The purpose of this post is to examine the history of genetic modification in the Federation, prior to "Strange New Worlds". I've tried to compile various references to genetic engineering, eugenics, cloning, and genetic resequencing within the Federation across all series, with quotes and additional context as needed. All examples are presented in real-world chronological order, to better examine how these ideas have evolved over the history of the franchise.

The first reference to eugenics I could find is in the Original Series episode, "The Conscience of the King". In that episode, they briefly described how Kodos was employing his own theories of eugenics when he enacted the massacre at Tarsus IV:

Spock: Kodos began to separate the colonists. Some would live, be rationed whatever food was left. The remainder would be immediately put to death. Apparently, he had his own theories of eugenics.

McCoy: Unfortunately, he wasn't the first.

Spock: Perhaps not. But he was certainly among the most ruthless; to decide arbitrarily who would survive and who would not, using his own personal standards, and then to implement his decision without mercy. Children watching their parents die. Whole families destroyed. Over four thousand people. They died quickly, without pain, but they died. Relief arrived, but too late to prevent the executions.

The subject comes up again, of course, in "Space Seed", when Khan and his fellow prisoners are discovered:

McCoy: The Eugenics Wars.

Spock: Of course. Your attempt to improve the race through selective breeding.

A later statement from Kirk affirms the root cause of the Eugenics Wars:

Kirk: An improved breed of human. That's what the Eugenics War was all about.

Spock is the first to suggest that there was a fatal flaw in the engineering process:

Pock: In 1993, a group of these young supermen did seize power simultaneously in over forty nations.

Kirk: Well, they were hardly supermen. They were aggressive, arrogant. They began to battle among themselves.

Spock: Because the scientists overlooked one fact. Superior ability breeds superior ambition.

Kirk: Interesting, if true. They created a group of Alexanders, Napoleons.

Khan himself has some thoughts on his own abilities relative to the rest of humanity:

Khan: Captain, although your abilities intrigue me, you are quite honestly inferior. Mentally, physically. In fact, I am surprised how little improvement there has been in human evolution. Oh, there has been technical advancement, but, how little man himself has changed.

Little is said about genetic engineering for quite some time, until we get to The Next Generation's "Unnatural Selection". This one appears to be a bit of an outlier, given what we later learn about genetic enhancement, but it may be possible to reconcile it. When the Enterprise crew first meet Dr. Kingsley of the Darwin Genetic Research Station, she makes the nature of her research seem as innocuous as possible:

Kingsley: Our research here is limited to human genetics. I can assure you we're not dealing with something that got away from us. We believe that we were infected by a supply ship that was here three days ago.

Later, she acknowledges that the children aboard the station are genetically enhanced, with an interesting caveat:

Kingsley: Our ultimate achievement. The oldest is twelve, and all are telekinetic. Watch.

Pulaski: Genetically engineered?

Kingsley: Not engineered, created. Perfect in every way. Their body structure, their musculature, their minds.

I find it very interesting that Kingsley draws this line between "engineering" and "creation" - this distinction seems to hold some relevance to her, but it's not explored in the episode itself. Could Federation law draw a distinction between genetic modification of living individuals and cloning?

This episode also gives us an example of a genetic medical treatment of sorts, when the transporters are modified to filter out the genetic changes Pulaski endured when she transported over to the Darwin station.

Another Next Generation episode, "Up the Long Ladder", reveals some attitudes about cloning, specifically:

Riker: You want to clone us?

Granger: Yes.

Riker: No way, not me.

Granger: How can you possibly be harmed?>

Riker: It's not a question of harm. One William Riker is unique, perhaps even special. But a hundred of him, a thousand of him diminishes me in ways I can't even imagine.

Notably, when Riker and Pulaski are cloned without their knowledge or consent, Riker destroys the clones outright while they are still developing.

The episode also mentions "replicative fading," a process by which errors creep into the chromosomes of clones across successive generations, until the clones are no longer viable.

In Deep Space Nine's "A Man Alone", Odo arrests Ibudan for murdering his own clone in an attempt to frame Odo for murder:

Odo: Killing your own clone is still murder.

Notably, Odo is likely referring to Bajoran law, not Federation law, in this case.

The Next Generation's "Bloodlines" contains an early reference to DNA resequencing, a term which will be used more frequently going forward. It is also another example of flawed genetic manipulation:

Picard: You know as well as I do, Bok, he's not my son. I know what you've done. Miranda Vigo is his mother but I am not his father. You made it appear so because you resequenced his DNA. But your technique was flawed. He developed a neurological disorder. When my ship's Doctor investigated it, she discovered what you had done.

Later, Jason Vigo notes that he is responding well to an unspecified treatment provided by Doctor Crusher, and that the damage caused by the DNA resequencing may be completely reversed.

Federation law regarding genetic enhancements starts to come into focus in Deep Space Nine's "Doctor Bashir, I Presume":

O'Brien: You're not a fraud. I don't care what enhancements your parents may have had done. Genetic recoding can't give you ambition, or a personality, or compassion or any of the things that make a person truly human.

Bashir: Starfleet Medical won't see it that way. DNA resequencing for any reason other than repairing serious birth defects is illegal. Any genetically enhanced human being is barred from serving in Starfleet or practising medicine.

Later, Rear Admiral Bennett makes the case for these laws, echoing the sentiments of Spock in "Space Seed":

Bennett: Two hundred years ago we tried to improve the species through DNA resequencing, and what did we get for our trouble? The Eugenics Wars. For every Julian Bashir that can be created, there's a Khan Singh waiting in the wings. A superhuman whose ambition and thirst for power have been enhanced along with his intellect. The law against genetic engineering provides a firewall against such men and it's my job to keep that firewall intact.

It's interesting that ambition is something specifically cited by O'Brien that cannot be influenced by genetic resequencing, while Bennett says that it can.

In Voyager's "The Raven", the EMH uses genetic resequencing to neutralize Seven of Nine's nanoprobes. Borg nanoprobes are obviously not a birth defect, so it appears that other medical uses of resequencing are considered ethical and legal.

Continued in the comments...