Centauri Dreams is happy to welcome Dr. Cameron M. Smith, a prehistorian at Portland State University’s Department of Anthropology in Portland, OR, with an essay that is the capstone of this week’s worldship theme. Dr. Smith began his career excavating million-year-old stone tools in Africa and today combines his archaeological interests with a consideration of human evolution and space colonization. He is applying this interest in his collaboration with the scientists at Icarus Interstellar’s Project Hyperion, a reference study for an interstellar craft capable of voyaging to a distant star. Recently Dr. Smith presented a paper at the NASA/DARPA ‘100 Year Starship Study’ conference in Houston, Texas. His recent popular science publications in this field include “Starship Humanity” (Scientific American 2013) and the book Emigrating Beyond Earth: Human Adaptation and Space Colonization (Springer-Praxis, 2013). We can look forward to a follow-up article to this one in coming weeks.
by Cameron M. Smith
1. Interstellar Migration: An Insurance Policy for the genus Homo
Planets orbiting distant stars are now being discovered at a rapid pace, with hundreds known and countless worlds implied. As an anthropologist, I take a wide and long-term look at human evolution, and this development is very exciting to me; those almost unimaginably-distant planets are where humanity is headed, in the longer or shorter term. Humanity has been characterized by spreading itself wide across the Earth, and after first colonizing Mars we will surely wish to go farther, just as, in Polynesian legend, the siblings Ru and Hina—having explored the whole Pacific—chose to build a special vessel for a trip to the moon. Although civilization as practiced so far is perhaps its own worst enemy, I am optimistic that humanity’s better side will generally prevail, and that our species will invest in space colonization as an insurance policy for our lineage. Figure 1 indicates the five most recent mass-extinction events in Earth history, and Figure 2 indicates that even in recent times, civilizations have repeatedly collapsed and disintegrated, with no guarantee of recovery [click on figures to enlarge as needed]. In the larger picture, over long time, space migration is the best means of surviving such disasters.
Recently humanity has spent just over a generation exploring the solar system just beyond our atmosphere, sometimes with robotic voyagers, and sometimes with our own bodies; for the past 23 continuous years human beings have already lived off of the surface of the Earth in various orbital stations; cosmonaut Sergei Krikalev has spent over 800 days in space, and his colleague Valeri Polyakov once remained continuously in orbit for well over a year. Despite some close calls, nobody has died in this nearly quarter-century of continuous space habitation, which has taught us some basics of space biology. Clearly, our species’ technical capacities are superb, and the essential technologies for long-term stays in space are being sketched out. We also have realistic destinations in view, and highly-focused, forward-thinking physicists and mathematicians working on how to reach those destinations with unique propulsion systems.
Will developing space technology be enough, however, to pave a way to space colonization? It will be part of the equation, but the equation is not complete. Space colonization will be about humans living off of Earth, but human biology off of Earth is only barely understood, and only in the cases of the individual physiology of adults, for short periods of the entire life course. Space colonization, however, will be about humans living out entire lifetimes—from fertilization to embryo development and so on through adulthood—and in populations (rather than just individuals) and populations over multiple generations, not short stints in Earth orbit. For these reasons, at least, we need an anthropology of human space colonization. Anthropology studies the biocultural evolution of our lineage and some of our closest relatives. In this article I would like to introduce some of the biological issues involved in space migration, specifically among multigenerational, interstellar voyages. In a second article I will introduce cultural evolution in such vessels.
2. Where to Begin?
Space colonization will be a continuation of human evolution. I don’t mean this in the shallow sense of a ‘March of Progress’, but in a deeper, more mature and more useful way. Humans are life forms, and thus we change through time, both biologically and culturally. When such change allows us to live in new places—for example, the Canadian Arctic (over 5,000 years ago), the islands of the Pacific (over 3,000 years ago), or Earth orbit—it is called adaptation. Space colonization, then, will be an attempt at adaptation, and if we want to succeed in this adaptive endeavor we should be informed with everything we know about evolution in general and adaptation in particular.
Generally speaking, while it is clear that humanity has adapted to many ecological niches over time, it is equally clear that our adaptation differs significantly from that of most other life forms. This is because humanity adapts more culturally and technologically than biologically; witness our essential biological similarity across the globe, despite a few regional variations in skin color, hair texture and so on. Rather than adapting largely by body, then, we adapt largely by mind, which generates complex behavior (such as adjusting our kinship rules and sex taboos to match our distribution across landscapes) and complex technologies (including everything from inventing sailing vessels and stellar navigation in the Pacific to walrus-hunting watercraft and harpoons in the Arctic) allowing our species to flourish in places never dreamed of by our earliest bipedal ancestors. Having said this, humanity continues to evolve biologically even today, and will continue beyond Earth, and that evolution must be considered.
While technology is a cultural invention, in this article I will leave the technologies of space colonization to the engineers, and focus on the biological issues involved in interstellar voyages. These have been sketched out before in disparate literature; here I would like to update the material and consider it specifically in the case of current draft studies of interstellar vessels.
3. A Thoughtscape for Planning Interstellar Voyages
Current plans for interstellar voyaging essentially envision a gargantuan starship hurtling on a one-way voyage from Earth towards a distant star system. Interstellar craft would have to be very large—perhaps kilometers on a side—to house populations in the thousands, as I will discuss below. The most distinctive characteristic of these colony ships is that they would essentially be closed systems, with no opportunity for bringing in new genes, maintenance or repair materials, or consumables, such as water or breathing gases. These ‘Space Arks’ would have to be regenerable and self-contained, a fascinating challenge not just in engineering but also concerning biology and culture.
Presuming that we could build such vessels, the main engineering challenge is going to be propulsion (an issue being tackled right now by the scientists at Icarus Interstellar). Our galaxy, the milky way, contains an average density of .004 stars per cubic light year, and the closest star to Earth, Proxima Centauri, is 4.2 light years away. At light speed that is 4.2 years of travel time, but today, attaining that speed (or, technically, something very close to it, as light speed is not thought to actually be attainable by anything other than individual photons or similar particles) is unrealistic. How fast can we go? The fastest humans have moved is about 24,790mph (just over .00003% the speed of light), on Apollo X in 1969. At that pace, Proxima Centauri is about 140,000 years away. Maybe we can do much better, though. In the last 150 years we have increased human travel speeds almost a thousandfold up from the locomotive’s 30mph (the Voyager spacecraft speed along at about 1,000 times the speed of a locomotive). If we can do something similar in the near future, travel times become significantly more manageable. A 100-fold increase in speed from Apollo X (bringing us to just under 3,000,000 miles per hour) would take us to Proxima Centauri in something under 1,400 years. This is getting manageable, but is still a long time; imagine launching the ship during the Dark Ages (just after the collapse of Rome, about 1,400 years ago) and having it arrive at its destination in the time of such oddities as desktop computers. If, however, we manage to make a 1,000-fold increase in speed (bringing us to about 30,000,000mph) in the next century or so, then the heavenly wonders of Proxima Centauri (actually we don’t know what it is like there, yet, but I am being optimistic) could be achieved in about 140 years (see Figure 3). This is a very manageable timescale, a distance only that from today’s world to that of 1872–less than five generations distant and essentially comprehensible.
