Why Crabs Walk Sideways

Evolutionary scientists admit to
finding “no intermediates” in crab
locomotion. It originated once.

Sideways Surprise
Evolutionists Admit Crabs’ Sideways Locomotion Originated Once

by Dr. Sarah Buckland-Reynolds

The sideways walk of crabs is one of nature’s most iconic spectacles. For those of us who have close access to water-based ecosystems, their walk is so familiar that we may rarely pause to ask why it exists or how it came to be.

Notwithstanding, a recent preprint of a research paper tried to find a Darwinian explanation for it.

Evolution of sideways locomotion in crabs (Taniguchi et al., 2026, eLife, 21 April 2026). This paper tried to analyze the origin of crabs’ iconic sideways walk. The authors concluded that the

“…ever-biggest behavioral dataset on crab locomotion reveals that sideways locomotion originated only once from the forward locomotion ancestor, rather than through multiple independent origins” (Taniguchi et al., 2026; italics added).

Bright red crabs make annual migrations on Christmas Island south of Sumatra. During the migration season, tied to the moon and tides, more than 50 million of them walk for 5 to 7 days for up to five miles nonstop to the sea to spawn. The hatchlings, mere millimeters in size, float in the sea as plankton till able to walk, then march to join their parents in the interior of the island (Photo from Wikipedia). Watch the migration on CBS News.

Despite their reliance on evolutionary frameworks, they also admit that there were “no intermediates” between species of crabs with forward locomotion to those that walk sideways.

In this article, we examine the implications of this admission of ‘singularity’ of appearances to traditional Darwinian evolutionary gradualistic theory, and how the sudden appearance, uniqueness and stability of crab locomotion suggest foresight and design rather than the result of mutations and natural selection.

Crabs’ Sideways Walk: A Rare Innovation

While crabs’ sideways walk can appear comical, it confers several advantages to crabs. Among these include rapid bidirectional speed, unpredictable escape routes, and flexibility in diverse habitats.

According to evolutionary researchers, Taniguchi et al., crabs’ sideways walk is believed to have been traced back to the earliest Jurassic period, around 200 million years ago (earliest Jurassic, immediately post–Triassic–Jurassic extinction). According to evolutionary geology, this was during a recovery interval marked by Pangaea rifting, expansion of shallow‑marine habitats, and the Mesozoic Marine Revolution, which opened new ecological opportunities.

In this context, the researchers acknowledged that crabs rapidly diversified. Coinciding with this diversification, sideways locomotion was said to have “appeared” and became fixed at the base of Eubrachyura.

This singular origin poses several issues with conventional evolutionary expectations. Among these include:

1. Lack of gradual intermediates: In the eLife press release, the conclusion was described as follows:

“Their analyses revealed that the change to sideways walking occurred only once from a single, forward‑walking ancestor at the base of Eubrachyura… and then remained highly conserved across true crabs”

As was further stated by the researchers:

“…forward and sideways locomotion are alternative modes; one cannot adopt both simultaneously”

These statements underscore the binary, threshold nature of crab locomotion. In evolutionary terms, gradual transitions are expected, with small steps accumulating into new traits. But in crabs, locomotion is not a spectrum; it is either forward or sideways, with no intermediates observed.

This means that, unlike conventional Darwinian theory, crabs’ sideways walking could not have emerged through incremental mutations that slowly shifted orientation. Instead, it required a complete reconfiguration of anatomy, neurology, and behaviour all at once: joint flexibility in the lateral direction, thorax elongation, and reduction of motor neurons controlling proximal leg muscles. Such interdependent changes point to integrated design rather than piecemeal evolution. The significance is that sideways locomotion challenges conventional evolutionary expectations by showing a trait that appears suddenly, functions as a complete system, and resists gradualist explanation.

2. Rarity versus convergence: Another challenge to evolutionary expectations is the contrast between the theorized multiple phases of evolution of distinct morphological traits like carcinisation (crab-like body forms) across decapods, but the single evolutionary appearance of sideways locomotion. The researchers themselves highlight their astonishment:

“This single event contrasts starkly with carcinisation, which has occurred repeatedly across decapod species. This highlights that while body shapes may converge multiple times, behavioural changes such as sideways walking can be rare”

Editor Note: This is another illustration of the flexibility of the Stuff Happens Law (natural selection) to explain anything, even opposites.

This rarity contradicts expectations of repeated convergence under natural selection. The scientists themselves acknowledge the rarity of the phenomenon as a general observation of species stating that:

“Despite this advantage, sideways locomotion has clearly been difficult to evolve across the animal kingdom”

Evolutionary theory fails to account for why this sudden trait appears to be so perfectly integrated into the behaviour of crabs. Evolutionary theory cannot answer this without resorting to speculation.

3. Integrated complexity: A third challenge posed is the complexity required for crabs’ sideways motion. Sideways locomotion requires coordinated anatomical, neurological, and behavioural changes, including but not limited to joint flexibility, thorax elongation, and motor neuron reduction. Such interdependent systems cannot evolve piecemeal without collapsing functionality. Moreover, this mode of locomotion, while difficult to explain by evolution, offers advantages to crabs, as noted in the press release:

“The single origin and diversity of Eubrachyura are consistent with the idea that sideways walking acted as a key innovation that contributed to the ecological success of true crabs. One likely adaptive advantage of this mode of travel is the ability to move rapidly at similar speeds in both lateral directions to allow for easier escape from predators. Despite this advantage, it has been difficult to evolve across the animal kingdom, possibly because it affects other behaviours such as burrowing, mating and foraging. The authors say it therefore represents a unique event that has occurred only in true crabs, and potentially crab spiders and leafhopper nymphs.”

