Could human beings evolve to have longer gestation periods? If so, how could this be done?

Question

Hopefully, this is a little less broad. Apologies if it isn't! I'm rather new here, so I'm not used to this yet. Oops. Also, apologies for the length - I'm trying to explain as much as I can.

To pull some of the stuff I know already; Human babies are born underdeveloped compared with other primates. Our brains are less than 30 percent their adult size at birth, compared with around 40 percent for chimpanzees, our closest living ape relative. It would take a gestation length of 18 to 21 months instead of nine months for human babies' brains to reach that level of development.

I'm not entirely sure why humans cut off so soon, past something to do with their pelvis and standing upright. The species I'm developing, however, needs to be more active from the get go - not that I'm saying they need to give birth to teenaged kids or anything, just that here are more areas in the brain that need to develop. I'm aware the kids are likelier to be bigger as a result when they are born, considering they need extra time to develop.

If a species changes, usually, it needs a reason to change. In the case of my species, the brain needs to develop further for the child's survival. This has to do partly to account for some changes from the 'human' setting. If, uh, that makes sense. I'm kind of using humans as a base here. (Evolved parallel to, branched off at one stage.)

The brain, for one, needs to possibly account for any changes as a result of heightened senses, hearing and smell in particular. This particular one is brought on due to the fact that the planet is rather cluttered - this has bred a large amount of species who rely on stealthier tactics. Though the world is varied, I picture something perhaps mountainous and/or heavily forested for the general area this species evolved in. (Leaning more towards 'rainforest' as opposed to plain 'ol forest.) They've spread out pretty recently - but they've still adapted to this particular environment.

Another change is magic; like I brought up in an earlier question that I worded a bit awfully, it highly impacts this species (and many others native to the planet), to the point where it has interwoven into their evolutionary process. It's second nature to them, like how humans have evolved for... hunting? Help, words. Take the wizards from Harry Potter as an example. One needs to be born with the magical ability to actually go around wielding magic. Wizards can, but muggles (normal humans) cannot. Occasionally people are born who can't use his magic, regardless of bloodline (squibs). The failure to develop this magical ability for my race, as a result could be due to premature birth or birth defects.

I'm aiming for the gestation period to last as long as 15 to 21 months, if required - it's likely I'll be adding or adjusting other areas of brain development later. I can handwave some of it, but not everything. The race was more solidary many millions of years ago, but over time developed into something resembling larger flocks. This is only strengthened further once longer gestation periods become a thing, considering the one carrying the baby isn't going to be at her peak if/when predators come.

The senses and inclination to magic are what I'd consider defense mechanisms. Natural ways the body has evolved to let them survive. Kind of like long necks on giraffes, though my race doesn't go around hitting people with their necks... well, not yet, anyway.

I'm planning to keep the race bipedal, if possible, or perhaps being in some process of evolving away from the whole four legged thing. Vaguely humanoid. The organs and stuff on the other hand are basically free range if it gets the desired results though.

I'm not really sure what else to add, but I'll keep an eye out so I can edit accordingly. Sorry for the brain-vomit and I appreciate any help.

Answer 1

Magic

Considering the magic ability isn't something that has a strong basis in most science, you should have some reasonable leeway with your pseudo-human biology, so long as it remains logical and remains in theme with the rest of the magical abilities.

Let's go over the basics of your setting, which I will be using as the basis for this response.

The pseudo-humans have developed more acute senses of hearing and smell, driven by the more dangerous and shady environment. How this is manifested, however, is not clear. Do they have larger ears and better noses? Perhaps changes in their brain allow for better processing of the information? It's unclear, but I will address my solution in a moment.

Next, there is magic that was developed as a defense mechanism, but it isn't mentioned what kind of magic or what it is capable of. I'm going to take some liberties with it, but I assume it can be used to enhance the sense of the pseudo-humans.

Lastly, these pseudo-humans need to have a longer incubation, with the purpose of having a better initial brain-state when they are born.

My logic is that the embryo is capable of very basic versions of magic, and probably only the most common and useful application for your species, magic pertaining to sensory improvement.

While in development, the embryos will develop their magical abilities (to a small extent) in preparation for their birth. As early as 20 weeks, human embryo's have developed ears that can hear. Pseudo-human embryo's will be able to amplify their hearing to be able to gather more understanding and learning of the outside environment. During this time, they remain in gestation, developing more while learning from a controlled and contained environment. This provides time for their brains to develop with minimal downsides to their prolonged stay.

