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\title{What the Garum Vat Left Behind}
\author{The Science Journaling Club}
\date{Field Notes --- Paper Analysis --- Archaeogenetics}

\begin{document}
\maketitle

\begin{abstract}
Garum was Roman fish sauce, made by salting small fish and letting them rot
on purpose, and it was manufactured at industrial scale on the Atlantic coast
of Iberia for centuries. What was left in the vats afterward was never meant
to be looked at closely: crushed bone, digested by its own sauce, sitting for
months in salt, acid and other creatures' enzymes. In 2025 a team led by
Gon\c{c}alo Espregueira Themudo sequenced it anyway. From bone fragments in a
vat at Adro Vello, Galicia, dated to the first to third centuries AD, they
recovered enough DNA to confirm the fish was European sardine
(\textit{Sardina pilchardus}) and to go further than bone shape ever could:
placing those Roman-period sardines inside the species' modern population
structure \cite{themudo2025}. Eighteen bone samples went in; seventeen came
out sequenced, one discarded; endogenous sardine DNA ran from 4\% to 21\% of
all reads, mitochondrial coverage from $1.3\times$ to $197.6\times$. Set
against 108 modern reference mitogenomes spanning the species' Atlantic and
Mediterranean range, the Adro Vello sardines cluster with today's Central
Atlantic group --- Iberia, Morocco and the French coast --- but noticeably
less admixed than the modern population sampled from the same waters. This
Field Note is about how you pull a population history out of something a
Roman worker threw away as sludge, and what a tighter, less-mixed sardine
population implies about how a fishing fleet without engines actually worked
its coast.
\end{abstract}

%============================================================================
\section{The Smelliest Sample in Archaeology}

Picture the actual object first, because the paper is really about the
object. A Roman fish-salting works on the Galician coast, four rectangular
vats cut into rock and lined with waterproof plaster, standing empty for
seventeen hundred-odd years and then excavated. Vat one still held the bottom
of what had been in it: a compacted mass of crushed fish bone and vertebrae,
residue from a batch of garum ladled off as liquid centuries ago, leaving
behind what nobody bothered to take with them.

Every step that produced this material was designed, more or less by
accident, to be bad for DNA. The fish were gutted and packed in salt. They
were crushed, deliberately, to speed up the process. They sat in their own
acids and in the digestive activity of microorganisms for weeks or months, at
ambient outdoor temperature. Compare that to how most ancient DNA is
recovered --- a buried skeleton, protected by soil, cool, dark and
un-fermented. Garum residue is close to the worst realistic substrate you
could hand a molecular lab and still call bone.

A team led by Themudo sequenced it anyway, and published the result in
\textit{Antiquity} in the summer of 2025 --- not as a curiosity, but as a
demonstration that an entire category of archaeological material, industrial
fish-processing waste sitting in storage boxes at excavated sites across the
former Roman world, might be usable for population genetics after all
\cite{themudo2025}.

%============================================================================
\section{What Garum Actually Was}

Garum is usually introduced to modern readers as a punchline: the Romans put
rotten fish sauce on everything. That undersells it. It was closer to what
fish sauce is in parts of Asian cuisine today --- a fermented, intensely
savoury condiment used constantly, in small amounts, across a huge range of
dishes, made in enormous industrial quantities and shipped around the
Mediterranean and Atlantic in amphorae as one of the most heavily traded
foodstuffs of the Roman world.

Curtis's standard economic history of the industry lays out the production
logic: small pelagic fish, whichever species schooled abundantly and cheaply
near a given coast, were mixed with salt at a preserving ratio and left to
autolyze, their own digestive enzymes and ambient microbes breaking the flesh
down over weeks in the sun, before the liquid was drawn off and graded by
quality --- garum and liquamen at the top, the paste left behind sold on as
allec for people who could not afford the good stuff \cite{curtis1991,
grainger2020}. This was not a cottage industry. The archaeological record
includes fish-salting complexes with dozens of vats standing along entire
stretches of coastline, from Baetica in southern Spain up through Lusitania
and Galicia to Brittany, exporting a manufactured commodity the way an
olive-oil or wine estate did \cite{bernal2018, marzano2013}.

