It was not hard to research the Potter family tree. Indeed, though Harry was not quite five, Severus knew there were already multiple books published about the boy and his family. So he downed some Polyjuice potion and set off to Flourish and Blotts to peruse the selection. The most fatuous of the lot, Boy Who Lived: Heir of Death speculated his survival may be attributable to some mystical inheritance of his Potter blood - the author traced the family tree with gusto and concluded without any evidence whatsoever that surviving the killing curse must be a Peverell trait. He purchased the book and fled the shop before his potion wore off and someone spotted him buying something so stupid. Then it was off to Knockturn to see what he could find about historical Parselmouths.
Anyway, between the pedigrees in Boy Who Lived: Heir of Death and Nature's Nobility, Severus was able to construct a sprawling Potter family tree back to twelfth century Gloucestershire in the male line, to the thirteenth century in the Peverell line, and to the Anglo-Saxon invasion in the Black line which was the oldest. Technically, the Ollivander connection was older, the family having been well established in Brittannia even before the Roman conquest, but the last time an Ollivander had made it into the pedigree was an affair with a Black before the Norman invasion, and other connections were equally speculative. The Ollivander family were distinctly odd, even for wizards, in that they refused to use anything so passé as marriage certificates and direct descendance to track inheritance. Rather, members of the Ollivander family were frequently illegitimate, historically speaking, but were acknowledged as heirs as soon as they demonstrated aptitude for the family business of wand-making. Any children who failed Herbology, Potions, Divinations, or Ancient Runes when they got to Hogwarts was said to take after in-laws and would carry their mother's maiden name instead of the Ollivander name. Or a child might be born to another family, say the Smiths, and then claimed as a prospective Ollivander later when their affinity became clear. It was one of the reasons so many children in the family were illegitimate, since so many other pureblood families were unwilling to countenance a marriage alliance under such an arrangement.
Perusing Nature's Nobility riled up Severus' old sense of jealousy for pureblood elites. Odd. He had thought himself well and truly over it, particularly after the past few years minding the pureblooded orphans in Slytherin House, but apparently the old hurt lingered. The Prince family was a few centuries old - he and Harry were even cousins of some sort. It was a legacy he should have been entitled to, but no. Other than the burst of hate mail he received after his mother's death notice in the paper, the family still pretended the blood relationship did not exist.
He assuaged his spite by spending twenty minutes drawing judgmental little circles around every close-cousin marriage in the Black family tree, culminating in the cursed union that spawned Sirius Black, before setting the ode to pureblood arrogance aside at last.
The book he found in Borgin and Burkes was far more interesting anyway. The Serpent Speaks was actually an attempted dictionary of Parseltongue written by one of the celebrated polyglots in the Crouch family in the early sixteenth century. This was back before the Gaunt family had collapsed and Parseltongue become too suspicious for upstanding wizards to write or indeed own a book about. Sadly, the notation Cleopatra Crouch used for the various sibilants of the language was quite beyond Severus' ability to decipher, but he didn't actually need that. The important part was the introduction, which included a brief history of Parseltongue.
Besides the Gaunt-Slytherin family and Moses, there were about a dozen other famous historical Parselmouths listed. Saint Patrick was the only other notable example in the British Isles. Amusingly, the muggle Christians had his story totally backwards. Patricus son of Calpurnius did not banish the Irish snakes, for there were never any to begin with. Rather, he expressed disappointment on his arrival to Ireland that there were none of his favorite reptiles with which he might more easily effect his escape from the pirates who kidnapped him. Otherwise, there were several members of the Akingbade family in medieval Yoruba, two representatives from the Shafiq family while they were still living in the Abbasid Caliphate (and a debate as to whether the Shafiqs descended from Moses or Herpo the Foul or both), a few Patils in India (unclear which family, as Severus knew there were at least three), and the dragonologist Quong Po in China, with whom Cleopatra Crouch had a a healthy academic correspondence. Quong Po was one of those acknowledged in the book for his contributions to her scholarship.
The book of course did not mention the Parselmouths of the American Sayre or Steward families, off shoots of Slytherin, or the Itzcoatl family in Mexico, because the book was published while the Spanish conquest of the Aztec empire was still unfortunately ongoing. The wizarding community of the Afro-Eurasian landmass had been just as cut off from the Americas as the muggles before the muggle merchants started looking for creative ways to get to India.