This, then, is the thoughtscape I am exploring in this article; voyages on the order of under two centuries, carrying some thousands of people (a number discussed below) before reaching another solar system. What biological and cultural issues need to be addressed on such voyages? While the answer will be some time coming (I’m currently investigating it in research for my forthcoming textbook on the anthropology of space colonization), I can sketch out some below.
4. The Biology of Interstellar Voyaging
While evolutionary biology is currently undergoing significant revision in the light of new genomic data, the principles of evolution are largely intact. These include the four main processes (genetic mutation, selection, migration and drift) that change the properties of the gene pool over time. Each is discussed below.
4.1 The Biology of Interstellar Voyaging: Mutation
Mutation is ultimate source of new variations, such as coarser hair, or darker skin than one’s fellows. In common speech a mutation is thought of as being deleterious, but scientifically speaking mutations could be advantageous, disadvantageous or neutral. Some mutation is a result of radiation, and interstellar voyage designs will have to consider trapped particles, radiation energy near Earth and constrained within the Van Allen belt (and presumably about other planets with analogs of the Van Allen belt; cosmic rays derived from many sources outside this region, and solar radiation blasts out of suns. Radiation can degrade biological tissues and cell functions, and it can also be a powerful mutagen, altering DNA; recently it has been suggested that cosmic radiation could increase the incidence of brain disorders.
Certainly radiation is an issue to be addressed, but it does not seem to be a showstopper for human space colonization. First, many shielding schemes have been devised. In interstellar craft some kind of radiation shielding will be necessary, but because shielding is heavy, designers will probably try to get away with as little as possible. How thin is too thin? This is difficult to answer; aside from clear cases of lethal exposure to high doses of radiation, its long-term effects are mysterious. One 1995 study tracked the health of over 70,000 children of parents who were within a kilometer of the nuclear bombings at Hiroshima and Nagasaki, Japan, during World War II. Surprisingly, there was no statistically significant difference between the study population and populations of children of non-irradiated parents, in terms of malignant tumors in early age, differences in sex of offspring, chromosomal abnormalities and other mutations. On the other hand, recent studies have shown highly elevated mutation rates in people living near the Chernobyl disaster site. We have plenty to learn.
The second reason that radiation will not be a deal-breaker for interstellar voyaging is that mutagenesis itself has recently been found not to be largely the result of such ‘one-off’ ‘zaps’ from space, but rather more the result of the failure of DNA-repair mechanisms on the molecular level itself (over 300 such mechanisms and processes have been identified in the human genome alone). Thus, DNA repair therapy will probably be a large part of mitigating radiation issues in interstellar voyages.
In short, anywhere beyond Earth’s natural radiation shielding, under which we have evolved for millions of years, the mutagenic environment will be new and therefore a candidate for affecting our genome. Obviously we will use technology to mitigate such effects, including shielding and management of DNA repair, but we must remember that we do not know everything and that it will take time to adjust—both biologically and culturally–to new environments.
4.2 The Biology of Interstellar Voyaging: Selection
Natural selection occurs when life forms are prevented from reproducing—or simply have less offspring than others of their generation—due to their genetic characteristics. For example, a fly born without wings is unlikely to have offspring, or at least less offspring than its cohort (because of its reduced health and reduced ability to find mates) such that ‘wingless’ genes are likely to be ‘selected out’. Concomitant to most ‘selection against’ certain characteristics is selection ‘for’ alternatives. It’s often thought that humanity has halted natural selection with modern medicine and technology, but this is an illusion; many people continue to die before giving birth because of their genetic properties, particularly in populations without access to modern health care; and several recent studies have shown natural selection to be underway in modern populations. Even so, by the time of interstellar travel health technology will be much advanced…and yet selection will continue, for at least three reasons.
First, conditions off of Earth will differ from the conditions on Earth, where a relatively narrow environmental envelope of temperatures, atmospheric pressures and elemental compositions, nutrient supply and gravity have prevailed. The conditions in interstellar craft might well approximate these conditions, but much experimental data indicates that even small alterations in such variables as breathing gas composition and pressure can negatively effect gene expression (the switching on and off of genes on very complex schedules) and development of vertebrate embryos during the critical phases of early formation (e.g. gastrulation). We will of course try to control such variables, but it is unlikely that we will be able to anticipate everything. It seems certain that there will be a degree of increased infant mortality as the human genome adjusts to new conditions in interstellar colony craft, however carefully we design them. I am currently researching the genetic aspects of human development and the life course in environments slightly different from those on Earth.
Second, selection will likely play out in the cases of sweeps of novel diseases through interstellar craft populations. Again, we will be very careful, but it is impossible to anticipate all biological change, and in smallish populations (e.g. the 10,000+ that I suggest for interstellar craft; see below) inhabiting closed environments, sweeps of new disease, I believe, might well occur. Whether such sweeps structure the interstellar craft genome structurally is impossible to know, but we must be prepared for this possibility.
Finally, most interstellar voyage plans head not for other stars per se, but for their planets, where the resources and landscapes of alien worlds will allow humans to once again take to a planetary surface. In such a case, it is certain that new environmental conditions will be encountered. We will use technology to mitigate environmental selection, of course, but we must remember that we are only just appreciating the significance of epigenetics, the throwing of genetic switches by environmental factors. How will new planetary conditions shape the human genome? We simply can’t say, but we can be sure that it will occur. For example, even the Apollo lunar walkers commented on the lunar soil they inadvertently tracked into their lunar modules; you can bet that they breathed it in. They stayed on the moon only for days…but what would be the effect of such close contact of the human body with new chemistries of different worlds over the course of a lifetime? What genetic switches could be activated in such conditions? We don’t and can’t know; we can estimate and model, but we can’t be certain, and it is likely that selection will occur on our genome again in new planetary environments, at least until we control it with technology.