In comparison, embryo's with defects that are unable to perform magic are born after 9 months, similar to normal humans, since they have no need to remain and develop their abilities.

This provides an easy and quick ways to tell if a child will be magical or not. There could be celebrations around the 10 month mark to celebrate the assumed abilities of the child. Their will need to be small modifications to the child-bearing pseudo-humans for them to be able to support larger babies (like the wider hips, and possibly just larger in general since it's more weight for much longer to carry), but evolving to be larger based upon an environment isn't unrealistic, nor does it require much explanation to be accepted.

Answer 2

Physiology

This may seem overly simplistic, but you could easily have a longer gestation period in humans if the mother had bigger hips.

Generally, if it's a matter of life and death for the infant to be further along when born, it will be. In modern society, we heavily coddle and care for our young, so walking isn't a matter of life and death (unlike many herbivorous quadrupeds which can walk almost immediately at birth because it is life or death if they don't). You might also consider the mother: the larger the baby, the more difficulty they will have in caring for themselves.

I could see this developing in a society where the baby is almost immediately put into more harsh circumstances where it must be more proficient to survive, but the mother is very well protected for most of the gestation period.

Answer 3

What would you like the babies to be able to DO when born or in hours or months? Please edit your answer and list them. Your question post includes a lot of info, but in order to answer it, a list of the features you want and WHEN you want the baby to have them. Things like walking, senses...lay it out

• Perhaps as bullet points

I will edit my answer accordingly, to solve the problem of a more developed baby, whatever that might mean.

In the meantime, let me say that longer gestation is likely not going to solve this problem.

Here's an article that covers why helpless babes were naturally selected. Note that the pelvis thing, which is present in older research, may not actually be the reason.

to accommodate an infant at a chimplike stage of brain development—that is, a brain that is 40 percent of adult brain size, or 640 cubic centimeters—the pelvic inlet (the top of the birth canal, which is the narrowest part) would only have to expand by three centimeters on average. Some women today have pelvic inlets that wide, and those larger dimensions have no measurable effect on locomotor cost. ...

That other factor, they contend, is mom’s metabolic rate. “Gestation places a heavy metabolic burden (measured in calories consumed) on the mother,” Dunsworth and her co-authors explain. Data from a wide range of mammals suggest that there is a limit to how large and energetically expensive a fetus can grow before it has to check out of the womb. Once outside of the womb, the baby’s growth slows down to a more sustainable rate for the mother. Building on an idea previously put forth by study co-author Peter T. Ellison of Harvard University known as the metabolic crossover hypothesis, the team proposes that “energetic constraints of both mother and fetus are the primary determinants of gestation length and fetal growth in humans and across mammals.” By nine months or so, the metabolic demands of a human fetus threaten to exceed the mother’s ability to meet both the baby’s energy requirements and her own, so she delivers the baby. ...

Rosenberg additionally noted—and I found this especially fascinating—that the authors mention the possibility that the timing of birth actually optimizes cognitive and motor neuronal development. That idea, first proposed by Swiss zoologist Adolf Portman in the 1960s, is worth pursuing, she says. “Maybe human newborns are adapted to soaking up all this cultural stuff and maybe being born earlier lets you do this,” she muses. “Maybe being born earlier is better if you’re a cultural animal.” Food for thought.

We are as probably as smart as we are BECAUSE most of the development is not done inside the womb. Our interactions with the world as we develop are the reason why we are intelligent. We are the most intelligent animal on the planet and we give birth to some of the most helpless babies...there may be a reason why we are unique in this way. It's an advantage. Chimps might be more developed when they come out, but they also have less capacity for intelligence over a life time.

It's not a plus to intelligence if the brain just develops inside the womb. Consider this article on the difference between a great ape and ourselves. A mutation in the jaw muscle allowed us to continue to develop after birth, which is an ADVANTAGE, not a disadvantage.

The species that are nearly fully formed and developed (like horses for instance) tend to be not so bright.

Answer 4

It is not at all clear to me what would be the advantage with a longer gestation period, but assuming there is a valid reason (and that no one would actually attempt what I am about to suggest - a risky assumption I'm sure), here goes: By killing all infants born early or on time, it seems possible that the human gestation period would increase as a consequence of artificial selection.

It would probably be necessary to set the initial target to be not too much larger than the current average and only gradually raising it over the long experiment. Otherwise there is of course the risk of catastrophically diminishing the human population.

A few centuries, not to mention perhaps billions of dead babies, later - viola - a longer human gestation. Of course certain practical and ethical difficulties present themselves.