The Star Trek character Spock is one of the best-known and beloved characters in American television. He is a central character in season two of Star Trek Discovery, and he began the story arc more...emotional than we might have expected.
How has Spock's character evolved over the years, spanning multiple series?
We first see Spock as the son of a Vulcan man and a human woman. In The Animated Series, a seven-year-old Spock is bullied by other Vulcan children for being part human. He struggles with his emotions, particularly when his (very large) pet shelat, I Chaya, is critically wounded in the wilderness. Spock chooses to allow an animal healer to provide I Chaya a painless death, rather than living on in pain. In doing this, Spock chooses to live his life in the Vulcan way of logic.
But in Discovery, we learn that Spock at a similar age also had affection for his older, human foster sister, Michael Burnham. Their father, Sarek, had hoped that Michael would help Spock learn to balance the two sides of his personality, the more logical Vulcan alongside the more emotional human side.
But Michael unwisely drove Spock away, out of fear that "logic extremists" who were vexed that mixed-bloods were among them on Vulcan, would target Spock rather than herself. This rift, according to Spock in Discovery, caused him to pursue logic more ardently, but immediately after his youthful confrontation with Michael, Spock experienced a vision from the "Red Angel" telling him how to find the endangered Michael.
Thus we have competing influences in the young Spock that affect his balance between logic and emotion. Fans generally accept the animated episode as "canon" for how Spock came to embrace the logical side of his makeup. But the version of Spock who comes from the Discovery writers gives us a Spock who continues to be unbalanced between logic and emotion (as well as possessing a never-before-mentioned learning disability, which must have complicated his young life).
Sarek eventually arranges for Spock to join something the Discovery writers called the Vulcan Expeditionary Group, but Spock joins Starfleet instead. It has long been part of Trek continuity that Sarek actually wanted Spock to join the Vulcan Science Academy, and refused to speak to Spock for 18 years when Spock choose Starfleet. Discovery implies that Spock did not actually attend Starfleet Academy, but joined in some other way. This is supported by Spock's statement in The Wrath of Khan that he had never taken the Kobyashi Maru test. Michael also did not attend the academy and made her way to a Starfleet commission via an alternative route.
We next see Spock as a lieutenant on the Enterprise a dozen years before Kirk takes command and a couple of years before he appears in Star Trek Discovery, which is set a couple of years AFTER the original series pilot. That pilot episode, The Cage, was the first time Leonard Nimoy played Spock and the character was not yet fully formed, but this Spock grins, often raises his voice, and generally behaves more emotionally that we expect today from a Vulcan character.
In Star Trek Discovery, Spock also begins his the season in a more emotional frame of mind, expressing anger, which Captain Pike, who had known him for some time, finds to be uncharacteristic. Specifically, something triggers nightmares about the red signals, and Spock goes so far as to check himself into a psychiatric facility at Starbase 5. The writers were never explicit about what triggered this, but the implication is that Michael's mother, using The Suit, somehow triggered it, because it was needed for the overall defeat of Control.
By the Original Series, Spock had become generally logical and unemotional, but with strong friendships aboard Enterprise, presumably prompted by Michael Burnham's farewell admonitions to find people who seem farthest from him and to let them guide him to balance. This is generally considered to be a foreshadowing of Spock's relationship with Kirk, but it also heralds his sparring friendship with McCoy.
In TOS, however, viewers had repeated hints that, when Spock was under stress, drugged, etc., his emotions were just below the surface. As we have seen, this is true of all Vulcans. They are not automatically logical. They learn to actively suppress emotions.
Indeed, in The Motion Picture, shortly after the end of the Enterprise five-year mission, Spock undergoes the Kohlinar ritual to purge the last vestiges of emotion, suggesting that he wanted to end his balancing act between logic and emotion. This would have been almost exactly 15 years after the Discovery season finale.
Maybe no longer being shipmates with Kirk, McCoy et al. meant Spock lost the balance they provided, although one would have hoped that the 15-year older Spock would have learned more self-regulation in the intervening years.
Regardless, Spock does not complete the Kohlinar, because Vger mentally calls to him across space, and an emotion, curiosity, gets the better of him. I can imagine Spock thinking, "Again?" Was he secretly saying "this could be Control, I've got to return to Enterprise to check it out."
In the Motion Picture, Spock mind melds with the pure logic of Vger and finds it to be lacking. He comes to the realization that both parts of his personality, logic and emotion, must synergize. Possibly for the first time, he becomes fully comfortable with who he is and his ability to balance logic and emotion.
Of course, a few years later, he dies, has his katra refused with his body, and has to go through the process of discovering balance all over again.
Later in life, Spock becomes an unofficial ambassador to the Romulans. Because the Romulans were so driven by emotion, reuniting them would have meant the same epiphany for the cultures as Spock earlier had for his own personality. So he becomes a teacher, living in hiding, until possibly after the events of Star Trek Nemesis.
In the Kelvan timeline, weird things happen. Spock goes back in time and eventually dies. In the main timeline, we do not (yet) know Spock's ultimate fate (the movie rights and the TV rights are held by different companies and they are not obligated to conform to each other, however TV executive producer Alex Kurtzman has been involved in both).
From a storytelling point of view, episode and movie writers have enjoyed placing the logical and unemotional Spock in circumstances that disconcerted him and allowed his emotions to bubble out. From an in-universe perspective, however, we can see that Spock has ebbed and flowed back and forth, between more and less emotional orientations, more and less balance.
Of course, the season finale of Discovery provides a rationale for why Spock has never mentioned Michael, even to his closest friends. Spock is good t keeping secrets - remember that he also had an older half-brother, Sybok, who he did not mention for decades.
At the conclusion id Discovery season 2, Spock's character is ready for the mindset we see in the Original Series and beyond. If by chance a Captain Pike series happens, I hope Spock is fully recognizable as his in-balance TOS self.
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