To succeed in migrating from Earth we are going to have to accept some risk. We do this on a daily basis; in the U.S. many of us take a daily commuting gamble, with nearly a hundred losing that bet—dying in car crashes—daily. If we can take that risk, surely we can adjust to the return of a degree of selection in our dream to colonize space and supply our genus with an insurance policy against extinction or even ‘just’ civilization collapse.
Ultimately, natural selection can be strongly mitigated with technology and is unlikely to strongly structure our genome in the 140-year ‘thoughtscape’ I am currently exploring. But natural selection should not be discounted in plans for interstellar colonization, particularly because it will ultimately involve generations of humanity adapting to new environments.
4.3 The Biology of Interstellar Voyaging: Migration and Drift
Migration is the flow of genes into and out of gene pools (populations) and it is a major factor on Earth, where humans have vast travel networks and today mate even across different hemispheres of the globe. However, in interstellar voyaging craft populations will be relatively fixed (rather than expanding, until new planets are reached), and migration will be between rather small sub-populations of the interstellar craft, an issue returned to below.
Drift, on the other hand, is the result of chance events in the history of a species; a good example, and one most suitable here, is the founder effect in which the genetic composition of a population is strongly conditioned by its founding members. This factor will be of critical importance in interstellar colony voyages because they will be closed genetic systems—as just mentioned—whose genetic structure will be largely established by the founding populations.
Regarding populations, we should take a minute to consider the size of interstellar colony groups. Should we send tens, thousands, millions of people? One way to tackle this issue is to consider our species’ MVP or ‘minimum viable population’, the figure required to avoid the deleterious effects of inbreeding. This figure has been much debated; anthropologist John Moore has suggested a figure of about 150, while others have suggested closer to 500. Such small populations, however, are highly vulnerable to single catastrophes, and my own calculations have suggested an MVP of about 3,000, multiplied by a ‘safety factor’ of 4 to 6 for an interstellar colonization population ‘reference figure’ of 12,000-18,000, which I consider significantly capable of surviving both biological disasters such as disease sweeps and a number of significant technological failures, over the low-centuries figure to reach, for example, Proxima Centauri.
From 12,000 to 18,000 people, then, as a ballpark figure for a founding population for interstellar migration; how do we pick them from the human population? Evolutionary ecologists measure s species’ health by its genetic diversity because a diverse gene pool allows for adaptation to new, unexpected conditions; thus our colonists should be biologically diverse, representing the human genome worldwide (which includes variations adapted to low and high altitudes, for example). However, an over-inclusive approach could endanger future populations if certain genetic maladies are allowed among the founding population. The screening process—determining that certain humans should not and could not participate in off-Earth colonies—seems to go against the very Enlightenment values of equality and freedom at the heart of Western Civilization, but if we are going to succeed in human space colonization we cannot ignore genetics. This is nothing new: over thousands of years human cultures have already devised many and elaborate kinship systems and sexual regulations that prevent the genetic disorders associated with close inbreeding; a survey of Yale’s Human Resources Area Files ethnographic database indicates that most cultures ban marrying or mating between parents and siblings of parents, siblings themselves, grandparents, and first cousins. Humanity has been looking after our genome for a very long time.
The main issue in genetic screening is the detection of genetic disorders that might send a biological ‘time bomb’ into future populations, particularly small and closed populations. But even this ‘simple’ issue includes moral and practical hurdles. In practical terms, this is evident in a depressing poster generated by the federal Genomic Science Program, a rather gruesome document pointing out the location–on each of our chromosomes–of many hundreds of genetically-controlled disorders, from cancers to deafness (we should remember that genes don’t exist simply to cause problems, and that in most cases they build healthy individuals!). Screening for interstellar suitability here seems simple enough: people carrying certain genes would have to remain Earthbound. The significant complication, though, is that while many genetic disorders are known to be simply correlated with certain genes—these are called Mendelian traits—modern genetics finds that more disorders are not so easily ‘pinned’ onto just one easily-spotted genetic marker. Indeed, in a recent paper Professor Aravinda Chakravarti of the Johns Hopkins School of Medicine noted that the textbook concept of simple Mendelian inheritance—’evolution basics’ that I teach in my own classes—seems to be melting away in light of his ‘genetic dissections’ of the real mechanisms of genetic disease, replaced by far more complex models. For example, many disorders are polygenic, the complex result of the interactions of many genes. And, single genes can be pleiotropic, affecting multiple characteristics of the individual organism! To further complicate matters, even though one might carry the gene or genes ‘for’ a certain disorder, environmental factors encountered during the course of life can determine whether or not those genes are activated in such a way as to ‘express’ the genetic disorder.
We must address such issues because, as geneticist David Altshuler of the Harvard Medical School recently noted in the New York Times, “Even if you know everything about genetics, prediction will remain probabilistic and not deterministic.”
And what if we could identify, say, a ‘gene’ for deafness? Just after thirty years of age, Beethoven became deaf; it this were due to a genetic disorder, should he have been ‘selected out’? Should Beethoven’s deafness have been ‘pre-emptively corrected’? He completed much fine music even after his deafness. And what about Stephen Hawking’s genetic disorder, amyotrophic lateral sclerosis? Would screening out someone carrying a certain likelihood of expressing that disorder be a good idea? We already make mate choices, some based on actual or perceived health and future of our partners, and even the fates of some of our embryos. For the health of off-Earth populations, we must be willing engage in these complex discussions to determine what levels of probability we are comfortable with in terms of deciding whether or not a given person can participate in space colonization. Philosophers of morality could be of great help in clarifying the issues in a secular way, and designing real-world solutions.
On the surface, we might think that a solution to these issues would be to encourage the breeding of a master ‘Space Race’, as in the science fiction film Gatacca. But this idea is counter to nature and all of population genetics. If all are identical, all are subject to the same evolutionary ‘sweep’–for example, a single devastating disease. This is why ecologists measure—as mentioned–the health of a species not by its sameness, but by its genetic diversity, which is a well of untapped variation that might provide for a changed future. Any ‘super-race’, then, would be genetically imperiled in the manner of the closely-inbred royal families of Europe, who, according to Dr. Alan Rushton, author of Royal Maladies: Inherited Diseases in the Royal Houses of Europe, have suffered statistically more than their share of genetic disorders.
All in all, from a genetic perspective we have plenty of both moral and genetic reasons to begin studying the genetics of space colonization today. And, critically, we will have to ensure the genetic health of our domesticates and symbionts as well: we will be taking many domesticated plant and animal species off of Earth, some as food, some as companions, some as providers of such things as fibers. A good way to proceed would be to set clear milestones for what we want to know before we can leave the Earth, and work towards meeting them; otherwise, the endless, question-generating process at the heart of science might keep us here too long–and it is only a matter of time before a civilization- or species-destroying event will occur again on Earth.