Which species went into a given vat depended almost entirely on what a
coastal fleet could catch locally and cheaply, in bulk, without
refrigeration. That is exactly the kind of decision archival texts rarely
record and bone morphology only sometimes settles, and exactly the kind of
decision population genetics can speak to, because a fishery's catch carries
the genetic signature of the population it was drawn from.

%============================================================================
\section{Four Vats on a Galician Headland}

\begin{table}[htbp]
\centering
\small
\begin{tabular}{ll}
\toprule
\textbf{Site} & Adro Vello, O Grove, Galicia, NW Iberia \\
\textbf{Facility} & Roman \textit{cetaria} (fish-salting works), four large vats \\
\textbf{Sample source} & Crushed fish bone/vertebra residue, vat one \\
\textbf{Radiocarbon age} & $2280 \pm 30$ BP \\
\textbf{Calibrated, 68.2\%} & cal AD 162--321 \\
\textbf{Calibrated, 95.4\%} & cal AD 84--394 \\
\textbf{Occupation phase} & Fish-salting use, 1st--3rd centuries AD \\
\bottomrule
\end{tabular}
\caption{Site record. Source: \cite{themudo2025}.}
\label{tab:site}
\end{table}

Adro Vello sits on the O Grove peninsula, the north-westernmost corner of
Iberia, a stretch of Atlantic coast that supported a dense chain of Roman
fish-processing sites from roughly the first century AD onward. The site had
already been excavated and its stratigraphy worked out before this study;
what changed in 2025 was somebody deciding the sludge at the bottom of vat
one was worth a DNA extraction rather than a discard bag \cite{themudo2025}.

\paragraph{Club arithmetic, not the paper's.} Subtract those calibrated
ranges from the present. Cal AD 84--394, the wide 95.4\% interval, is roughly
1{,}632 to 1{,}942 years before 2026. The tighter 68.2\% interval, cal AD
162--321, is roughly 1{,}705 to 1{,}864 years before 2026. Loosely rounded,
that is the same ``about seventeen hundred years old'' figure that circulates
in casual summaries of this kind of find --- it sits at the young edge of the
tighter interval, not its centre, but it is not a wrong rounding, just an
optimistic one.

\begin{figure}[htbp]
\centering
\begin{tikzpicture}
\begin{axis}[
  width=13cm, height=4.2cm,
  xmin=0, xmax=500, ymin=0, ymax=1,
  xlabel={year AD}, ytick=\empty,
  axis y line=none,
  axis x line=bottom,
  xtick={0,100,200,300,400,500},
  enlargelimits=false,
]
\addplot[fill=clay, fill opacity=0.28, draw=none] coordinates {(84,0.45) (394,0.45) (394,0.75) (84,0.75)} \closedcycle;
\addplot[fill=clay, fill opacity=0.9, draw=none] coordinates {(162,0.45) (321,0.45) (321,0.75) (162,0.75)} \closedcycle;
\addplot[brine, line width=3pt, mark=none] coordinates {(0,0.15) (300,0.15)};
\node[font=\scriptsize] at (axis cs:239,0.90) {95.4\%: cal AD 84--394};
\node[font=\scriptsize, white] at (axis cs:241,0.60) {68.2\%: AD 162--321};
\node[font=\scriptsize, brine, anchor=north] at (axis cs:150,0.10) {fish-salting occupation, 1st--3rd c. AD};
\end{axis}
\end{tikzpicture}
\caption{The two calibrated radiocarbon ranges reported for vat one, drawn to
the site's broader fish-salting occupation phase. The tight 68.2\% interval
sits comfortably inside the first-to-third-century occupation window. Source:
\cite{themudo2025}; club arithmetic converts this to roughly
1{,}632--1{,}942 years before 2026.}
\label{fig:chronology}
\end{figure}

