I had the idea for a group of advanced humans using technology to rework their bodies so that they lay eggs instead of giving birth to live young, just like a platypus (possibly to survive in an alien environment).
What kind of advantages would laying eggs provide?
I could see this being a "great idea" some scientist has as a solution to the "problem" of pregnancy for those colonizing planets. The reasoning would be that the women would lay the egg, pop it into an incubator, and then get back to the important work of helping build a new colony. Plus, they wouldn't have to worry about the menstrual cycle anymore! (Or would they? Which sounds worse to you - a period or having to lay an egg every 28 days?) You could have it be something only one group of colonists try because "why would we ever doubt the charismatic man in a lab coat? I mean, he's a scientist! He's got to know what he's talking about, right?" So the women let him tamper with their bodies in the name of "science!!!" And then they come to learn that having to lay an egg instead of wearing a pad isn't all it's cracked up to be.
Ooooh, bad choice of words.
There are very few situations I know of where it would be useful to lay eggs. Why do I say that? Well, evolutionary speaking, we see transitions from egg laying to not-egg laying, but only a handful of cases where it might have gone the other way, if any.
Fundamentally, laying an egg requires one to provide the resources one needs for a fetus to come to term. It requires the maximum expenditure of resources, because you can't add proteins or calories to an egg after it is laid. You have to give it everything it could possibly need. On the other hand, with live birth, you only have to give it what it actually needed.
The one thing I could think of that might sway this behavior is if one lived on a planet which was immensely hostile such that you need every able body working in order to survive, but you could create some "safe havens" where one could nest. In that extremely unusual environment, it might be convenient to be able to lay the eggs and then continue working. While plenty of women do indeed keep working while pregnant, and there are stories of slave women giving birth in the fields and continuing to pick cotton, it's clear that is a less than ideal solution. Freeing one-self from the fetus quickly would be beneficial in those cases.
None - but there are a lot of disadvantages...
Carrying the fertilized egg until gestation is intrinsically self-protecting and allows the carrier to act without being substantially tied down.1
Any duck can tell you that keeping track of the brood is a pain in the neck.2
You need to keep eggs warm, but living in areas with hot sand is a non-starter for me, and feathers aren't her style.3
Watching anyone turn your children into breakfast would start entire wars.4
1 My wife suggests that I know a lot less about what I'm talking about than I pretend to know, but she concedes that not having to sit on a nest 80% of the time is useful when she wants dinner and a movie.
2 Yeah, she thinks this question is silly. We don't have twins, but we know people with twins and people with kids born but 9 months or so apart, and their lives reek. They reek like spoiling pomegranates. Kinda sweet, but in the end, you have to throw it away. (Don't get me wrong, none of them would trade their kids for the world, but when cornered about the issue, none would disagree that broods are committed-time-multipliers.)
3 She won't wear feathers and while we're getting older and warmer climates are becoming more interesting, when we think back on our 20s, that wasn't happening. Nope.... high altitude and cold weather for us, thanks.
4 She agrees with this, but thinks I'm starting to stretch for examples of why this is a bad idea and is politely suggesting that I'd be less of an idiot if I quit while anyone might think I was ahead.
Advantage? None, I would say.
Each egg needs to be large enough to hold a full-grown baby, just before it emerges. Which means a female will have to grow a baby sized egg inside her body, then push it out without breaking the egg.
But human females have eggs 'ready' about 12/13 times a year, for about 40 years. There isn't much to gain to have females produce hundreds of huge eggs in a lifetime of which only a handful will be fertilized. What will you do with the unfertilized eggs? Make omelettes?
In Edgar Rice Burroughs's book A Princess Of Mars, the martian people did lay eggs. They put the eggs in an incubator and under the influence of sunlight they grew for 5 years before the children hatched out.
They must have been getting CO2 and water and nutrients, and photosynthesis let them grow. So they started out a nice reasonable small size when laid.
Burroughs strongly implied that the women had human breasts, and it looks pretty clear that the babies didn't get milk from them. The reason for these is left as an exercise for the reader.
It looks like a good thing if you can do it. Be pregnant for say 4 months. Lay a small egg. Let the incubator do all the work for the next 5 years until your child reaches an interesting age. But it needs the photosynthetic eggs, and it needs the incubators.
In his story the unhatched babies were telepathic and they learned a whole lot about society before hatching so they didn't need to get taught a lot of the things we teach small children. I have no idea how to do that, but I'm sure society would be wildly different if small children got to listen in on all the adult's thoughts for 5 years before they ever got involved, and parents never got any chance to lie to them. Right offhand I expect they'd hatch out extremely cynical compared to us.
The biggest problem might lie in the actual process.
As I understand it, egg-bearing creatures need a lot more DNA information than live-action childbearing ones.
Since the egg is in a semi-controlled environment (some egg that lies somewhere) instead of a fully controlled one (mother), the egg creature needs a lot of extra plans for temperature changes and other external changes.
Making a baby in the mother only requires a recipe, the environment takes care of all the rest.
Would probably make more sense to just incubate the babies and grow them in a tank than to try to change up humans to lay eggs
You're not likely to see any benefits, at least none that outweigh the problems involved.