In the end, if we are going to migrate from the Earth we are going to have to grapple with the probabilistic world of the genome in order to make smart—and moral—choices about the genetic health of our descendants. Regarding the important issue of preserving genetic variability, this could be maintained by ensuing gene flow among sub-populations of the interstellar craft as well as such technological means as carrying along from Earth ‘novel’ genetic material in the form of stored sperm and egg, as well as artificial mutagenesis. All of these measures are under investigation.
5. The Biology of Interstellar Voyaging: Final Comments
Over the course of several generations, as on voyages to nearby stars with propulsion systems that are beginning to seem reasonable, interstellar voyaging is entirely possible from a genetic perspective, with two provisions. First, we will have to ensure the genetic health of the colonist population as it will be under strong founder effect. Gene therapies, carrying genes from Earth in the form of stored eggs and sperm, and even the artificial induction of mutations can all be used to mitigate such effects, but at some point it will cease to be desirable to keep ‘pushing’ a human Earth genome into interstellar space. This brings us to the second proviso, and that is that natural selection will in fact return as a significant concern in human evolution, particularly when the unknowns of new planetary environments are encountered (even if they are surveyed by reconnaissance vehicles first).
We should note that, in the currently-considered timelines and populations, according to what we know about human biology it is unlikely that humanity will undergo speciation in less than a few thousand years (Figure 1, lower right).
These lessons remind us that adaptation is a continual process of the adjustment of the genome to environmental conditions. In non-humans that evolve reactively, with no conscious effort, this equilibriating process is slow and uncentralized and results in many extinctions over time. In humanity, consciousness can be used to help proactively shape our evolution, but we must remember that the only way to stop evolution is by extinction. We should accept and learn from the fact that if things live, they evolve and adapt. We should plan our adaptation to space as students of evolution. We must internalize the truth that the nature of the universe is change, not fixity, and allow this truth to condition our plans for the human colonization of space.
In the next article I will address cultural evolution, and some issues in the coevolution of DNA and culture, in biocultural evolution.
The biological races that exist today will probably disappear within the solar system over the next 1000 years thanks to the enhanced gene flow caused by modern globalization. Current races will, therefore, be eventually replaced by a single homogeneous race within the solar system.
Beyond the solar system, however, new races are likely to be created by the founder populations in other star systems, due to genetic drift. But it would probably take at least a few million years for such semi-isolated interstellar races to evolve into new species.
Marcel F. Williams
Great article. People tend to forget natural selection and evolution does not stop in space. Paul and his crew been busting out great reads! Appreciate it. I’m behind my reading this blog while traveling. Best blog on the internets. Thanks Paul and crew.
I enjoyed this article from Dr. Smith, although must admit I was hoping for more speculation on types and progressions of useful mutations and adaptions for our prospective travelers. SF authors have explored these ideas in fiction, but its hard to judge which of their many imagined changes would be realistic and likely, rather than just being very entertaining to read. Perhaps we can look forward to deeper analysis of the selection pressures of deep space travel and projection of likely adaptions from Dr. Smith in his forthcoming works.
The article today emphasizes potential genetic bottleneck effects, but as commented by Geoff to an earlier article this week, “…DNA is effectively just information, which can be transmitted at light speed.” Additional genetic variety can be easily received or carried with colonists as data and introduced through gene synthesis and manipulation of zygotes. Only slightly more onerous would be bringing frozen zygotes sampled from a much larger population as mentioned in today’s article. So a population of hundreds could breed with a “stored” population of thousands or even millions of individuals, screened to avoid serious disorders. And through gene recombination, the stored sample pool could be permuted in nearly infinite variety.
This all assumes, of course, that the stored information/material and supporting technical tools survive and the knowledge and willingness to use them exist among the colonists. But I think this is a fundamentally easier hurdle compared to the difficulty of achieving significantly higher speeds at an affordable level of energy expenditure, withstanding drag/impact radiation/erosion from sparse interstellar materials, and beating back the general affects of entropy making things fail over time.
I always think that the most important thing in building worldships is to provide the inhabitants with generalized tools and resources that they can use to inovate solutions to whatever they encounter. Certainly trying to identify possible problems and solutions ahead of time is important, but I see it as much more important to give the population as much flexibility as possible to deal with unexpected problems.
In regards to the genetic aspect covered in this article, I would think the ship should have as large a gene bank as possible, representing as much diversity of all life forms of Earth as possible, and the tools necessary to use it, so the population has the most resources possible to solve whatever problems they may encounter during the voyage, or at the destination.
I would also think that with such resource flexibility the minimum necessary population size would be reduced, as there would be significantly more potential diversity in such a population + gene bank than would seem apparent in a simple population count.
This reminds me of an SF story I read years ago where Mankind had spread throughout the galaxy for 100s of thousands of years at sublight speed, establishing colonies which in turn sent forth further expeditions. However, Mankind never came across an intelligent alien species until one day at the opposite end of the glaxy from Earth, they met a strange biped species whose bizarre appearance and strange culture rendered them almost incomprehensible. While struggling to understand this new lifeform, an analysis of their DNA showed them to be human. It seems that they were the descendants of humans who had migrated counter-clockwise around the galaxy, while their dicoverers were descendants of humans who had migrated in a clockwise direction. In fact, their discoverers had also evolved beyond recognition from their human origins (which was the story’s double twist ending).
Cameron M. Smith:
Please consider including a chapter on In Vitro Meats in you future books. Including livestock may not be necessary on future worldships…Let’s hope so…Unless the goat or pig is traveling as a true pet….We are all part of the animal kingdom….James D. Stilwell
This issue becomes moot if we use the most cost effective (if slow) means of colonizing the stars – sending frozen embryos (humans and even animals and plant seeds). Millions of embryos can fit in a container the size of a steamer trunk, making shielding easy and greatly reducing the size of the payload and life support needs.
Upon arrival at a suitable planet, the ship activiates a battery of artificial wombs and brings the first genration of colonists to term. Once born, they can be raise by robot parents who appear to be human and have been program to nurture, teach and protect their human children (the programming can even simulate “love”), until the first generation of colonists have grown to adulthood and can be parents themselves.
I would suggest that bio engineering, rather than natural/artificial selection and genetic drift, would more likely be the dominant driver of human evolution by the time we start serious star faring, or even colonizing the solar system in habitats. Which is not to say that evolution will stop, it won’t, but it will act on the engineered humans.