According to Darwinists, multiple groups of crustaceans (phylum Arthropoda) have undergone carcinization by convergent evolution. Cartoon by Brett Miller. Used by permission.

Superior Engineering in Motion

A closer look at the engineering involved in crabs’ sideways motion further uncovers its engineering brilliance.

Unlike forward locomotion, which aligns with the body’s longitudinal axis, sideways walking requires a complete reorientation of the crab’s anatomy and neurology. The thorax is elongated laterally; joints are re‑engineered for flexibility in the sideways plane, and motor neurons controlling proximal leg muscles are reduced to streamline movement. These changes are not isolated tweaks but interdependent modifications that must work together seamlessly. As the study notes,

“modern sideways-moving crabs likely share the same anatomical, neurological, and developmental mechanisms, such as the reduction of motor neurons that control muscles of proximal legs” (Taniguchi et al., 2026).

This integration reveals a system that could not have been assembled through piecemeal processes. The sideways walk provides crabs with rapid bidirectional speed, unpredictable escape routes, and the ability to exploit diverse habitats. Each component functions like parts of a machine, engineered for precision and efficiency.

Evolutionary Side-stepping?

Despite the obvious markers of design, the authors persisted in framing their explanations within a Darwinian lens. While evolutionary gradualism struggles to account for such a leap, the contentions are often downplayed by framing traits as “key innovations” (17 instances in the article), and with the circular reasoning acknowledging its benefits as keys to its survival – while not addressing the unexplained origins of the phenomenon.

In the words of the press release, for example, it is said that: “Sideways locomotion may have contributed significantly to the ecological success of true crabs” (Kawabata, 2026). However, the very uniqueness of this locomotion, its sudden appearance, its stability across thousands of species, and its occasional reversions, suggests foresight and design in its origins, rather than evidence of it being an evolutionary trait.

Broader Implications: Modes of Locomotion and Design

The authors conclude: “Modes of locomotion—such as walking, swimming, and flying—fundamentally shape how animals interact with the environment” (Taniguchi et al., 2026). Indeed, locomotion is foundational. But the rarity of sideways locomotion, stability, and its integrated complexity point to design. Sideways locomotion being a threshold phenomenon, requires precise conditions, and complete systems to function. Despite Taniguchi and colleagues continually framing these observations in evolutionary terms, their conclusions have revealed yet another powerful example of design.

The crabs’ sideways walk reminds us that remarkable engineering exists in even the ‘lowliest’ creatures. All creatures proclaim their own unique testimony to the Presence of a Divine Designer: a fact that no genuine truth-seeker can legitimately side-step.

Dr. Sarah Buckland-Reynolds is a Christian, Jamaican, Environmental Science researcher, and journal associate editor. She holds the degree of Doctor of Philosophy in Geography from the University of the West Indies (UWI), Mona with high commendation, and a postgraduate specialization in Geomatics at the Universidad del Valle, Cali, Colombia. The quality of her research activity in Environmental Science has been recognized by various awards including the 2024 Editor’s Award from the American Meteorological Society for her reviewing service in the Weather, Climate and Society Journal, the 2023 L’Oreal/UNESCO Women in Science Caribbean Award, the 2023 ICETEX International Experts Exchange Award for study in Colombia. and with her PhD research in drought management also being shortlisted in the top 10 globally for the 2023 Allianz Climate Risk Award by Munich Re Insurance, Germany. Motivated by her faith in God and zeal to positively influence society, Dr. Buckland-Reynolds is also the founder and Principal Director of Chosen to G.L.O.W. Ministries, a Jamaican charitable organization which seeks to amplify the Christian voice in the public sphere and equip more youths to know how to defend their faith.  

Editor’s Bonus: Here is an AI answer to the question, “What are the main advantages of sideways walking in crabs?”

(Important note: the existence of an advantage does not support the notion that it originated by random mutation and natural selection. Remember also that AI answers are not authoritative and can echo mistakes stated on the internet. Use these answers only in a heuristic way to seek further information.)

• • If a crab tried to run forward quickly, its closely crowded legs would repeatedly clip and collide with each other, causing it to trip.
  • By moving laterally, the legs on the leading side pull the body forward, while the legs on the trailing side push it along. This synchronized, step-and-glide mechanical movement prevents the legs from crossing, allowing species like ghost crabs to reach top sprint speeds of up to 10 miles per hour.

• • A forward-walking animal must pivot its entire body weight to change directions, costing precious fractions of a second during an attack.
  • A crab can zig-zag erratically from side to side in an instant, making its trajectory completely unpredictable to a lunging predator.

• • Because a crab’s body is wider than it is long, walking sideways allows it to slip seamlessly into narrow, vertical tunnels without having to squeeze or bend awkwardly.
  • This lateral movement also ensures that its powerful front claws (chelipeds) remain pointed outward toward the entrance of the burrow, creating an instant defensive shield against any intruder trying to follow it inside.

• The mechanical joints of a crab’s legs function much like human knees, bending heavily outward and downward.
• This structural design makes it incredibly easy for them to push off vertical surfaces, step over high obstacles, and shimmy through tight rocky crevices without getting their main shell wedged or stuck.