Embryo space colonization
Embryo space colonization is a theoretical interstellar space colonization concept that involves sending a robotic mission to a habitable terrestrial planet transporting frozen early-stage human embryos or the technological or biological means to create human embryos.  The proposal circumvents the most severe technological problems of other mainstream interstellar colonization concepts. In contrast to the sleeper ship proposal, it does not require the more technically challenging 'freezing' of fully developed humans (see cryonics).
- The most straightforward concept is to make use of frozen embryos. Modern medicine has made it possible to store frozen embryos in various low-development stages (up to several weeks into the development of the embryo).
- The technologically more challenging but more flexible scenario calls for just carrying the biological means to create embryos, that is various samples of donated sperm and egg cells.
- Going a step further, the spacecraft "cargo" could be limited just to the genetic information of humans stored in as computer files. In this case, sperm and egg cells would need to be recreated by a biosequencer at the target planet (this proposal is currently not technologically feasible).
Mission at target planet
Regardless of the "cargo" used in any embryo space colonization scenario, the basic concept is that upon arrival of the embryo-carrying spacecraft (EIS) at the target planet, fully autonomous robots would build the first settlement on the planet and start growing crops. More ambitiously, the planet may be terraformed first.  Thereafter the first embryos could be unfrozen (or created using biosequenced or natural sperm and egg cells as outlined above).
In any event, one of the technologies needed for the proposal are artificial uteri.  The embryos would need to develop in such artificial uteri until a large enough population existed to procreate by natural biological means.
Comparison to other interstellar colonization concepts
- Proposals of sleeper ships and generation ships require very large spacecraft to transport humans, life support systems and other equipment or food as well as an even larger propulsion system for a long period in time. Even optimistic proposals would require such a major effort for such ships that the resources required on Earth would involve a large part of mankind devoted to the mission or would even exceed available resources. In contrast, an EIS would have feasible small dimensions in the range of today's spacecraft, as the most important "cargo" would not need much space or weigh very much.
- Sleeper ship proposals call for freezing adult humans. While there is research into hibernation, the complexity of a living fully developed human body may make the sleeper ship proposals much more difficult.
- While sleeper ships and generation ships would deliver to a prospective colony world a population that has undergone some degree of education, training, and socialization in areas reconcilable with those of the sponsor culture (e.g. historical, scientific, and technical education, language acquisition, an understanding of the original mission and broader cultural norms), individuals who are born into colony worlds through embryo space colonization would initially lack this education. 
Difficulties in implementing the concept
Like every proposal for interstellar colonization, embryo space colonization depends on solutions to still-unsolved technological problems. Some of these are:
- Robotics: Whether it will be possible to develop fully autonomous robots that can build the first settlement on the target planet and raise the first humans, is unclear. Because the initial probe must be maximally compact, the industrial robots that build the habitat would themselves have to be built autonomously from local materials. Though such technology does not yet exist, there are strong economic incentives to develop it, which are unrelated to space colonization.
- Artificial Intelligence: It would be challenging to create an artificial intelligence that could serve as an adequate artificial parent and successfully raise human children who have no contact with other human beings. Its design would have to include strategies for the transmission of terrestrial culture and language, as well as the prerequisites for healthy psychological functioning, to persons who cannot interact with Earth.
- Artificial Uterus: Artificial wombs are not available today. Scientists are however already working on this technology.
- Long-duration computers: Computer hardware would need to function reliably over long periods of time, in the range of several thousands of years.
- Propulsion: Furthermore, a propulsion system would be required that could accelerate the EIS to a high speed and slow it down again upon nearing the destination. Even assuming a speed one hundred times faster than any of today's spaceprobes and a target planet within a couple of hundred light years would lead to a journey lasting several thousand years.
- Exoplanet found: Finally this depends on the existence of an exoplanet qualifying for colonization within a reachable distance. Current science missions like COROT, Kepler or Darwin may very well yield results for this requirement within the next 3 to 4 years.[when?]
Further unknowns that affect the feasibility of embryo space colonization are:
- Biological: Will genetic material survive intact on a space mission that could potentially last centuries? Exposure to cosmic rays is known to irreparably damage DNA. What other symbiotic lifeforms does a human need to live a healthy life? For example, gut flora and many other species of microorganisms may be necessary for proper biological and immunological functioning. Babies normally acquire these from their mothers and the wider environment, but this would not be the case for embryos in colonization ships.
- Ethical: In addition to the question of whether it is technically feasible to raise children without human contact, there is the further question of whether this is morally permissible. We ordinarily find it unethical to deliberately create children that will grow up without parents, yet embryo space colonization requires this. Controversial value judgments would also need to be made about whose DNA should be the basis of the space colony. Should it selected by some metric of merit, or randomly from the general population? Either choice presents ethical problems. Should the parenting AI firmly steer the children to maximize the chances of the colony's success, or should it accept the risk of allowing them significant autonomy? Which languages and cultural values should be transmitted to the colonists? Should we raise them according to some value system that exists on Earth, or create one that is somehow optimized? Are there truths that should be kept from them? The possibility of a new civilization that starts without a cultural legacy might appeal to cults that want their values to become a norm for an entire society. Is it permissible to allow them have their own embryo colonies, where the AI indoctrinates the colonists only in the cult's value system? The difficulty of answering these and other ethical questions may become a non-technological obstacle to embryo space colonization.
