Because he looked at the drawings in the records. It recorded that Baratheons fathered dark-haired children, regardless of the color of the mother’s hair. And presumably he also saw that Lannisters didn’t always beget blond-haired children.
The question is why does the exact detail here matter.
We know very well that people have always drawn conclusions or found patterns in ways that don’t stand up to modern scientific knowledge. Hell, people do it to this very day.
We also know that this is a world in which magic and the supernatural exists.
We also know that Ned—and probably everyone else in his world—doesn’t have a complete understanding of either the science or the magic of their world to answer the question.
So who exactly is going to answer this question for you? And what difference would it make if you did know the answer?
They understand it to mean that Baratheons father only dark-haired children.
We have know reason to believe that they either know nor understand anything beyond that. And if they know nor understand nothing beyond that, then that’s all that that the story owes us the audience.
And as our understanding of genetics increases we’ve learned that a lot of things we thought we knew regarding Mendelian Genetics were not entirely accurate. The factors that determine hair color are a bit more complex than the Punnett squares we learned in high school. A lot of people used to think that brown hair is dominant and blonde hair is recessive so two blonde parents couldn’t produce a brunette, but that’s incorrect. Two blonde parents can produce a child with brown hair. In a similar vein, two blue eyed parents can also produce a child with brown eyes.
So I’m willing to cut Ned some slack for not completely understanding how inherited traits work. Besides, as other people have pointed out, the hair color wasn’t the only factor that aroused Ned’s suspicions. Ned was able to guess that Jaime was the father, so he must have thought something was fishy between them. Otherwise why would Ned immediately assume that Cersei was nailing her brother and not some other blonde dude?
The GOT characters appear to be human beings very much like us, but we don’t know that genetics on their world work the same as ours (assuming it is not Earth looong ago or a looong time from now). It could be that Baratheon genes, if there even are such things, are especially dominant in a way unknown to us.
Yeah, what’s the deal with that winter that’s always coming? Why doesn’t it happen every year? Why is it longer some times than others?
This isn’t Earth, so Earth science only applies insofar as make the setting familiar and relatable. But plenty of things in the world, yes, invented to drive certain plot points, are fantastical or not completely square with our own world. Such is fiction, and the fantasy genre in particular.
I thought that the Mad King wanted Jaime in the Kingsguard to stick it to Tywin, who was the hand of the king. That way Tywin does not have an heir besides the imp and can’t complain because joining the kings guard is an honor.
I have noticed that everytime a ruler is presented with a choice between executing a criminal and pardoning them they choose execution and it goes poorly for them. Rob, Joffrey, Drago, Tywin, and Dany have all done this and it always leads to death. I hope Dany has learned from this and spares Jorah.
Jon Snow’s mother would likely be senile? Is it common for guys in their late teens or early 20s to have senile mothers? And I’d say Ned was in his 40s when he died. So he fathered a child with a much older woman?
I’m starting to believe the end of the show will be the surviving characters and dragons facing down a army of millions of zombies and white walkers and…cut to black. The end.
I just don’t see how they have time left in two more seasons to do a proper “zombie apocalypse in a fantasy setting”.
But you didn’t stop there. You said that you wanted or preferred a “consistent” scientific explanation for what’s happening. That’s exactly what I think Martin should not give us. This is not a society that understands genetics in its own world. It makes no sense for the story give us that information. We should live in the same fog of pseudo-scientific knowledge that the characters do.
There are several ways this show could go. The zombie/White Walker apocalypse is one. Another possibility is a dragon apocalypse as Dany’s dragons rain terror on Westeros. There’s the ever-present danger of winter but that seems less dramatic.
Perhaps the dragons go up against the White Walkers? And will Sam’s discovery of dragonglass/obsidian ever figure into the story?
Ned’s research didn’t find absolute proof that Cersei’s kids weren’t fathered by Robert. It was enough (for the story) for it to make Ned suspicious. Nobody need know anything about genetics, magical or otherwise, for a person to become suspicious. Ned was not shown to have absolute proof, just well-founded suspicions.
Tommen should have taken up his guards offer to clear out the fanatics, as ugly as the deaths would have been Tommen basically just lost any authority or legitimacy he had as king and this is probably the start of coup attempts.
Immediately after he backs down you can hear the crowd jeering and insulting him as a child of incest.
A king who lets some fanatics order him around isn’t going to be king for long.
No I didn’t. You will note that you are the one repeatedly using the word “science”. That’s not what I meant by saying I’d prefer if it was explained better.
So we know that a dark-haired person fathering a blonde child is no problem in Westeros, or already people would know. Ned sees a line of male ancestors with dark hair and that’s enough to give him reasonable confidence that Joffrey is not Robert’s.
Since it’s not really clear why that’s the case we can have lingering questions such as whether the book is itself incriminating…will whoever sees it know the truth, or was it just some hunch Ned made?
Finally, of course we the viewer know lots of things the characters do not, and if we were reading the novels we’d know much more than that. There is no rule of fiction that we can only know what the characters know.