But remember, evolution requires modification with descent. As M Lockmoore states, a computer selecting genomes from a vast database would short circuit the descent part of the algorithm and eliminate evolution.
Yes, great reads this week.
I’m thinking that the author wisely takes the long view about evolution and surviving. But I imagine many worldships will not be populated along rational or reasonable sortings at all, but rather ships-of-fools. Over the next thousand years, I can easily imagine many ethnic ‘Exodus’ worldships heading out. And political refugees, religious cliques and wealthy eccentrics will invest in colony ships as soon as they are possible. And some of those sub groups will evolve in a narrow way.
Andyet, you write suspiciously like Star Trek’s “Q” would write…thus making the concept of the worldship oh so pointless….
Just kidding….Doubt if “Q” even bothers to write e-mails…
Or whatever…JDS
This a subject for another day, when I have hundreds of spare hours to elaborate the concept (post retirement?) …
However, the proper way to think about space arks is as organisms, with the structure, electronics, and humans as bones, nerves, and muscles. If space arks, like Larry Niven’s starseeds, are to be viable, they must be able to have a sustainable metabolism in the space environment which permits locomotion, repair, growth, and reproduction. It is the “biology” and evolution of the space arks which is most interesting.
There are only two significant sources of energy for space arks, stellar energy and controlled fusion. Niven’s starseeds were stellar powered for both metabolism and locomotion – going dormant while in transit. Most people in the interstellar community seem to assume that human space arks would be fusion powered for metabolism and locomotion, and kept warm and active in transit. However, from the point of view of the ark as organism, if it is not feeding, growing, or reproducing, shouldn’t it be sleeping to conserve energy?
Fascinating post!! Seen in this light, interstellar migration is an entirely natural development of the human species’ continuing effort to adapt to strange environments.
I hope that forthcoming posts will discuss the social environment of a multi-generational starship, the authority structure, and what freedoms the crew may lose on the voyage. What sort of leadership would be best on such a voyage- a military style command structure, or a community democracy model, or something else? Will a crew member’s choice of profession be limited because certain positions on board have to be filled? Will you be limited in who you can marry by genetic considerations? If stored sperm and ova are carried on board to ensure genetic diversity, who chooses when and how to use it? Will women be required to have “duty children” from such stored genetic material even if they would rather not? And, can we even hope to plan for all contingencies on a decades-or-century long voyage during which command structures could be replaced and society possibly change considerably before the destination is reached?
A paper I found at the NASA technical reports server titled “The Centauri Project: Manned Interstellar Travel” makes mention of the social environment of interstellar spaceships, and also suggests we design a craft that is basically a wandering mini-planet.
http://ntrs.nasa.gov/search.jsp?R=19910012846
Hello, all — thanks for your interesting comments. I agree that technology will be used to mitigate many genetic issues, and I also have considered artificial mutagenesis to introduce variation — Earth mutations observed while the craft is speeding away could be sent up to the craft by radio. But at some point, pushing an ‘Earth-normal’ genome off-Earth won’t pay off (not sure if I mentioned this or not and have done too much reading today to go back and look).
I will be investingating all of this in greater detail in a technical book I’m now working on, on these issues; my 2012 book (noted at the top of the blog) is more popular science and casts a very wide net.
Thanks again,
Cameron
I like the way that Cameron Smith is prepared to work with the complexities of the real world, rather than through a massively oversimplified toy model. Unfortunately, I fear that it is still to simplistic.
Smith talks of our typical K selection being still in play. Today, one of the strongest drivers of this should be sexual selection, though contraceptive failure may be even more important (such as explaining why career criminals have so many children). This trend may be accentuated by in vitro gene selection. May I point out that height is one of the most robust measurable indicators of sexual attraction, and that this is limited by Earth strong gravity. I posit that Martians would soon be very much taller than their stay-at-home relatives. This would create very different fashions, and ideas of beauty that uphold sympatric speciation even against a very high influx of “ugly” Earthlings that no one wants to mate with.
However, ever since I noticed something very strange, I have worried more about the much high r type selection pressures. In humans this only occurs with sperm finding eggs. Even though it is much stronger than K selection, for most traits it should be limited by having two haplotypes (the main exception being Huntington’s like situations where gene copy numbers frequently vary between generations). Now, in the Palaeolithic, any such genes that had a a pleiotropic effect in hastening sperm finding the egg, but with a deleterious effect on the adult, would have long ago achieved an equilibrium. Since it is against a K type strategy this would have to have an incredibly efficient mechanism at removing those genes. The problem is that I think I noticed one: large head size killing mothers during delivery. Could this explain the Flynn effect and an exponential rising caesarean rate since the advent of modern medical care?
Ok, that specific example was all way to speculative, but, I believe, not the idea that genetic changes might occur much faster than you posit, even without Gattica-type parental in vivo selection.
Also, as other have pointed out, sending frozen sperm/embryos seems such a mature technology today, that it is hard to envision our descendant worldship builders not utilising it, let alone de novo gene synthesis technology, which should also be mature by that time.
It is just a matter of time before we have intersteller voyages. Look at how we have progressed over the years. The things we can envision today is our hopes and dreams for tomorrow. The “Space Arks” and space travel becomes more of a reality each and every day. It’s just a matter of time.
I found this article disappointing because it doesn’t embrace the stellar (heh) advances in biology/chemistry happening today, nor project any impact on future phenotypes. It seems a common error that futurists predict advances in their area of expertise, leaving out exciting vistas of other arts/sciences. That “the principles of evolution are largely intact” has little relevance to the subject at hand. For example we are well into cyborg technology at present. If we can jettison today’s false notions of morality and ethics foisted upon honest thinking to gum up the works, then the man/machine union will consummate and the stars are ours forever. Yes, we’re talking genetically-encoded USB ports…erm, make mine Wifi.
Speaking of ethics, people…paaaleeeese …Think it through. Leave the farm animals and outmoded notions of nutrition and agriculture on the home planet we’ve just ruined, shall we? Only vegans allowed to fly on this silver seed to a new home in the … stars.
This article led me to ponder the fate of the International Space Station ISS; I think that we deserve to see some return on our $100+ billion dollar taxpayer investment. Lets capture the public’s attention; First, send a (very healthy) astronaut couple into space for a year and a half, with the right doctors , with the expressed purpose to procreate and birth a child. Imagine the positive publicity! Next, or while we are at this, make the required alterations so that at least one module can spin up to create (some!) artificial gravity. Add another module devoted to an reasonable attempt at closed cycle air-water etc. Last, before the ISS burns up in re-entry, make the modifications and strap on a booster to send the thing into high lunar orbit. We get a base; a stepping stone destination to send people, a resupply depot. Stretch goal; boost the ISS to a slow transfer trip to Mars, after adding sheilding, structural modifications, more modules, etc, a crew of a dozen or two, plan on the trip taking years.
