With crystal-clear scans of unborn babies now before them, a group of scientists can’t quite believe their eyes. It seems that they’ve made a shocking observation, one which could have profound scientific implications. It’s a little early to say for certain, of course, but this work might just rewrite our understanding of human evolution.
In order to conduct this research, the scientists made use of novel and sophisticated technologies. With them, they were able to produce some extremely detailed scans of developing babies inside the womb. These images, it appeared, were exhibiting an unusual feature of fetuses which had never previously been noted.
The ramifications of this find could prove to be momentous. As we’ve mentioned, the work may contribute to a new and more accurate comprehension of how human beings have evolved. And perhaps even more importantly, it could offer experts a greater insight into certain defects with which babies can be born.
Of course, the scientific community has long sought to detail the progress of unborn human babies. Indeed, the commonly-used terminology for this process is “prenatal development.” In most cases, this occurs for roughly 38 weeks across three different phases. First, we have the germinal stage. This is followed by the embryonic phase, which leads finally to the fetal stage.
Before any of these stages can get under way, of course, conception must take place. This can only happen after a woman’s egg has been transported from her ovary into one of her fallopian tubes. This transpires every month and is known as ovulation. A woman has a pair of fallopian tubes, each one of which is connected to the womb.
A woman’s egg can only be fertilized when a male’s sperm has found its way into the fallopian tubes. This can happen after sexual intercourse or, indeed, after an artificial insemination method has taken place. It may take many hours for the sperm to make its way into the tubes.
Once there, the sperm has an opportunity to pierce the outer layer of the egg. If this happens, the two fuse together and a singular cell known as a zygote is brought into being. From here, then, the initial germinal phase of a human baby’s development can start to unfold.
At the outset, a process referred to as cleavage takes place, wherein the zygote starts dividing at a swift rate. It initially splits into a pair of indistinguishable cells, which themselves become four cells, then eight cells, then 16, and so on. All the while, these cells have been traveling through the fallopian tube towards the womb.
At 16 cells, this new entity can be referred to as a morula. This eventually reaches the end of the fallopian tube and arrives at the womb. Here, the cells continue to divide, with a sort of pocket known as a blastocoele developing in the middle of them. The morula turns into something called a blastocyst, which is now made up of between 200 and 300 cells.
Next, generally some six days since conception took place, the blastocyst plants itself into the wall of the womb. Owing to hormonal reactions, it then works through this wall and into the womb’s tissue. This is a step known as implantation, and it represents the final part of the germinal stage of development.
What follows next is the embryonic stage, and this second phase runs up to roughly week eight of the pregnancy. As with the previous germinal stage, this second chapter sees the cells persisting in their swift divisions. However, collective groups of these cells start to assume unique properties: this process is known as differentiation.
At the point of differentiation, something called gastrulation occurs. This is when the blastula becomes a more complex entity referred to as the gastrula. This is made up of three different “germ layers;” one which forms at the exterior, one in the center and one between them. These layers are the ectoderm, the endoderm and the mesoderm respectively. Each one develops into something distinct from the other two.
The outlying ectoderm, for instance, will eventually develop into a baby’s skin, brain, mouth, various tissues and much more besides. The middle mesoderm, by way of contrast, becomes things such as muscle, bone, the lungs and the reproductive organs. Finally, the endoderm turns into things including the tongue, parts of the digestive system and the lining of several organs.
Differentiation is something which occurs for several weeks, with numerous body parts coming into being at the same time. During its earliest stages, in about the third week of pregnancy, important things begin to form in an embryo. Indeed, the beginnings of the heart, brain, digestive system and spinal cord can be observed during this period.
By the following week, the growth of bones should be under way. In fact, little buds representing the beginnings of the limbs will be present. The face will start to be composed, and the brain and heart will continue to progress. The heart, in fact, should actually start pumping about this time.
By the fifth week, the eyes, lungs, nose and kidneys should be showing signs of coming into being. Next come the feet, hands and their respective toes and fingers. During week seven, we should be seeing things like the eyelids, hair follicles and sexual organs starting to form. Flickers of brain activity will start from here.
The eighth week marks the close of the embryonic stage. By this time, the embryo will have formed its most vital structures and the brain can bring about muscle movement. From here on out, the embryo is designated as a fetus. Naturally, this is the start of the fetal stage of prenatal development. It’s during this final phase that the most striking progress is made.
At the earliest point of this final phase, a fetus tends to measure up at just over 1 inch long. Furthermore, it weighs roughly just a tenth of an ounce. However, after 30 or so more weeks, it should be about 20 inches long and weighing close to 7 pounds.
During the first few weeks of the fetal stage, however, the fetus should be a little over 3 inches. Its head should comprise about half its overall magnitude, with facial characteristics and hands and feet becoming more defined. Now, in fact, is the time in which the fetus should be capable of forming a fist.
By about the 15th week of the pregnancy, the fetus may be somewhere close to 6 inches long. Delicate hairs known as lanugo begin to sprout on its head, all as organs, bones and muscles continuously grow. At this point, the fetus will be capable of performing swallowing and sucking actions.
Next, the soft lanugo starts to spread across all the skin, under which fat begins to cultivate. The fetus might now be able to move to such an extent that its mother can feel it. Then, by week 24, its head hair should be more lengthy, and its lungs and eyes should be more advanced.