Size
A mundane problem, but a serious one. Humans already have notable difficulty giving birth, and large babies cause particular trouble; some mothers die in childbirth even with modern technology and medicine, and in pre-industrial times that rate was significant. An egg that must ultimately contain such a baby is guaranteed to be even larger (unless you want smaller and less-developed babies, thus effectively premature babies, which poses a host of issues like much higher rates of infant mortality and mental problems) due to the need for the enclosing eggshell if nothing else, never mind any nutrients or other materials that might be left over. That makes all those potential complications more likely and more severe.
I don't want to see the consequences of trying to give birth to a baby that is unable to fit through the birth canal; that would be a common cause of death for egg-laying humans without other drastic changes. Widening the birth canal may seem to be an obvious answer, but the design of human hips is a compromise between walking upright and giving birth; a wider birth canal, especially to the required degree (probably at least 50%, because the egg has to hold a human baby and have a shell thick enough to offer actual protection), could seriously impair a woman's ability to walk on two legs.
Protection
Animals that lay eggs and abandon them do get to scatter many potential offspring, but most of those eggs will be smashed. This is a viable strategy (see R-selection versus K-selection), but that is not conducive to anything resembling civilization. Animals that guard their eggs, on the other hand, have one parent basically glued to the nest from laying to hatching (which would be months for humans); the care this requires does reflect the possibility of intelligence and civilization as we recognize them, but that puts a heavy burden on whoever is not tending the nest.
Pregnancy and live birth, by contrast, make protection relatively trivial. It can be seen as carrying the egg or eggs within the mother's body instead of leaving them outside it, which reduces the problem of protecting the offspring into simply having the mother protect herself, something she would be doing anyways and thus is not an added cost. It also saves the expenditure in energy and materials of creating the eggshell, another point in its favor.
Hatching
How, exactly, is a human baby going to crack open an eggshell from the inside? We are born rather weak and frail, without any convenient sharp claws or the like. Our skulls are still very fragile, so breaking out with any hypothetical added appendage to the head (a special tooth or horn that falls away after hatching, most likely, but I'm open to suggestions) is going to involve a lot of battering against the shell from the inside, likely causing permanent brain damage. Keep in mind that larger eggs are naturally going to be thicker (read: harder for the baby to break open), to offer more protection: too thin, and the weight inside would crack it just from falling the few inches between the mother's body and the ground.
Besides, on hatching, they're still going to be helpless for a very long time. Many egg-layers have offspring that is at least mobile within a few days; if you want your humans to match that, their offspring will have to undergo significantly more development before hatching than normal humans do before being born, which requires a larger egg to hold the larger baby, which in turn feeds right back into the size problem! Also, there are studies that suggest our level of intelligence requires a long period of effective helplessness while our brains develop and learn, whereas species that are born with more development are also more limited in learning capacity; I can't prove this point, and you could probably get away with ignoring it, but it's still something to consider.
Conclusion
Egg-laying works for some species, but bipedal intelligent humanoids would most certainly not be among them, at least not in anything nature might produce. You say that genetic engineering is involved here, removing the question of evolution, but you'd still need a reason why they would do such engineering to change humans to what (for humans) gives every sign of being an inferior mode of reproduction.
If laying eggs is easy work and not too painful, then I'd say this is definitely beneficial.
Being pregnant is hard work. Morning sickness is like having food poisoning every single morning for 3 months, and some ladies stay sick all the way until birth. Not to mention painful stomach cramps, etc.. That kind of stuff can make it very difficult for a woman to maintain her job during pregnancy, too.
Other than the effort to produce eggs. One downside I can think of is the emotional impact. Pregnancy also has a slew of hormonal changes associated with it, which tend to emotionally bond the mother to the child prior to birth.
More experimentation is needed, but I could definitely see some advantages in terms of comfort and productivity.
There are a some benefits that humans could gain from egg laying. They could populate new areas by leaving their eggs there. They could also mix cultures, simply by leaving their eggs behind while traveling. Their culture may also benefit from the rich experiences gained through a brutal childhood. However, these humans would need a few additional enhancements:
Their eggs need to be able to hatch unattended.
If human's eggs were similar to insect or fish eggs, they could leave their eggs to hatch unattended. This would free the adults from many (or all) of the burdens of child raising. This would also allow for many new and interesting options for territory and culture expansion.
Their young need to be able to fend for themselves.
For the young humans to have a chance in their new environment, they would need be able to function both physically and mentally after birth. Having stronger survival instincts (like snakes or turtles) would be very helpful.
Their young could benefit from multiple life stages.
Perhaps the new babies hatch into a worm form, and live in the soil for many years before transforming into their human form (like many insects.) They could also spend many years in a plant form, rooted to the ground while absorbing sunlight and nutrients. Either way, they would benefit from having an intermediate form which allowed them to grow and mature.
Their society would need a culture that dealt with unattended children.
Their culture would need to be able to deal with the herds of unsophisticated children running around. Perhaps they would accept this brutal stage of life as an important right of passage. Perhaps they would regard their offspring as a lower form of life until they evolve or morph onto mature humans. Either way, egg laying humans would regard human rights drastically different that we do. Keep in mind, may egg laying creatures eat their own offspring! Other creatures care for young that they did not produce. Either way, these human's laws and traditions would need to have some regard for eggs and young.
They could be telepathic or have a hive-mind.
Many of the complications of egg laying could be resolved through some form of telepathy or linked mind. If the humans shared a hive mind, then newly hatched people would emerge as an integral part of that society. Even if they were only telepathic, the newly hatched people would benefit from the experence and company of the older ones.