“Millions of embryos can fit in a container the size of a steamer trunk, making shielding easy and greatly reducing the size of the payload and life support needs.”
That is a very good point. Like suspended animation, it depends on a technology not yet mature- artificial wombs.
It is a great plan except it does not include me going along.
“-I can easily imagine many ethnic ‘Exodus’ worldships heading out. And political refugees, religious cliques and wealthy eccentrics -”
Considering the energy needed for any mission to another star, the situation on Earth will, IMO, greatly improve concerning the human condition by the time we can generate such power.
I have not read of any practical plan to provide enough energy for a western lifestyle to 10 billion people except David Criswell’s Lunar Solar Power. He presented this concept over a decade ago and there is still no alternative.
http://news.nationalgeographic.com/news/2002/04/0426_042602_TVmoonenergy.html
The tremendous energy available by beaming energy from the Moon is also a possible source of propulsion for star travel.
Eric’s idea of boosting ISS to Lunar orbit as a permanent staging base is a good alternative to that of all Earth’s people watching it burn on re-entry. Too depressing.
Add shielding. Boost it out. Instant Lunar base. Start prospecting for water deposits.
This is an amazing post. A very complex scientific issue involving all possible human scientific fields of this era and the future. I guess that planning this trip to the stars, we need to have the clear goal: having the most diverse possible gene pool arriving in the new planet. But not just diverse, as mentioned in the article. A balance between adaptation and adaptability needs to be found using all possible genetic tools we may develop until then. Speciation in humans can take only a few generations if the founder effect is too strong. Mayr calls this kind of speciation “genetic revolution”. This can be a risk factor that has to be avoided? Is the right tactic to plan genetic change as much as possible, or letting evolution flow? We have 1mil. years to find out before the sun will mature. Or maybe much less if we consider our footprint on the planet. Great story!
@Gary
Lunar solar industry sounds fine but Lunar H3 fission power industry sounds good too. If we can get it working in Earth first.
Arkships- It takes much less energy to simply escape the Solar system in an ark than it takes to actually accelerate to another star. If the ark is your life, it doesn’t matter whether it takes 3 generations or 300 generations.
This has been a somewhat unrealistic discussion , asking only what would be best and not what would be afordable . If human beeings ever dare to travel to another star , they will do it in the cheapest possible way ( which will also be incredibly expensive) , and that means that any other considerations will be secondary to economics .
From the point of view of economy , human biology , evolution and genetics are just another obstacle to be overcome in the cheapest possible way . The solution must be to search for the minimum size of creew capable of surviving for several hundred years using any ”dirty trick in the book” so as long as they are capable of maintaing the millions of frozen embrioes which are the REAL creew of the ship . Theoreticly it would be enough for 1o female humans to start up a new population whith a reasonable genetic diversity , if the embryoes can survive for several more generations . It would demand that every woman had several children born from geneticly different embryoes. The ability to maintain human embrioes for long periods are therefore extremely important starting from NOW . If we want a record of 300 years of sucsesful maintenance of embryoes before starting on a 300 year long voyage , this record might be a crucial limiting factor long time after other tecnical problems have been solved . This ablity is the key to a drastical reduction in the cost of any realistic starship . For 10 or 20 generations the ”live” crew wil mostly have children which are not biologically their own . Their own bilogical children can be added to the embryo bank .
I don’t understand this:
“figure 2 indicates that even in recent times, civilizations have repeatedly collapsed and disintegrated, with no guarantee of recovery..”
Taking the world’s global civilization this is a false characterization.
Especially in Western civilization.
In one fashion or another the unique enlightenment of Greek civilization was never lost. It’s enhancement by the Renaissance would have happened sooner or later.
Of the ‘advanced’ civilizations, take Western Europe, after the fall of the Roman empire Human civilization DID NOT collapse back to The Neolithic Period. The Dark Ages were pretty grubby but not stone age.
In Western Europe learning and the level of civilization was slow and grubby but agriculture and the start of urban civilization was one overlapping sequence.
In the model of global history starting 10,000 years ago (that being the mystery moment) it has been a steady , if sometimes uneven, advance towards a complex technological society.
Where we go from here can only be speculation.
“for the past 23 continuous years human beings have already lived off of the surface of the Earth in various orbital stations” — sorry, Dr Smith, not quite. There was a 7-day hiatus, with nobody in space, between the landing of STS 92 and the launch of Soyuz TM-31, the latter carrying the first crew to the ISS on 31 October 2000. The current period of continuous human presence in space is therefore 12 years and 4.5 months.
Stephen
What strikes me about this article is that you envisage the interstellar expedition departing specifically from Earth, not from the broader Solar System, and confining its targets to planetary systems which contain an Earth-analog planet. This implies that you envisage a breakthrough in propulsion technologies and costs. Do you have a specific breakthrough propulsion system in mind, or are you simply assuming that past trends in the increasing speeds of transport technologies will continue?
Stephen
I think the speed axis in figure 3 needs correcting. Unless my math is way wrong, the time taken to travel ~ 4ly at 0.03%c is nowhere near 140 years. 3%c yep, or just lose the % symbol.
Very interesting article, thanks to the author and Centauri Dreams for posting it.
———————————————–
” Millions of embryos can fit in a container the size of a steamer trunk, making shielding easy and greatly reducing the size of the payload and life support needs.”
———————————————–
Could someone, Paul Gilster or Cameron Smith or a DNA expert, comment on this. I have some issues with this.
One of the most effective drivers for DNA mutation is cosmic radiation. Cameron Smith is pointing in the article to this as possible lead for brain disorders. We all know cosmic radiation reaches Earth and biosphere. We don’t know how cosmic radiation affect Nature but we can clearly find evidences in tree rings, rocks, and soil. The LNT (Linear non-threshold) model has a major gap at very low raditon levels. It is even assumed that radiation is essential for humans as no or very low radiation is as lethal as high dosage.
When we talking about embryos as backup for genetic diversity the default assumptions is they are unaffected. In space cosmic radiation is abundant. As far as DNA which procreate itself carries the necessary mutations, thus adapting to changing environment. Embryos in deep freeze are open for same cosmic radiation except the impact it has on DNA are not adaptational, thus instead they become corrupt, which accumulates over time.