%============================================================================
\section{Why Nobody Expected DNA to Survive This}

Ancient DNA degrades by a handful of well-understood mechanisms, and garum
production hits several of them at once. The fermentation process itself
creates an acidic environment, which speeds up depurination --- the loss of
purine bases from the DNA backbone that leaves the molecule prone to breaking
at that exact point --- and therefore accelerates fragmentation beyond what
age alone would produce \cite{themudo2025}. Whatever microbial community did
the fermenting also brought its own endonucleases, enzymes that cut DNA,
adding a second and independent route to degradation on top of ordinary
chemical decay.

Stack that on top of the crushing and centuries of salt exposure, and the
honest prior going into this project was that there might be nothing left
worth sequencing. The reason it worked at all is the same reason ancient DNA
work in general has improved dramatically over the last decade: shotgun
sequencing does not need long, intact strands. It needs enough short
fragments, however degraded, to pile up into confident coverage once you have
enough of them and a reference genome to map them against.

%============================================================================
\section{From Crushed Bone to Sequencer}

The wet-lab side of this is standard ancient-DNA protocol, chosen
specifically because it tolerates degraded material. Bone samples were
extracted using a buffer built around EDTA and proteinase K --- EDTA to
chelate the calcium locking DNA inside bone's mineral matrix, proteinase K to
digest the collagen holding everything together --- then built into
double-stranded Illumina sequencing libraries and run through shotgun
sequencing on a NovaSeq X.

Shotgun sequencing, rather than targeting specific genes, sequences whatever
DNA is in the tube: sardine DNA, bacterial DNA from the fermentation
microbiome, environmental DNA, human DNA from centuries of handling. Only a
fraction of any sequencing run belongs to the fish you actually care about.
That fraction is the endogenous DNA percentage, and it is the first number
that tells you whether an extraction was worth the reagents:
\begin{equation}
\text{endogenous DNA \%} \;=\; \frac{\text{reads mapping to the sardine reference genome}}{\text{total sequenced reads}} \times 100 .
\end{equation}

From there, mapped reads were run through ANGSD for genotype likelihoods,
consensus sequence calling and SNP discovery \cite{angsd2014}, mitochondrial
genomes were assembled and placed on a phylogeny with BEAST
\cite{beast2019}, nuclear population structure was estimated with PCAngsd and
NGSadmix \cite{pcangsd2018, ngsadmix2013}, and relationships among
mitochondrial haplotypes were visualised as a median-joining network in
PopART \cite{popart2015} --- tools built specifically for the low- and
uneven-coverage data that ancient samples produce, where you often cannot
call a genotype with confidence at every site and have to work with the
probability of one instead.

%============================================================================
\section{Proving the DNA Was Actually Roman}

None of that matters if the DNA in the tube is modern contamination rather
than the Roman-era fish. Ancient DNA has a signature that contamination does
not: over centuries, cytosine bases near the ends of DNA fragments deaminate
into uracil, which sequencing machinery reads as thymine, producing a
characteristic excess of C-to-T substitutions concentrated at the start of
sequencing reads and tapering off toward the middle. The paper reports
exactly this pattern, checked with DamageProfiler \cite{damageprofiler2021},
the standard software for quantifying it. A modern contaminant fragment does
not carry that damage signature; an authentically old one does, reliably,
because deamination is a slow chemical clock that keeps ticking as long as
the molecule exists.