Severus only worked on the project in the evenings after returning from Privet Drive, and after he had finished any brewing for the day. It therefore took about a week to finish extracting all the useful information he could from his initial selections. He had yet to identify a known Parselmouth in Harry's direct ancestry, so he returned to Diagon to find biographies of every historical Parselmouth he had identified. It was a moderately successful trip, with at least one book representing each family, doubling his list. He discovered that the lineage of Moses became uncertain after the eighth century BC but that certain Orthodox Jewish families still claimed descent from Moses' elder brother Aharon. The high priests could reportedly heal snake bites or something, so that was a potential lead. There were a few daughters-of-Jacobs married into the Rosier line shortly after their arrival in England that might have been muggleborn or halfblood Jews. He made a note to look into those further if no other likely candidates presented themselves.
The lineage of Herpo the Foul was lost to time, fortunately or unfortunately. Patricus had no known children, but his squib sister Darerca had somewhere between eleven and twenty-one, so that connection may or may not be traceable on the muggle side. Her only known wizarding son managed to become King of the city-state of Ys, but both he and his witch wife and daughter drowned when the low-lying country was catastrophically inundated. The Akingbade family did have one marriage connection to the Shacklebolts in England in the 1700s, but sadly after the last of Harry's Shacklebolt ancestors. The English Shafiqs likewise did not descend from the branch of the family with known Parselmouths. Quong Po did have some distant cousins many generations removed living in the British Isles currently, but none of them seemed to be related to the Potters. It took a ridiculously long time to establish the magical Patil family in England likely had no connection at all to the Patil Parselmouths in India - it was the Hogwarts yearbook of 1807 of all things that finally answered the question. Turns out, the Indian-English magical lineage originated with a muggleborn witch with the surname Banerjee, who married a muggle man Rajesh Patil in the late eighteenth century. Their son managed to become Head Boy and talked about his parents in the brief interview included with his picture. The Patils had yet to marry into the Potter line anyway, so the point was moot. It was just frustrating Severus had expended so much time researching an ancestry that turned out to be irrelevant.
Admiring his large stack of geneological tables and notes on Parselmouths, carefully arranged on Petunia's dining room table that evening, Severus allowed himself a glow of pride in his work. His research had been as thorough as possible without the Ministry's or Gringott's records, either of which would have attracted attention had he tried to access them for the project.
Petunia and Vernon looked over the spread. Petunia snorted in mirth. "Sev, did anyone ever tell you? You are such a swot."
Vernon chuckled.
Severus flushed slightly but kept his voice light as he answered, "Lily might have mentioned it."
The muffled sounds of discontented infant drifted down on them from upstairs. "Oh, thank god," Vernon muttered. "Righto, I've got Dahlia, dear. I'll leave this to you lot." He lumbered out of the room.
Still shaking her head, Petunia hefted a folder containing her part of the research. The tree wasn't quite so extensive as the one Severus had constructed, but she still managed to follow her mother's line back about three hundred years. He was quite impressed, actually, since most muggles weren't so obsessed with ancestry as pureblooded wizards tended to be. Plus, she was busier than he was at the moment. "How did you manage to get so much data so quickly with everything else on your plate?"
She snorted. "I looked through mum's old address book and called my grandmother's cousin Beverly. She's eighty-five and was treasurer for the local genealogical society in Cokeworth for something like ten years. I remember being dragged to one of the meetings when I was little. She had all this to hand in boxes in her spare room, just wrote up a tree for me with dates and any known place names. The hardest part was getting off the phone, honestly. She doesn't get many callers any more."
"I see."
"You'll find this part interesting," Petunia said, pointing to a name about two-thirds of the way up the page. He glanced down and read the name Thomas Hodgeson, married to a Roberta Snape. He stared at it a moment in surprise before looking up at Petunia again. They had speculated before about the possibility of being distant cousins, but he hadn't expected to turn up actual evidence for it, somehow.
"Any relation?" he asked casually.
She nodded, eyes bright with glee to have caught him by surprise. "Your great-great-great-great-great-great-great-great aunt, I believe." He blinked. She smirked. "I asked Aunt Beverly when I saw the name, mentioned that you and Lily were childhood friends but not that I still knew you."
"How many greats?"
"Seven."
"Right. Er, so that makes us..."
"It's actually sixth cousins twice removed, according to my aunt."
"I see... I think that's closer than I am to Harry on the wizarding side, funnily enough."
"You're technically the generation below Harry's," she continued, finally passing him the paper detailing the last two centuries of his own family, or at least those with the Snape surname. "The Snapes married younger than the Hodgesons."
He blinked again and looked down at the paper, reading the names he had so rarely heard before. Severus was an only child. His father had been the youngest of four, his eldest brother being imprisoned for longer than Severus had been alive and the other two dying of a muggle childhood illness - measles? Severus' grandfather and great-uncles had all been killed in World War II, and he barely knew their names. Nor had he ever met his cousins by their younger sister... He was so used to thinking of himself as a man with no family left, it was strange to think there actually were still muggle Snapes up in Cokeworth. Or at least, there were at some point. The younger generation could well have moved out of the dying town by now.