In Vitro Fertility success percentage is no more than 30%. A woman can’t have more than 2 IVF sessions per year. Success of IVF is low, for this reason more than one fertilized egg is planted. The standards how many currently varies significantly around the world. In Europe more than two is not professioanlly accepted and in case of twins it’s considered a failure. There is no guarantees IVF would ever work, meaning a woman could go trough IVF sessions years (3-10 year in a row) w/o results.
1) With low IVF outcome probability, possible DNA damage due to abundant cosmic radiation would embryonic reproduction of World Ship population considered as a seroius risk? 2) How well the embryonic reproduction is actually thought through?
I don’t think humans can survive zero-radioactivity environment or very effectively shielded (artificial) environment.
We actually know very little how the interstellar cosmic weather affects life on Earth but it does in significant way – cosmic radiation is the sole reason why airborn aerosoles get excited and they in trun are the reason why clouds form at all. Stars far away do die and they do affect Earth w/ their cosmic radiation.
Great article.
One quibble, though: I find the notion that “the principles of evolution are largely intact” very quaint. Whatever artificial environments, high living standards, and intensive medical care have already done (or not) to dismantle natural selection will be utterly dwarfed by what genetic engineering is going to do to random mutation. What will result from this is hard to predict, but I feel safe in postulating that it will look about as different from natural evolution as a modern engineering design firm does from a primordial swamp. “Largely intact” is certainly not the term I would use.
Of course, as many have already pointed out, and you hint at yourself in one sentence near the end: Genetic diversity is NOT a factor in determining the optimal crew size, because the diversity can be very easily carried as frozen gametes. As others have pointed out, the optimal crew size might even be zero.
I do like your thoughts about taking care to avoid genetic defects by careful selection. We do want to send the best genes we can find on Earth. When the time comes, it will probably be possible to put those best genes into whatever crew is selected by other criteria (and the gametes, of course), resulting in less onerous moral issues. It is less objectionable to select genes directly rather than selecting people for their genes, or is it?
@Eniac
Genetic engineering uses the model of modern evolutionary biology as the foundation of construction at the molecular level of the life sciences.
There are many debates as to what will constitute a successful colony effort.
Considering the number of factors that drive humanity, the interstellar travel problem may not require a natural selection issue? the late Arthur C. Clarke had a brilliant and simple response; ‘We gave up evolution to our machines.’
Trying to replicate the ‘natural’ by artificial means is in itself just a philosophy.
Interstellar colonization is a ‘cultural’ effort; but seeing how things are in these debates… leaving our solar system will be people who are far different than the average ‘walmart & food court shopper’.
Dmitri writes:
I’ll leave this one up to someone more qualified. Dr. Smith should see your question soon.
Having written a paper on the embryo option, I can see a lot of unknowns that will need extensive experience in a range of technologies, both biological and robotic.
My preferred option is full-body rebuilds from data, but that’s even more speculative than raising embryoes. Alternatively we learn how to lock up the molecular structure of bodies, much like brine shrimp or tardigrades when they undergo cryptobiosis. Goddard, way back in 1918, proposed we breed a crew that can undergo reversible mummification – essentially cryptobiosis.
A. A. Jackson: I am mystified by your comment. While I do not understand your point, let me try to clarify mine:
Modern evolutionary biology is the foundation of understanding how life could develop through the complex interplay between inheritance, random mutation, and natural selection.
Genetic engineering is the targeted modification of the genome based on understanding of the mechanisms that underlie biological function. It has, in principle, little to do with evolutionary biology. I grant you, though, that often understanding how something developed can be helpful in understanding how it works. And, of course, the tools of genetic engineering are, opportunistically, mostly those that life has “evolved” for us, rather than of our own construction.
My point is that the targeted and deliberate nature of genetic engineering makes it entirely different from random mutation, and my hypothesis is that this will utterly change human evolution into something completely different, something no longer accurately described by that name.
Dmitri:
I do not think this is a common assumption, and I think it is baseless.
1) Frozen gametes or embryos would be protected by shielding to the extent necessary to reduce radiation induced damage to the required level. Indications are that this is not a very hard problem. 2) Thought through enough to be practiced routinely in IVF clinics, as you yourself have mentioned. Not sure I understand your question. It may be the process is tedious, but the benefit that comes from a genetic population of millions that can be taken in the volume of a steamer trunk far outweighs the inconvenience.
I do not believe this is true.
How exciting and interesting it is to read about interstellar travel from a biological perspective, as it is true that the topic usually gets discussed purely in terms of propulsion and engineering.
Would a hollowed out asteroid provide enough shielding to adequately protect the would-be colonizers from the harmful effects of myriad cosmic radiation as they make their way across the light years? I am speculating the answer is yes. After all, dark matter hunters are currently taking advantage of rock shielding here on Earth to filter out sources of cosmic radiation with the idea being that just about any extant signal is likely to be some sort of non-baryonic weakly interacting particle that did what run of the mill baryonic particles could not—non-chalantly penetrate meters of solid rock.
Looks like someone has already looked into the issue and found answers. Low- and micro gravity does affect in a way we don’t want to. All in all more insight into this would be greatful and I’ll keep eye on Dr. Anja Geitmann’s researches.
http://phys.org/news/2013-03-hyper-micro-gravity-affect-involved-reproduction.html
The research paper with all the details is here:
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0058246
@Eniac
To quote:
“Genetic engineering is the targeted modification of the genome based on understanding of the mechanisms that underlie biological function.”
This true , but “understanding of the mechanisms that underlie biological function”, comes directly from the modern model evolutionary biology, which is the foundation of all modern biology.
Without the existence of the modern model of evolutionary biology*… genetic engineering is dead in the water.
*(In particular modern evolutionary molecular biology.)
A.A. Jackson, your descriptions of biology seem increasingly strange. As far as the model that underlies biological self-replication and protein synthesis is concerned, it would be more accurate to source it as emanating from von Neumann’s mathematical descriptions of how and artificially created self-replicating mechanisms might work. Even that would be a poor description though.
Biology is complex, and more than just evolution. To me, IF there is any strong connection here to GE, it is how Darwinian evolution is now honoured in the breach. Because GE can ‘tunnel over’ any deleterious intermediate forms, evolution may collapse to the type first envisioned (before Darwin!) by Buffon, where the final form of unrelated lines tends to converge to a single morphology for each particular niche.
