Hodgkin's Law of Parallel Planetary Development was a biological theory first postulated by A.E. Hodgkin. The theory was that similar planets with similar environments and similar populations tended to gravitate toward similar biological developments over time. Although initially applicable only to biology, it was later expanded to include a tendency to move toward similar sociological developments as well with sentient beings. (ENT: "Strange New World"; TOS: "Bread and Circuses")

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The theory

Just as the finches of the Galápagos Islands provided the crucial biological clues that Charles Darwin used to develop the theory of evolution, the termites of the planet Loracus Prime were the inspiration behind Hodgkin's law of parallel planetary development. The theory was the brainchild of biologist A.E. Hodgkin, who first visited Loracus Prime as part of a science survey mission. As Hodgkin noted in his log, the native termite life of Loracus was remarkably similar to that of Earth, Vulcan, and several other Class M worlds. At first, Hodgkin considered the possibility that termites were brought to Loracus by early space travelers, or even that they were a meteorite-borne species, but he quickly realized that Loracus Prime's location in the middle of the Gagarin Radiation Belt ruled out either possibility. In fact, travel to the Loracus system had been all but impossible until the then-recent era of relatively clear stability of Loracus's star.

After careful testing of the termites' DNA, Hodgkin determined that the genus was clearly native to Loracus. This set up the question: why there was such an amazing similarity to terrestrial termites? Over the next decade and a half, Hodgkin slowly puzzled out the theory that would rock the biological world as profoundly as Darwin's had centuries earlier. (ENT: "Strange New World")

The next development in the theory was the realization that there was a tendency toward sociological as well as biological similarities where environmental conditions were similar. For instance, by the 2260s, Starfleet and other exploratory organizations had discovered numerous planets with humanoid populations that shared certain social constructs. Family units, spoken languages, furniture, space travel, dispute resolution through an organized legal process, organized war waged by governments – all of these were aspects of society that appeared to transcend any one single planet's societal development. (TOS: "Miri", "Bread and Circuses", "Patterns of Force", "The Omega Glory")

The Hodgkin theory was adapted to explain the observed instances of similarities in societies that had never had previous contact with each other developing along similar lines. The theory did not require identical development of a society, it simply offered an explanation for similarities. Finding nearly identical development was "virtually impossible" (as Spock remarked about the planet Ekos), and when found to be close to identical was viewed as an "amazing" example of Hodgkin's Law (as Captain Kirk remarked about the society on the planet 892-IV). (TOS: "Bread and Circuses")

Biological examples

Beginning with the lowly termites on Loracus Prime, there have been numerous examples of parallel biological development observed over time. Animals as diverse as the dog and the targ, the Capellan power-cat and the sehlat all independently developed fur, mouths, four legs, heads, tails, eyes, and other similar attributes, despite none of them being native to the same planet. (citation needed • edit)

Most striking is the apparent biological preference for the humanoid form for sentient lifeforms, observed across species as diverse as Vulcans, Klingons, Denobulans, Humans, and Ocampa. Part of this is doubtless due to the actions of an ancient humanoid species, one of the oldest known sentient species, and possibly the first humanoid race in the Milky Way Galaxy. According to a message the humanoids left behind, encoded in the DNA of various humanoid species and discovered in 2369, they had seeded many worlds, including Earth, with DNA "seed codes" that encouraged the development of similar humanoid life. (TNG: "The Chase")

Sociological examples

Many worlds have independently developed in ways that support the application of Hodgkin's law to societies. Several worlds in particular visited by the USS Enterprise in the 2260s showed exceptional examples of societies that developed in ways that were extreme examples of Hodgkin's Law.

Omega IV

Prior to the 23rd century, Omega IV had developed two cultures similar to those found on Earth: Americans and Asian Communists. The state of the cultures reached levels similar to those of Earth's 20th or 21st century before devastating bacteriological wars brought about a collapse of both civilizations. While independently developing an economic system based on capitalism and profit is not itself remarkable (e.g., the Ferengi), what set this planet apart for purposes of the Hodgkin theory was the extraordinary similarity of names, symbols, and even documents to those found on Earth. The name of one culture – the Yang – was clearly a derivation of "Yankee", while the name of the other culture – the Kohm – was equally clearly a derivation of "Communist". The Yangs had, prior to the wars, developed a flag and even a preamble to a Constitution that were virtually identical to those of the United States of America in the early 21st century on Earth. (TOS: "The Omega Glory")

Forgotten History explained this as actually the result of cultural contamination by the E.C.S. Philadelphia who had visited Omega IV sometime in the late 2140s. Noting the similarities between Yang beliefs and those of American democratic values they left replicas of American paraphernalia. E.C.S. Philadelphia