\begin{figure}[htbp]
\centering
\begin{tikzpicture}
\begin{axis}[
  width=12cm, height=6cm,
  xmin=0, xmax=30, ymin=0, ymax=0.30,
  xlabel={position from the 5$'$ end of the read (bases)},
  ylabel={C$\to$T misincorporation rate},
  ymajorgrids=true, grid style={dashed, gray!30},
  legend style={font=\scriptsize, at={(0.98,0.97)}, anchor=north east}
]
\addplot[clay, line width=1.6pt, mark=*, mark size=1.6pt] coordinates {
  (0,0.27) (1,0.20) (2,0.135) (4,0.075) (6,0.045) (10,0.022) (15,0.015) (20,0.013) (30,0.012) };
\addlegendentry{authentic ancient signal}
\addplot[brine, line width=1.4pt, dashed, mark=none] coordinates { (0,0.012) (30,0.012) };
\addlegendentry{flat background (modern contamination)}
\draw[gray, dashed] (axis cs:10,0) -- (axis cs:10,0.30);
\node[font=\scriptsize, gray, anchor=west] at (axis cs:10.5,0.20) {background reached by $\sim$position 10};
\end{axis}
\end{tikzpicture}
\caption{The general shape of the test, not a redrawn result. Real ancient
DNA shows an elevated C-to-T misincorporation rate concentrated at the very
start of a sequencing read, decaying to background within the first several
bases --- the signature of centuries of cytosine deamination. The paper
reports finding this pattern in the Adro Vello reads via DamageProfiler
\cite{damageprofiler2021}; this figure illustrates the generic shape of that
kind of curve, since exact per-position rates were not part of what we could
confirm from the published record.}
\label{fig:damage}
\end{figure}

\begin{quote}
\small\itshape This is worth sitting with for a second. The same acidic,
enzyme-rich environment that nearly destroyed the DNA also, ironically,
cannot fake its age. Depurination breaks the molecule; deamination marks the
pieces that survive. The garum vat did both, and only one of them is a
problem.
\end{quote}

%============================================================================
\section{The Ledger: Eighteen Fragments, Twelve Genomes}

\begin{table}[htbp]
\centering
\small
\begin{tabular}{ll}
\toprule
\textbf{Bone samples extracted} & 18 \\
\textbf{Sequenced successfully} & 17 (1 discarded) \\
\textbf{Deep-sequenced for nuclear analysis} & 12 \\
\textbf{Endogenous sardine DNA} & 4\% to 21\% of reads \\
\textbf{Mitochondrial coverage} & mean $1.3\times$ to $197.6\times$ \\
\textbf{Nuclear genome coverage} & $1.1\times$ to $3.7\times$ \\
\bottomrule
\end{tabular}
\caption{Extraction ledger, vat one, Adro Vello. Source: \cite{themudo2025}.}
\label{tab:ledger}
\end{table}

\paragraph{Club arithmetic on the paper's own counts.} $17/18 = 94.4\%$ of
extractions produced usable sequence, an unusually good hit rate for a
substrate this hostile. Of those, $12/17 \approx 70.6\%$ had enough material
to justify the deeper sequencing needed for nuclear population genetics
rather than mitochondrial genealogy alone. The spread inside that success is
enormous: the best-preserved fragment yielded a mitochondrial depth
$197.6 / 1.3 \approx 152\times$ higher than the worst, and an endogenous DNA
fraction $21/4 = 5.25\times$ higher. Same vat, same species, wildly different
survival --- which is itself a finding, since preservation inside one deposit
is not a single number you can assume in advance.

\begin{figure}[htbp]
\centering
\begin{tikzpicture}
\begin{axis}[
  width=12cm, height=4.6cm,
  xbar, xmin=0, xmax=20,
  y=0.9cm,
  symbolic y coords={deep-sequenced (nuclear), sequenced, extracted},
  ytick=data,
  nodes near coords, nodes near coords align={horizontal},
  xlabel={number of bone samples}
]
\addplot[fill=clay, fill opacity=0.85] coordinates {(18,extracted) (17,sequenced) (12,deep-sequenced (nuclear))};
\end{axis}
\end{tikzpicture}
\caption{The extraction funnel: eighteen fragments went in, seventeen were
sequenced (one discarded), and twelve reached the depth needed for nuclear
population genetics. Endogenous DNA ran 4--21\% of reads; mitochondrial depth
spanned $1.3\times$--$197.6\times$; nuclear depth spanned
$1.1\times$--$3.7\times$. Source: \cite{themudo2025}.}
\label{fig:funnel}
\end{figure}