Examples in fiction
- James P. Hogan's novel Voyage from Yesteryear features a planet that was colonized a few generations ago by an automated ship capable of abiogenesis from computerized DNA records of humans and other Earth life, now being visited by a more advanced interstellar spacecraft capable of carrying an adult crew.
- Richard Morgan's novel, Broken Angels (a sequel to the first Takeshi Kovacs novel Altered Carbon), shows Embryo Colonisation as the only one humanity could have ever developed, with only STL travel and string communication being available to them. It describes also, its stages and flaws.
- Tomasz Kołodziejczak's novel Caught in the Lights (the second book in the Solar Dominium dilogy) describes embryo space colonisation in two stages, the robotic and the embryonic. There was a time period in the book's universe called "The Sperm Wars", in which embryos were forced to rapidly grow and fight to defend the colony. Most of those children never reached adulthood due to either forced growth suspension, or being killed in action.
- Jack Williamson's Manseed has as a protagonist one of the robots responsible for protecting and assisting colonists created on a new planet by an automated "seedship", though in this case the colonists are "born" as full adults and with implanted knowledge recorded from preexisting humans via mind transfer technology.
- In Yukinobu Hoshino's 2001 Nights manga, Night 4 showcases an interstellar mission where an automated ship bearing frozen embryos is launched with the help of a comet. Two later chapters, or "Nights," in the series explore what happens to the mission after it touches down on the surface of the destination world.
- In David Brin's The River of Time (1986), the short story Lungfish - which prominently features Von Neumann probes - mentions a class of probe called Seeders which seem to be a type of self-replicating EIS.
- In Alastair Reynolds' Revelation Space series a faction of humanity known as "Amerikano" sent numerous colonization ships out into the galaxy. Almost all of these missions ended in failure, although they did have some success. One noteworthy example (although only a partial success) is the planet "Yellowstone", a planet in the Revelation Space Trilogy and the primary location for another novel in the same setting, "Chasm City", as well as one of the major human clusters in the galaxy.
- In Arthur C. Clarke's novel, The Songs of Distant Earth (1986) humans respond to the prospect of unavoidable doom by launching a series of robot colony seedships into space, to continue Earth life after the destruction of the homeworld (caused by the Sun becoming a nova). Thalassa is colonised by one such ship, but loses contact due to a natural disaster. As technology advances the mantle of colonization is then taken up by sleeper ships. Meanwhile, just as the predicted time of cataclysm is due to elapse, vacuum energy technology is invented to allow the construction of one near-light-speed vessel, the Magellan, which is launched to build the last colony of mankind. (Previous colony ships involved frozen embryos, or various forms of DNA synthesis. In Magellan, a living crew is transported in cryonic suspension.) The Magellan will also assist in terraforming the colonists new planet, Sagan Two.
- In the episode Scorched Earth of the TV Science Fiction series Stargate SG-1, a ship created by extraterrestrials known as the Gadmeer was in the process of 'terraforming' a planet (or rather, adapting it for non-terran life). It contained genetic information from all the life forms of the sulphur-breathing Gadmeer's home planet, all the knowledge of the Gadmeer, and things of cultural importance to the Gadmeer, and was to re-create them once the 'terra'-forming process was completed.
- In the animated film Titan A.E., during the destruction of Earth by alien invaders, a ship is launched with the DNA of every species on the planet.
- In Vernor Vinge's 1972 short story "Long Shot", the story of an attempt at embryo space colonization is told from the point of view of the artificial intelligence bearing the embryo through interstellar space. In his Marooned in Realtime, which posits a society with few remaining Earthlings, artificial womb technology is discussed as necessary to rebuild the population of Earth, since a sufficient rate of natural reproduction would be unfeasible.
- In Pamela Sargent's novel Alien Child (1988) humanity is extinct except for two children raised by aliens that were found in a storeroom full of embryos. The storeroom was built before humanity destroyed itself with wars. The children have to decide whether to revive the other embryos or let the human race die completely.
- Embryo space colonization is treated with derision in Kurt Vonnegut's satiric short story The Big Space Fuck, collected in Palm Sunday (1981).
- In Andymon (1982), one of the most popular science fiction novels of East Germany, robots raise children from frozen embryos to colonize the eponymous planet.
- Crowl, Adam et al. "Embryo Space Colonisation to Overcome the Interstellar Time Distance Bottleneck". Journal of the British Interplnanetary Society, 65, 283-285, 2012.
- Lucas, Paul (2004-06-21). "Cruising the Infinite: Strategies for Human Interstellar Travel". Retrieved 2006-12-24.
- Brin, David (1987). "Lungfish". The River of Time. Davidbrin.com. Retrieved 2006-12-24.