Petunia cleared her throat. "Sev? Shall we get to it? I should really go to bed soon."
"Of course." He launched into an explanation of his notes on the Potter family, just a quick summary and swift conclusion that there was no provable link to known historical Parselmouths. He then produced the notes on Patricus and the possible Rosier-Jewish connection as potential avenues of research on the muggle side. When he was finished, Petunia pursed her lips.
"You disagree?" he prompted.
"Well, not as such. You're probably right, those two are the best bets for finding something, since the Gaunt family tree is so, er, linear. I just... it would be a lot of work to try to trace a random thirteenth century Jacob back to the high priests of ancient Israel. And the family records in the British Isles just aren't reliable back that far, not even for the nobility. I mean, you're trying to trace back to Roman Britain. I don't think it's possible. It's frankly ridiculous you can follow the wizard lines back so far."
"True, it is," Severus agreed.
"I don't think I would be all that reassured even if we did find a provable Parselmouth connection at this point. It would be too far back, the relation too tenuous for me to trust that's the cause."
"Also true. I suppose I'll have to look into the possibility of magical residue more instead." He glared at the pile of useless paper.
Petunia patted his hand. "Try not to set it on fire with your mind, Sev. I still appreciate all the work you went to. And it won't go to waste."
"Oh?"
"Sure. We can't prove a connection to a Parselmouth, but by the same token, I'll wager no one on your side can disprove it either. So if it ever comes out, we'll claim that Jacob of Suffolk was a descendant of Moses' brother Aharon, and that my Irish great-great grandmother Moreen was a descendant of Saint Dererca. Who's to claim otherwise? Especially when we've got such a well-researched and well-documented tree for the rest of it."
It was Severus' turn to grin at Petunia's scheme. The hat certainly Sorted her correctly. "Good point."
Upstairs, the whimpers that Vernon had to this point successfully soothed burst out into full-blown wails, and Severus could hear Vernon hastily moving about to take the infant downstairs before she managed to wake Harry and Dudley. He'd come to recognize the pattern well after the last few weeks. He grinned and glanced at Petunia.
He was caught by her expression, neither merry nor knowing nor even wry but rather dim and tired. She saw him looking and smiled, but it didn't reach her eyes. And mind-wizard that he was, he could not help in that moment but see into the thoughts she tried to hide with smiles and happy platitudes for her children. What he saw was not mere late-night fatigue but an aching weariness, self-doubt, and worry with no conscious hope for reprieve. He reared back involuntarily at the unexpected insight. Quickly and deliberately closed his mind to her unguarded thoughts.
"What's wrong?" he asked without thinking.
"Nothing," she said, wrinkling her forehead.
"No, you're..." he trailed off, unsure what to say, unsure whether to admit he'd accidentally seen what should be private. "Worried," he finished lamely.
"Of course I'm worried. About Harry," she said shortly. She turned towards Vernon as soon as he entered the room, cooing at squalling Dahlia, offering her loving arms to her baby.
Severus kept watching her. Perhaps. Perhaps her worry was all for Harry, but the intensity... That was the reason he had caught it when her expressions and body language were hiding it, when he wasn't using deliberate Legilimency to look for it.
"Sev?"
He startled, realizing he'd missed her speaking to him.
"Pack this up will you? I don't want the magic stuff lying around where the boys might come across it. They're starting to sound out words, and you know Harry will immediately be into anything he realizes you left here."
"Of course." His hands moved automatically, while his eyes still studied her face, looking for hints explaining what he'd seen. But no, it was all light again, now she had her defenses back up. He wouldn't look again; that would be unspeakably rude and probably ruin their relationship. But he'd pay closer attention in the future. He'd lost Lily and his own mother - he needed Petunia to stay happy and healthy.
When he was still sitting at the table a few minutes later as Petunia and Vernon started to go upstairs, Petunia looked back at him with faint irritation in her arched eyebrow. "Goodnight, Sev."
"Right. Sorry. Goodnight."
Author's note: Most everyone has an Aunt Beverly genealogy nut somewhere in the family. The Ollivander thing is entirely made up by me, just a reason for them to be weird and hard to track family-wise. Cleopatra Crouch is made up, chose the name because the famous Queen Cleopatra was herself a polyglot. And alliteration, obviously. Wizards like alliterative names. I have no intention to offend religious devotees. The incorporation of mystical figures from both Judaism and Catholicism into wizarding history is instead an acknowledgment of the historical prominence of religion and the fact that secular society as we understand it didn't really exist until the modern period. Wizards were not always cut off from the rest of the world, and there's no evidence in canon that they were all pagan. Thanks for all the reviews!