%============================================================================
\section{A Name Bones Already Half-Knew}

It would be a cleaner story if the DNA revealed a species nobody suspected.
It did not, quite, and the honest version of that is more interesting than a
reveal would have been. Morphological analysis of the Adro Vello bones had
already identified the assemblage as mostly \textit{Sardina pilchardus},
European sardine, without attaching a firm percentage to that call
\cite{themudo2025}. Crushed, salted, partially digested vertebrae are hard to
measure with confidence; ``mostly sardine'' was a reasonable read of the bone
shapes available, not a number anyone could defend to a second decimal
place.

Two other Roman Atlantic fish-salting sites had already done better than
that, because their assemblages were less processed. At La Falaise, a site
at \'Etel on the French Atlantic coast, vat one's fish remains were counted
directly: 99.6\% European sardine, split between Atlantic herring, whiting
and Atlantic mackerel. At Bel\'em, in Portugal, sardine came out above 98\%
of recovered material, with anchovy, Atlantic horse mackerel, mackerel and
Mediterranean moray making up the rest \cite{themudo2025}. Those numbers
exist because those bones were countable in a way Adro Vello's were not.

\begin{figure}[htbp]
\centering
\begin{tikzpicture}
\begin{axis}[
  width=12cm, height=6cm,
  ybar, bar width=32pt,
  symbolic x coords={La Falaise, Bel\'em, Adro Vello},
  xtick=data,
  ymin=0, ymax=105,
  ylabel={\% sardine, by bone count},
]
\addplot[fill=fcentral, fill opacity=0.85] coordinates {(La Falaise,99.6) (Bel\'em,98)};
\addplot[draw=clay, pattern=north east lines, pattern color=clay] coordinates {(Adro Vello,74)};
\node[font=\scriptsize] at (axis cs:La Falaise,103) {99.6\%};
\node[font=\scriptsize] at (axis cs:Bel\'em,103) {$>$98\%};
\node[font=\scriptsize] at (axis cs:Adro Vello,80) {``mostly'', no \% reported};
\end{axis}
\end{tikzpicture}
\caption{Two neighbouring Roman Atlantic sites had bones intact enough to
count directly, and both came back overwhelmingly sardine. Adro Vello's
bones, crushed and fermented, only supported a qualitative ``mostly
sardine'' call from morphology \cite{themudo2025} (the hatched bar's height
is arbitrary; no percentage was reported). The DNA work does not really
compete with the counting done at La Falaise or Bel\'em; it answers a
question neither of those counts could ever reach.}
\label{fig:dominance}
\end{figure}

%============================================================================
\section{Where in the Atlantic These Fish Belonged}

Here is the actual novelty, and the paper says so itself: this is about
moving past species identification into population range and admixture,
something no amount of staring at a vertebra can do \cite{themudo2025}. A
bone tells you what animal it came from. It cannot tell you which breeding
population that animal belonged to, whether it was a local resident or a
long-distance migrant, or how connected its population was to the ones along
the neighbouring coast.

To ask the population question, the team compared their ancient mitogenomes
and nuclear SNPs against 108 modern reference sardine mitogenomes spanning
the species' known range, grouped into four broad geographic clusters used in
prior sardine population genomics: a Western group, a Central group covering
Morocco, Iberia and Atlantic France, a Mediterranean group, and a Canary
Islands group \cite{dafonseca2024}. Running principal component analysis with
PCAngsd on the combined dataset, PC1 captured 7.3\% of total genetic variance
and PC2 a further 1.2\% \cite{themudo2025, pcangsd2018}.