Between the 25th and 28th weeks of the pregnancy, the progress of the brain and nervous system will advance greatly. The fetus will be able to open and shut its eyes, and it’ll generally have more command of its own behavior. The lungs will now be capable of taking in air.
Over the next few weeks, fat should be more prominent beneath the fetus’s skin. Its bones will be very soft, but they’ll be clearly defined. The lanugo will withdraw from the skin, and the fingernails will now be entirely present. By week 36 the fetus will usually measure from 15 to 17 inches in length.
Now, in the final two weeks of pregnancy, the fetus should be ready for birth. Its lanugo will be almost entirely gone, with harder head hair now in its place. If everything is as it should be, all the organs should be healthy and working. A baby will soon be born.
Of course, there are many factors which can prevent the healthy development and birth of a baby. Indeed, abnormalities might occur at some point, ultimately resulting in a variety of complications. Some of these can be rather insignificant, while others can be so serious as to lead to death.
It should go without saying that prenatal development is an extremely important process. As such, it has often been the subject of scientific inquiry. After all, the more we know about how fetuses develop, the more we can ultimately learn about human beings, our features and the functions associated with them.
As with every other species on Earth, human evolution hasn’t been a smooth or target-oriented process. This can be evidenced in the fact that several parts of our body no longer have any purpose whatsoever. Wisdom teeth, for example, once aided ancient humans in chewing up plants: now they just bother us when they come through.
In recent times, though, some scientists noticed something more subtle which is seemingly indicative of the human evolutionary process. On October 1, 2019, these researchers published their study in the aptly named Development journal. In it, they suggested that developing babies actually possess hand muscles resembling those of lizards.
After about seven weeks, the researchers behind the study noticed a fetus that had 30 muscles in its hands and feet. But five weeks further on, roughly ten of these muscles had either disappeared or combined with one another. Two of these muscles taken together can be termed as dorsometacarpales.
Muscles such as these can actually be found in several creatures alive today, perhaps most notably in lizards. In the case of humans, however, it’s been suggested that they ceased to exist in adults some 250 million years into the past. The fact that we see them in fetuses, then, represents something of a snapshot of the course of human evolution.
Specifically, the muscles appear to be leftovers from the broad period in which reptiles started to evolve into mammals. And while the precise reason that they’re present during prenatal development before disappearing isn’t clear to date, it’s been posited that over time they became unnecessary for our survival. Yet our thumbs do actually retain an additional muscle making them more adroit than our fingers.
The researcher who led the study is Dr. Rui Diogo, who is associated with Washington D.C.’s Howard University. Speaking to British broadcaster the B.B.C. in 2019, Diogo elaborated on the additional thumb muscle. “We have a lot of muscles going to the thumb, very precise thumb movements, but we lost a lot of muscles that are going to the other digits,” he said. “In our evolution, we do not need them so much.”
Dr. Diogo went on by pondering why the thumb had retained its muscle while the other fingers had not. He said, “Probably, we cannot just say in evolution, ‘Look, I will delete from scratch, from day zero, the muscle going to digits two, three, four, five and I will just keep the one going to the thumb.’ Probably it is not so easy. Probably you have to form this layer of this muscle and then it disappears on the other digits but persists on the thumbs.”
Apparently, scientists have actually recorded some people as having a number of the dorsometacarpales that typically disappear in the womb. However, it’s never the same number of the muscles that can be seen in embryos and fetuses. In the cases where the muscles do last in people after birth, they can be connected to abnormalities in the person’s limbs.
According to Dr. Diogo, the muscles are a particularly compelling illustration of evolutionary processes in humans. Even more so, he has claimed, than things like our wisdom teeth, our appendix or our tailbones. As he proclaimed to the BBC, “No adult mammal, no rat, no dog has those muscles. It’s impressive. It was really a long time ago [that we lost them].”
The B.B.C. also spoke with Dr. Sergio Almécija, an ape and human evolution expert from the American Museum of Natural History. Dr. Almécija claimed that this study could be important, but that it ultimately posed several questions. He said, “The novelty of this study is that it allows us to visualize – with precision – when exactly during our development some structures appear and/or disappear.”
Dr. Almécija continued, “The important question for me now is, what else are we missing? What will we find when all the human body is inspected at this detail during its development? What is causing certain structure[s] to …[appear and] disappear? We can now see how it happens, but what about the why?”
Scientists have also taken a look at the feet of unborn babies to look for something similar. As it turns out, here, too, muscles can be noted which later vanish. Such feet muscles can actually be seen in other primates, who use their feet for climbing and other tasks in ways that we do not.
Dr. Diogo has reflected that losing these muscles in our hands and feet isn’t necessarily to our advantage. “Some of the things we are losing, it’s not that we are getting better humans and more progress. No. We are really losing things that will make super-humans. Super-humans would be keeping those muscles because you would be able to move all your digits, including your feet, as thumbs. We lost them because we do not need them.”
The research conducted by Dr. Diogo and his colleagues is fascinating, but ultimately more studies will be required. Thankfully, such works appear to be in the pipeline. And as the scientist himself told the B.B.C., “It used to be that we had more understanding of the early development of fishes, frogs, chicken and mice than in our own species. But these new techniques allow us to see human development in much greater detail.”