The Source: Morphology, Evolution, Transmission, and Death
This is a study on the morphology of the Source and its evolution, leading to the following key theories in regards to its transmission and death:
Since speciation, the Source has been residing within the FT (i.e. it has never died, which is why the Power of the Titans still exists), and it can only move from host to host via oral consumption.
The Dinosaur Titan is the Source itself, so destroying this Titan form is the key to nullifying the Power of the Titans once and for all.
In this analysis, speciation refers to the event in which the Source merged with Ymir’s spine to create a new and distinct species; that is, the Subjects of Ymir.
Disclaimer: This is purely a theory based on my own observations and inferences.
The Morphology of the Source and Its Evolution
Chapter 137
Based on its original form, the Source is composed of five main parts:
the head (x1), denoted by the yellow circle and distinguished as the more bulbous end
the spine (x1), denoted by the magenta line
the tail (x1), denoted by the red circle
the limbs (x9 on each side, with each end splitting into two), denoted by the blue circle
the spikes (x8 on each side), denoted by the green oval
While the Source retains this general form throughout the years, some of the parts show evidence of evolution over time:
Prior to speciation
The tail develops an antenna (much like the split ends that accompany the limbs).
The spikes lose their rigid structure (although this may be a matter of the Source exercising different methods of locomotion, such as swimming vs. terrestrial).
There are 13 spikes on each side of the spine.
Chapter 122
After speciation
The tail undergoes further splitting, forming tentacles.
The length of the spine increases, causing the number of limbs and spikes to also multiply (there are more than 9 and 13 on each side, respectively).
However, it’s important to note that these changes might have only been instigated due to the formation of the Dinosaur Titan.
Chapter 137
Chapter 137
Speciation and the Morphology of the Subjects of Ymir
This section examines how each of the five morphological features making up the Source combined with Ymir’s spine during speciation to give birth to SoY.
Chapter 137
The spikes attached themselves to Ymir’s spinal cord.
The length of the Source settled along Ymir’s spine.
The head and the tail fused themselves with each end of Ymir’s spine. Interestingly, the head is actually the part that bonded with Ymir’s sacrum (creating what I believe to be the compartment where titanizing spinal fluid is stored), while the tail settled in her upper cervical vertebrae (thereby providing the connection between the Source and the human brain). Essentially, the Source merged to parallel an upside-down human spine.
The limbs wrapped themselves around Ymir’s ribcage, reinforcing her ribs.
Chapter 122
In this way, the Source and Ymir entered a symbiotic relationship, one of both parasitism and mutualism. Additionally, the Source altered Ymir’s intermediate anatomy such that all SoY are only morphologically distinct from other Homo sapiens through the construct of their spines.
Bonus: Speciation and the Neurology of the Subjects of Ymir
If we consider the head of the Source to be where its coordination centre resides, it can be argued that the body of a SoY houses two brains along both ends of their spine.
This is why, even if the human brain of a shifter sustains damage (e.g. Reiner) or the connection between the Source and the FT’s human brain is severed (e.g. Eren), the SoY is still able to heal.
In Reiner’s case, since the source brain in the hybrid spine within him was still functioning, it allowed for the transfer of his consciousness while his human brain regenerated. As for Eren, he was rescued from death because the brain of the Source residing within him commanded the tail to reattach itself to his human head (more on this later).
The Transmission of the Source via the Founding Titan
Now, since the Source merged with Ymir’s spine to create this fused spinal structure, it’s important to keep in mind that her spine and the Source are one in the same. Consequently, although Ymir passed on the morphological features of her hybrid spine to her daughters (and subsequent SoY) by means of hereditary genetics, they weren’t born with the original Source inside of them (because there is only one of it and it was bound to her spine). It’s not until they ate her that the Source migrated to one of their bodies, and that would be whoever inherited the FT (which I suspect is the first person to have consumed a part of her spine).
In other words, the FT wielder is the only SoY whose spine houses the Source (+ the spine of Ymir, which is what’s been allowing her to live on). This is essentially what distinguishes the Coordinate from the rest of the Nine Titans.
Secondly, for the FT to be inherited, the Source needs to physically move from one host to another. This is accomplished via oral consumption. Once consumed, the Source is able to use its healing power/ability to grow in size (which it lends to SoY through the Power of the Titans) to grow back inside the new FT wielder and bind with their spine. Thus, much like other real-life parasites, being consumed is not fatal to the Source.
The Weaknesses of the Source and its Singular Cause of Death
While the Source can surpass death by cycling through a multitude of hosts, it can be inferred that it can only do so by (1) being physically transmitted, and (2) maintaining a physical connection with a live host. That is to say, these two requirements are the weaknesses of the Source and the key to its fatality.
To elaborate, the physical transmission requirement would mean that the Source (and therefore the FT) cannot actually be passed along to a newborn baby via PATHS. I believe that ability is only inherent to the other Nine Titans since their shifters do not house the Source within their bodies. Consequently, if the FT wielder were to die without having their spine consumed, that would spell the end of the Source.
This leads me to an explanation for the Source’s behaviour in chapters 122 and 137. Since the goal of the Source is to persevere in life, if its connection to its host is severed (and no transmission follows), it will always automatically revive the FT wielder using its healing ability, even if they’ve been beheaded. In other words, the FT cannot actually be killed by traditional means of severing the nape, because the Source will instinctually heal/revive its host if its weaknesses are exploited.
Chapter 137
Thus, in order to kill the Source and destroy the Power of the Titans once and for all, one must kill its host (the FT wielder) and prevent its failsafe mechanism (the revival of the shifter) from succeeding.
The Transformation of the Source into the Dinosaur Titan
Having established that the Source, Ymir’s spine, and the FT are one in the same, as the current FT wielder, Eren’s spine is also a part of this entity. This is why, when Eren’s spine leaps out of his body to reconnect with his head at the end of chapter 122, it looks more like the Source than it does a regular human spine. Essentially, activation of the failsafe mechanism causes the Source to revert back to its original form (this is also why, when Jean later blasts the Dinosaur Titan’s head off, the Source spews out of its spinal cord in its original form).
Chapter 122
Thus, the Dinosaur Titan that subsequently forms is a manifestation of the Source itself. This is also evident in the way that its upper half (denoted by the black circle) exhibits the morphology of humans while its lower half parallels the original form of the Source.
Chapter 130
To further illustrate, the following morphological features of the original Source correspond with the following parts of the Dinosaur Titan’s upper half (the human skeleton):
the tail = the skull (with the tentacles serving as the connection between Eren’s human head and the spinal cord of the Dinosaur Titan)
the spine = the spinal cord
the limbs = the ribcage
the spikes = the vertebrae
Chapter 122
As for the Dinosaur Titan’s lower half, it fully parallels the original form of the Source but on a larger scale. It also excludes the tail as that part belongs to the upper half of the structure.
Implications for the Ending
Putting all of this together, what’s important about the Dinosaur Titan being the Source itself is that, if the Alliance manages to destroy it before it can reconnect with Eren’s human head, then that should result in its death (as well as Eren/Ymir’s) and consequently, the end of the Power of the Titans.
And while the key to destroying the Power of the Titans might seem too simple, keep in mind that it has never been possible because the Source does its best to keep its host alive. There is also the fact that the FT was passed down the royal family through traditional means before Grisha came along.