\paragraph{Club arithmetic.} PC1 plus PC2 together account for only
$7.3\% + 1.2\% = 8.5\%$ of the variance in the dataset. That is small by the
standards of, say, human population genetics, where the first couple of axes
in a similarly structured sample can carry far more. It is not a weakness in
this analysis; it is a known feature of small pelagic marine fish, which tend
to have enormous population sizes and correspondingly weak, slow genetic
drift between regions, so real, meaningful population structure can sit on
top of comparatively little total variance \cite{dafonseca2024}. Low
percentages here are compatible with the clustering being real.

And it was real: on that PCA and in NGSadmix admixture modelling, the Adro
Vello samples fell inside the modern Central group, alongside today's
Iberian, Moroccan and Atlantic French sardines --- the geographically
appropriate cluster for a sardine caught off the Galician coast
\cite{themudo2025, ngsadmix2013}. One sample stood out: specimen 1003 showed
a minor genetic contribution from the Eastern/Mediterranean side of the
species' range, a small signal of gene flow the rest of the assemblage did
not share.

\begin{figure}[htbp]
\centering
\begin{tikzpicture}[scale=1]
\draw[fwest, fill=fwest, fill opacity=0.14] (-3.4,1.3) ellipse (1.9cm and 1.25cm);
\node[fwest, font=\small\bfseries] at (-3.4,1.9) {WESTERN};
\draw[fcentral, fill=fcentral, fill opacity=0.16] (0.4,-0.1) ellipse (2.6cm and 1.8cm);
\node[fcentral, font=\small\bfseries] at (0.4,1.35) {CENTRAL};
\node[font=\scriptsize] at (0.4,1.05) {Morocco / Iberia / Atl. France};
\draw[fmed, fill=fmed, fill opacity=0.14] (3.8,1.5) ellipse (1.8cm and 1.15cm);
\node[fmed, font=\small\bfseries] at (3.8,2.05) {MEDITERRANEAN};
\draw[fcanary, fill=fcanary, fill opacity=0.14] (-1.6,-2.6) ellipse (1.8cm and 1.1cm);
\node[fcanary, font=\small\bfseries] at (-1.6,-3.1) {CANARY ISLANDS};
% ancient cluster
\foreach \x/\y in {0.0/0.1, 0.25/-0.05, 0.5/0.15, -0.15/-0.2, 0.35/0.3, 0.6/-0.1, -0.05/0.3, 0.65/0.1} {
  \fill[clay] (\x,\y) circle (2.1pt);
}
\node[clay, font=\scriptsize\bfseries] at (0.25,0.62) {17 Adro Vello samples};
\node[clay, font=\scriptsize] at (0.25,0.45) {tightly clustered};
\fill[clay] (0.75,0.35) circle (2.1pt);
\draw[fmed, dashed] (0.75,0.35) -- (2.6,1.4);
\node[fmed, font=\scriptsize, align=left, anchor=west] at (2.65,1.4) {sample 1003: minor\\Eastern-group signal};
\end{tikzpicture}
\caption{A schematic, not a redrawn plot: the paper reports that Adro Vello's
ancient sardines cluster with the modern Central Atlantic group and that one
specimen, 1003, carries a minor signal from the Eastern/Mediterranean group
\cite{themudo2025}. Zone shapes and dot positions here are illustrative; only
the grouping itself, and the PC1/PC2 variance figures (7.3\% and 1.2\%), are
the paper's.}
\label{fig:pca}
\end{figure}

%============================================================================
\section{A Population More Isolated Than Today's}

The comparison that makes this more than a species-confirmation exercise is
what happens when you set the ancient cluster against modern sardines sampled
from the same part of the Atlantic. The paper's own description of the
result is direct: the Adro Vello samples are ``much less admixed'' than their
modern western Iberian counterparts \cite{themudo2025}. Roughly, the
Roman-period population reads as more genetically homogeneous, more
internally consistent, less mixed with neighbouring groups than the sardines
swimming off the same coast today.