892-IV

The planet 892-IV had a land-mass/ocean ratio similar to Earth, although it possessed a significantly different topography. But in an "amazing" example of Hodgkin's law, it saw the development of a society that was remarkably like that of Earth's Roman Empire, although they used "colloquial 20th-century English" instead of Latin. It also independently developed its own Jesus Christ and associated religion based on his being the son of God. A major difference, however, was that unlike Earth, the Empire had not fallen by the time of the Enterprise visit in 2268. At that time, the Roman Empire dominated the planet, but at a 20th century level of technology. (TOS: "Bread and Circuses")

Captain R.M. Merik asserted that 892-IV had not experienced war since their equivalent of the 16th century, implying the period this Roman Empire established domination of 892-IV. However, it is pointed out "If this (Hodgkin's Law) is such a well-established law, why are Kirk and Spock surprised to find a Nazi civilization in Patterns of Force?" (The Nitpicker's Guide for Classic Trekkers, p. 217)

Earth Two

Unique in the annals of parallel planet development, in 2267 the USS Enterprise discovered the Earth Two. It was a world physically identical to Earth: it had the same mass, circumference, density, atmosphere, flora, and fauna. Even the topography was identical. The inhabitants of this world were virtually indistinguishable from Humans as well, although a biological accident had killed every single adult and left the remaining prepubescent children with extraordinarily long lifespans. The planet's inhabitants had reached at least a level of technology and architecture typical of the United States circa 1960 prior to the disaster. (TOS: "Miri")

Cloud cover on Earth Two appeared to be much less dense than on Earth, but that was most likely a means of showing similarity to an audience than an actual portrayal of the planet as envisioned. A canon explanation as to whether this planet and Earth simply developed naturally, or whether external forces were at work, was never provided. The William Shatner novel Preserver featured a return to this planet, wherein it was revealed the planet had been duplicated from Earth on a subatomic level by the Preservers. However, Forgotten History states that various subspace anomalies indicated the planet was from an alternate timeline.

Other possible explanations

Hodgkin was originally concerned that the similarities he saw regarding the termites on Loracus Prime were the result of contamination. While he ultimately dismissed that as a possibility, later discoveries have shown that there was far more biological and cultural contamination in the distant past than was known during his time.

Some major events that might provide either alternative or supplementary explanations for developments thought to be examples of Hodgkin's law include numerous visitors to Earth and other planets in the distant past (including Apollo, the Megans, and Kukulkan), as well as:

4.5 billion years ago An ancient humanoid species, one of the oldest known sentient species, and possibly the first humanoid race, seeded the oceans of many Milky Way Galaxy worlds, including Earth's, with "DNA codes" that encouraged the development of similar humanoid life. A message the humanoids left behind describing this was discovered in 2369. ( TNG : " The Chase ")

Although much was made in the episode of a possible Voth civilization on Earth, the episode never concluded that it definitely existed. It is equally plausible that the Preservers relocated the young species as either Voth or Eryops to the Delta Quadrant. And if the Voth arose on Earth and migrated out from there, they may have contaminated a number of planets with terrestrial DNA.

600,000 years ago The Arretans colonize many worlds across the galaxy, possibly including Vulcan as well as potentially a number of other planets bearing Human-like or Vulcan-like life in the present day. ( TOS : " Return to Tomorrow ")

45,000 years ago Extraterrestrial visitors, known as the "Sky Spirits", visited Earth and genetically altered a group of people who would later be known as the Native Americans. ( VOY : " Tattoo ")

They may have introduced contaminating genetic similarities on other planets.

38th century BC In an attempt to prevent mankind from destroying itself in the distant future, an alien species took Humans to be raised on a planet located 1,000 light years from Earth. A descendant of these Humans, Gary Seven was discovered by the crew of the Enterprise manipulating events on Earth in 1969. ( TOS : " Assignment: Earth ")

The extent of their travels in time, and the influences they may have had on other planets' biological development are not known.

Background information

"Hodgkin's Law" was a writer's device used to reconcile Star Trek: The Original Series science-fiction themes with obvious budget limitations. Gene Roddenberry wrote in his original pitch:

The "Parallel Worlds" concept makes production practical by permitting action-adventure science fiction at a practical budget figure via the use of available "Earth" casting, sets, locations costuming and so on.

As important (and perhaps even more so in many ways) the "Parallel Worlds" concept tends to keep even the most imaginative stories within the general audience's frame of reference through such recognizable and identifiable casting, sets and costuming."

Even within the Original Series an alternative to "Hodgkin's Law" in the form of the Preservers from "The Paradise Syndrome" was presented as an explanation for "why there were so many humanoids scattered through the galaxy." In Star Trek: The Next Generation, the ancient humanoids from "The Chase" were yet another alternative to "Hodgkin's Law". Both these races not only provided a source for possibly all of the galaxy's remarkably Human-shaped life, but the ability for alien species to cross-breed as well.

The explanation for the similarities between Humans and many alien species bears a number of similarities to non-canonical explanations of the mirror universe. In several novels and comic books, writers have attempted to define a point at which the mirror universe and our universe diverged, given the overwhelming similarities in physical appearance of people and places.