I am sure you know that much of our knowledge about biological mechanisms comes from painstakingly researching the individual components, isolating proteins, running lots of gels, etc, etc. Understanding evolutionary biology helps, but it is not required to understand how existing organisms function.
You can understand and fix an automobile without knowing how an assembly line works. Most auto mechanics probably could not tell you the first thing about production facilities, but can fix your car just fine.
This is all beside the point, anyway, because genetic engineering does exist and will have the aforementioned effects, whether it relies on evolutionary biology or not.
@Eniac
“2) Thought through enough to be practiced routinely in IVF clinics, as you yourself have mentioned. ##Not sure I understand your question.## It may be the process is tedious, but the benefit that comes from a genetic population of millions that can be taken in the volume of a steamer trunk far outweighs the inconvenience.”
My issue with embryonic offsprings in space via IVF is:
a) every IVF brith is a miracle
2) every IVF procedure is heavy stress on female reproduction organs
3) each IVF prodecure has social+psychological implication on relation / marriage due to vexed sexual life
4) DNA self-repair mechanism is a key factor mitigating radiation related damages (as Dr. Cameron Smith pointed in the article)
lead to the notion that w/o Earth’s protective atmsophere and magnetosphere the frozen DNA degrades over time and introduces bigger risk of uncontrolled DNA mutations to the insterstellar ship crew. The natural way of procreation passes DNA self-repair information to offsprings which with each generations becomes more resistant to space radiation and interstellar wheater. Instead of being an insurance for pure, unaffected DNA frozen gametes or embryos hide more serious risk – more like gambling rather than sound idea.
————————–
#
“It is even assumed that radiation is essential for humans as no or very low radiation is as lethal as high dosage.”
I do not think this is a common assumption, and I think it is baseless.
#
BBC Horizon made a documentary in 2005 Nuclear Nightmares. They discuss about radiation, health hazard and LNT. LNT claims that probability of dying by cancer due to radiation is 10%@2000mSv, 8%@1500 mSv , 6%@1000mSv, and 3%@500 mSv. There is little or virtually nothing known what is results at 100-200 mSv or below 100 mSv. Due to linear nature of LNT graph scientists have deducted it will gradually go to zero or have little bumps / ebbs. In human history there are only a handful major nuclear events which could server as a basis for data collection and statistical analysis – Hiroshima / Nagasaki, Chernobyl and now Fukushima. In the ecavuation zone of Chernobyl the radiation level is still at 10 mSv. All sorts of animals live and thrive there now. The animals receive 8-15 mSv daily. A commercial liner crew receives 36 mSv / year @ 35000 feet (1100 x-rays a year). The actual casualities of nuclear disasters are much lower than LNT predicts. In ’70-73′ US made a study on cancer emergence which showed that the cancer rates where much higher in regions with low radiation levels compared to who populations at much higher radiation levels – mountain regions at height of 1 – 3 kilometers. The most controversial claim of the documentary is that moderate levels of radiation is benefitial to the health. In the same time it’s the most thought provokive especially after Fukushima disaster which is either on par w/ Chernobyl or greater. The defective cell ratio on rodents captured in the Chernobyl radiation zone was less than on rodents captured on normal or low radiation level zones. Just the cells which are responsible for mitigating the defected ones (cancer cells) were much more active and present.
We know virtually nothing what radiation actually does and how we cope in high or in no radiation environemnt. The uncharted lower area of LNT is for some scientists the indication that radiation is essential for human survival and no-radiation zones are as lethal as high radiation ones.
Now there is a huge difference between fully developed born offspring vs embryonic one in radiation environment. What I try to challenge is how likely in the discussions here we take the embryonic approach as best source for mitigating DNA mutations. I feel it serves contrary.
BBC Horizon: Horizon: Nuclear Nightmares (50 min) http://www.dailymotion.com/video/xwy1o5_bbc-horizon-nuclear-nightmares-2006_tech
—————————
#
“cosmic radiation is the sole reason why airborn aerosoles get excited and they in trun are the reason why clouds form at all
I do not believe this is true.”
#
It’s not my claim – it was made by NASA scientists. Thanks to Henrik Svensmark’s percevierence on his theory of Cosmic Rays and impact on Earth climate his theory is not just accepted but in CERN there is project CLOUD which is doing experiments w/ aerosols to precisely model and measure atmospheric impacts and cloud formation mechanism by bombarding X-rays.
* Cosmic meddling with the clouds by seven-day magic – http://phys.org/news168353215.html
* A Danish documentary on his work and how it was recieved, struggels and results (52 min) – Svensmark: The Cloud Mystery – http://www.youtube.com/watch?v=ANMTPF1blpQ
Dmitri: It is possible that no radiation at all is slightly less healthy than natural radiation levels, although unlikely. “Lethal”? That just does not make any sense.
Same with the clouds. There may well be a detectable effect of space radiation. This is reasonable and even expected. But “the sole reason”? That would overthrow everything that is known about cloud nucleation.
@Eniac, I’m with you. It didn’t come easy for me either. Took significant time to sink in. Just during that noticed other related information which correlated with the notion.
Lethal, as synonomy for “certain death from high exposure” should be substitute by “with as high mortality rate as”. That actually makes sense as low or no-radiation does not kick in th DNA repair mechanism which in turn does not mitigate DNA damages and contributes complications w/ higher premature sicknesses /deaths.
AFAIK cosmic ray theory does not contradict or refute cloud nucleation. Cloud nucleation is a physical process not chemical. The mechanism goes somehting like excited aerosol attracts airborn impurities which in time grow and stick with water wapor droplets growing further and seeding cloud formation. For the discussion the process per se is not importat. I used it as an illustration for show cosmic rays do reach Earth and impact people and atmosphere. In space cosmic ray does not any obstacles, thus having no problems alter biological substance. This plays in hand for formation of microbes on ice dwarfs or comets.
Pondering on embryonic offsprings and this knowledge felt urge to hear a specialist opinion on the subject.
Well, if I already touched the cosmic rays and aerosols, there is an article and video of CLOUD results and what they do – http://phys.org/news/2011-08-cern-cloud-team-pieces-puzzle.html
The same thing clicked in my mind when turned out earth is proably at the very edge of HZ. Clouds then have play crucial role on sustaining climate and environment for living organisms and not just on Earth but on other planets / moons.
Quick additional thought: To ensure genetic diversity, it is actually sufficient to take male gametes (aka sperm) only. Not only are they even much more compact to transport than eggs or embryos, they are also much easier to obtain and administer.
Worst case you lose some mitochondrial diversity, but I do not believe that would be a problem. Those are not particularly diverse, anyway, being haploid.