Two broad explanations are on the table, and the paper does not need to pick
one for the observation to matter. One is that the modern Central Atlantic
sardine population has become more connected to its neighbours over the last
seventeen-odd centuries --- more gene flow in, whether from long-distance
larval drift, changes in ocean currents, or simply a larger, more mobile
modern population mixing more freely across a wider range. The other is more
directly about people: a small-boat, oar-and-sail Roman fishery working a
limited stretch of coastline without refrigeration would have depended on
whatever sardine schools were locally, reliably present, converting live
catch into salted fish within days. A locally resident, less externally
admixed population is exactly the kind of stock such a fishery would both
find and, over generations of harvest, help keep locally rooted. Neither
explanation requires the other to be false.

%============================================================================
\section{What This Says About How Rome Fished}

Take the population result seriously as an economic clue rather than only a
biological one. The scale of the Atlantic garum industry --- the chain of
\textit{cetariae} running from Baetica up through Lusitania and Galicia to
Brittany \cite{bernal2018} --- has always been read primarily from the built
infrastructure: how many vats, how large, how they were plastered and
drained. This paper adds a genetic constraint on the other half of that
system, the part upstream of the vat: the fish themselves, and by extension
the boats and crews that caught them.

A genetically distinct, comparatively closed Central Atlantic sardine
population being harvested at Adro Vello is consistent with a fishery built
around short-range, repeated exploitation of a nearby, locally persistent
stock rather than one drawing opportunistically on whatever schools happened
to be passing through from further afield. That is a modest claim, and the
paper does not push it further into a full economic argument
\cite{themudo2025} --- but it is a genuinely new kind of evidence for an old
question in Roman economic history: was large-scale ancient fishing
sustainable pressure on a stable local resource, or something closer to
sequential exploitation of whatever showed up? A less-admixed ancient
population looks more like the former.

%============================================================================
\section{What the Paper Doesn't Claim}

Worth being precise about the limits here, because it is easy to over-read a
result like this. The study does not reconstruct Roman fishing routes, does
not quantify how large the historical Central Atlantic sardine population
was, and does not claim the modern increase in admixture, if that is what it
is, was caused by any specific event. It is a single vat, at a single site,
with seventeen usable ancient genomes set against a modern reference panel.
The authors' own framing is appropriately restrained: this is a
demonstration that fish-salting residue is a viable, previously overlooked
source of population-genetic data, with one worked example of what that data
can show \cite{themudo2025}.

That restraint is, if anything, the more useful message for anyone thinking
about what comes next. The claim is not ``we solved Roman sardine population
history.'' It is ``this kind of material, previously written off, is
usable,'' which is a much larger and more durable claim, because it is not
about one vat.

%============================================================================
\section{What We Would Want to See Next}

Three things follow fairly directly from a result shaped like this one.
First, more vats: Adro Vello is one site on one coast with one radiocarbon
date range; the Atlantic \textit{cetariae} chain runs for hundreds of
kilometres and several centuries, and each additional assemblage sequenced
turns a single data point into an actual time series of population
structure. Second, other species: sardine dominated this vat and the two
comparison sites, but garum production used whatever was locally abundant,
and mackerel, herring and anchovy residues sitting in the same storage boxes
are, by this paper's logic, equally sequenceable. Third, and most directly
testable, more samples per site: with only seventeen ancient genomes against
108 modern ones, the admixture comparison is suggestive rather than
saturated, and a larger ancient panel would say with more confidence whether
``much less admixed'' is a small-sample artefact or a durable
population-level difference.

None of that requires new technology. It requires somebody with access to
the right storage boxes deciding, the way this team did, that industrial
food waste from two thousand years ago is worth a proteinase K digest.

