The Human Centipede. Dunn sees the siphonophore as raising profound questions about the concept of individuality in nature and is especially intrigued by the idea of siphonophore 'cancer,' where the spread of degenerate 'normal' creatures within a fused colony could foster selfish independence at the expense of the entire community.
However, this is merely the beginning of the story . . .
3. Infectious Prions
Even more basic than viruses, infectious prions are malformed, free-floating proteins that replicate by forcing other proteins to adopt their shape, progressively accumulating in the host's brain. Their remarkable simplicity makes them the ideal parasite, capable of spreading across species with ease, and their infections remain untreatable with current medical technology.
Proteins serve as the fundamental building blocks of all known biological life, yet they aren't alive by themselves. Despite this, these rogue proteins are still evolving. Research from the Scripps Research Institute showed that infectious prion cultures, when exposed to chemical inhibitors, adapted to produce resistant strains in much the same way bacteria or viruses evolve. Even without genetic material, in this case, natural selection operates at a level beneath genes and chromosomes, within the realm of complex organic molecules.
Infectious prions don't qualify as living organisms, even in the broadest sense, yet they remain adaptive products of natural selection, capable of wreaking havoc on their animal hosts, as seen in diseases like mad cow and kuru. New studies even link prions to Alzheimer’s and Parkinson’s, suggesting that, under specific conditions, they could be infectious.
It’s not so much that nature or the molecular makeup of life has it out for us. It’s more that it simply has no regard for us at all.
2. Jumping Genes
To truly begin understanding natural selection, it's useful to expand our view of what constitutes an ecosystem and its constituent elements. Just as survival of the fittest operates at the environmental level for animals, a comparable process unfolds even at the cellular scale. Richard Dawkins's concept of 'The Selfish Gene' finds a perfect illustration in parasitic genetic sequences known as transposons, which are thought to have emerged from viral invasions into the DNA of our ancient, reptilian ancestors.
Transposons are believed to make up approximately one-half to two-thirds of the human genome. They are short, self-replicating DNA sequences that appear to serve no immediate purpose. A small fraction of them seem to have been re-integrated into the genome, fulfilling specific roles in bodily functions. However, their primary function seems to be creating 'raw noise and variation' in the genome, offering a foundation for beneficial mutations and the process of evolution.
According to the nearly neutral theory of molecular evolution, transposons thrive by existing as silent mutations, meaning they don't directly influence the organism’s physical form. If a transposon alters the function of nearby genes, it risks harming the host’s fitness and could eventually be eliminated from the gene pool. This insight challenges the notion of stable, separate bodily identities, revealing it as another human-centered illusion. At every level of selection, a constant battle occurs, even down to the most basic molecular structures. Parasites are pervasive at all levels within us, and in many ways, we are merely iterations of their influence.
1. Parasitic Cancers
The Tasmanian devil (Sarcophilus harrisii) has seen its population plummet by 80 percent since 1996 due to the spread of infectious facial tumors. Devil facial tumor disease (DFTD) originated from a single animal and rapidly spread as the devils engaged in their naturally aggressive fights and bites. These tumors grow quickly, reaching large sizes in as little as six months, eventually killing the host by obstructing its feeding, spreading to other organs, or causing blindness.
A similar form of sexually transmitted cancer, discovered in dogs, known as canine transmissible venereal tumor (CTVT), sustains its growth by hijacking the mitochondria of its host cells. This process has been ongoing for thousands of years.
Parasitic cancers provoke deeply unsettling questions about what defines a living organism. These cancers, having undergone genetic mutations, being self-replicating, and acting in ways that deviate sharply from the host species' normal cellular behavior, could be more accurately described as—brace yourself—highly degenerate clonal parasitic mammals. While viruses hover on the edge of life, these cancers seem to have squirmed their way into the realm of living beings as well. Indeed, cancer itself has become a living animal in its own right.