%============================================================================
\begin{thebibliography}{99}

\bibitem{themudo2025}
Themudo, G.~E., Fern\'andez-Fern\'andez, A., Valle Abad, P., Rodr\'iguez
N\'ovoa, A.~A., Fern\'andez-Rodr\'iguez, C., Gonz\'alez-G\'omez de Ag\"uero,
E., da Fonseca, R.~R. \& Campos, P.~F. (2025).
Roman Atlantic garum: DNA confirms sardine use and population continuity in
north-western Iberia. \textit{Antiquity} 99(406), 1049--1064.
doi:10.15184/aqy.2025.73

\bibitem{curtis1991}
Curtis, R.~I. (1991). \textit{Garum and Salsamenta: Production and Commerce
in Materia Medica}. Brill. doi:10.1163/9789004377264

\bibitem{grainger2020}
Grainger, S. (2020). \textit{The Story of Garum: Fermented Fish Sauce and
Salted Fish in the Ancient World}. Routledge. ISBN 978-1-315-26982-5

\bibitem{bernal2018}
Bernal-Casasola, D., Exp\'osito, J.~A. \& D\'iaz, J.~J. (2018). The Baelo
Claudia paradigm: the exploitation of marine resources in Roman
\textit{cetariae}. \textit{Journal of Maritime Archaeology} 13(3), 329--351.
doi:10.1007/s11457-018-9209-z

\bibitem{marzano2013}
Marzano, A. (2013). \textit{Harvesting the Sea: The Exploitation of Marine
Resources in the Roman Mediterranean}. Oxford University Press.

\bibitem{angsd2014}
Korneliussen, T.~S., Albrechtsen, A. \& Nielsen, R. (2014). ANGSD: analysis
of next generation sequencing data. \textit{BMC Bioinformatics} 15, 356.
doi:10.1186/s12859-014-0356-4

\bibitem{beast2019}
Bouckaert, R., Vaughan, T.~G., Barido-Sottani, J., Duch\^ene, S., Fourment,
M., Gavryushkina, A., Heled, J., Jones, G., K\"uhnert, D., De Maio, N.,
Matschiner, M., Mendes, F.~K., M\"uller, N.~F., Ogilvie, H.~A., du Plessis,
L., Popinga, A., Rambaut, A., Rasmussen, D., Siveroni, I., Suchard, M.~A.,
Wu, C.-H., Xie, D., Zhang, C., Stadler, T. \& Drummond, A.~J. (2019). BEAST
2.5: an advanced software platform for Bayesian evolutionary analysis.
\textit{PLOS Computational Biology} 15, e1006650.
doi:10.1371/journal.pcbi.1006650

\bibitem{pcangsd2018}
Meisner, J. \& Albrechtsen, A. (2018). Inferring population structure and
admixture proportions in low-depth NGS data. \textit{Genetics} 210, 719--731.
doi:10.1534/genetics.118.301336

\bibitem{damageprofiler2021}
Neukamm, J., Peltzer, A. \& Nieselt, K. (2021). DamageProfiler: fast damage
pattern calculation for ancient DNA. \textit{Bioinformatics} 37, 3652--3653.
doi:10.1093/bioinformatics/btab190

\bibitem{ngsadmix2013}
Skotte, L., Korneliussen, T.~S. \& Albrechtsen, A. (2013). Estimating
individual admixture proportions from next generation sequencing data.
\textit{Genetics} 195, 693--702. doi:10.1534/genetics.113.154138

\bibitem{dafonseca2024}
da Fonseca, R.~R., Campos, P.~F., Rey-Iglesia, A., Barroso, G.~V., Bergeron,
L.~A., Nande, M., Tuya, F., Abidli, S., P\'erez, M., Riveiro, I., Carrera,
P., Jurado-Ruzafa, A., Santamar\'ia, M.~T.~G., Faria, R., Machado, A.~M.,
Fonseca, M.~M., Froufe, E. \& Castro, L.~F.~C. (2024). Population genomics
reveals the underlying structure of the small pelagic European sardine and
suggests low connectivity within Macaronesia. \textit{Genes} 15, 170.
doi:10.3390/genes15020170

\bibitem{popart2015}
Leigh, J.~W. \& Bryant, D. (2015). POPART: full-feature software for
haplotype network construction. \textit{Methods in Ecology and Evolution} 6,
1110--1116. doi:10.1111/2041-210X.12410

\end{thebibliography}

\end{document}