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One-line summary: Detect cognates, model sound correspondences, infer phylogenetic language trees, and compute lexicostatistical distances from Swadesh list data using LingPy and scipy.
When to Use This Skill
When computing cognate sets from multilingual Swadesh list data
When detecting regular sound correspondences between language pairs
When inferring phylogenetic trees using Neighbor Joining or UPGMA
When computing lexicostatistical distances (% shared cognates)
When reconstructing Proto-language vocabulary via the comparative method
When building distance matrices for historical subgrouping
Identify cognates (words inherited from a common ancestor)
Establish regular sound correspondences
Reconstruct Proto-language phonemes (via the correspondence sets)
Propose a subgrouping based on shared innovations
Lexicostatistics / Glottochronology
Estimate time depth from percentage of shared cognates on Swadesh 100/200-word list.
Swadesh formula: $t = \frac{\ln C}{\ln r}$ where $C$ = proportion of cognates, $r$ = retention rate per millennium (~0.86 for basic vocabulary).
Edit Distance for Cognate Detection
Normalized Levenshtein distance between IPA transcriptions is used as a proxy for cognate probability. Words with distance < threshold (typically 0.5–0.6 after alignment) are candidate cognates.
Step 1: Swadesh List Analysis and Lexicostatistics
import pandas as pd
import numpy as np
import matplotlib.pyplot as plt
from scipy.cluster.hierarchy import dendrogram, linkage
from scipy.spatial.distance import squareform
# ------------------------------------------------------------------ ## Swadesh 50-word list for Indo-European languages (simplified)# Words represented as phonemic transcriptions# ------------------------------------------------------------------ ## Sample of Swadesh concepts (concept: {language: IPA form})
swadesh_data = {
'one': {'Latin':'uːnus', 'French':'œ̃', 'Spanish':'uno', 'Italian':'uno',
'German':'aɪ̯ns', 'English':'wʌn', 'Dutch':'eːn'},
'two': {'Latin':'duːo', 'French':'dø', 'Spanish':'dos', 'Italian':'due',
'German':'tsvaɪ̯', 'English':'tuː', 'Dutch':'tweː'},
'water': {'Latin':'akʷa', 'French':'oː', 'Spanish':'aɣwa', 'Italian':'akːwa',
'German':'vasɐ', 'English':'wɔːtɐ', 'Dutch':'vatɛr'},
'fire': {'Latin':'ignis', 'French':'fø', 'Spanish':'fweɣo', 'Italian':'fwɔːko',
'German':'fɔʏ̯ɐ', 'English':'faɪ̯ɐ', 'Dutch':'vuːr'},
'mother': {'Latin':'maːter', 'French':'mɛːr', 'Spanish':'maðre', 'Italian':'madːre',
'German':'mutɐ', 'English':'mʌðɐ', 'Dutch':'moːdɛr'},
'father': {'Latin':'pater', 'French':'pɛːr', 'Spanish':'padre', 'Italian':'padre',
'German':'fatɐ', 'English':'fɑːðɐ', 'Dutch':'vadɛr'},
'eye': {'Latin':'okulus', 'French':'œɪ̯', 'Spanish':'oxo', 'Italian':'okːjo',
'German':'aʊ̯ɡə', 'English':'aɪ̯', 'Dutch':'oːɣ'},
'new': {'Latin':'nowus', 'French':'nɔf', 'Spanish':'nweβo', 'Italian':'nwɔvo',
'German':'nɔʏ̯', 'English':'njuː', 'Dutch':'niuː'},
'night': {'Latin':'noks', 'French':'nɥɪ̯', 'Spanish':'notʃe', 'Italian':'notːe',
'German':'naxt', 'English':'naɪ̯t', 'Dutch':'naxt'},
'sun': {'Latin':'soːl', 'French':'sɔlɛɪ̯', 'Spanish':'sol', 'Italian':'sole',
'German':'zɔnə', 'English':'sʌn', 'Dutch':'zɔn'},
}
languages = ['Latin', 'French', 'Spanish', 'Italian', 'German', 'English', 'Dutch']
n_langs = len(languages)
n_concepts = len(swadesh_data)
# ---- Compute normalized edit distances -------------------------- #defnormalized_edit_distance(s1, s2):
"""Levenshtein distance normalized by max length."""
m, n = len(s1), len(s2)
if m == 0and n == 0:
return0.0
dp = [[0]*(n+1) for _ inrange(m+1)]
for i inrange(m+1): dp[i][0] = i
for j inrange(n+1): dp[0][j] = j
for i inrange(1, m+1):
for j inrange(1, n+1):
dp[i][j] = dp[i-1][j-1] if s1[i-1] == s2[j-1] else1 + min(dp[i-1][j], dp[i][j-1], dp[i-1][j-1])
return dp[m][n] / max(m, n)
# Pairwise distance matrix (averaged over all concepts)
dist_matrix = np.zeros((n_langs, n_langs))
cognate_matrix = np.zeros((n_langs, n_langs)) # 1 = likely cognate (dist < 0.5)for i, lang1 inenumerate(languages):
for j, lang2 inenumerate(languages):
if i == j:
continue
dists = []
for concept, words in swadesh_data.items():
d = normalized_edit_distance(words[lang1], words[lang2])
dists.append(d)
dist_matrix[i, j] = np.mean(dists)
cognate_matrix[i, j] = np.mean([d < 0.5for d in dists])
print("Normalized phonological distance matrix:")
df_dist = pd.DataFrame(dist_matrix, index=languages, columns=languages)
print(df_dist.round(3))
print("\nEstimated % shared cognates (dist < 0.5):")
df_cog = pd.DataFrame(cognate_matrix * 100, index=languages, columns=languages)
print(df_cog.round(1))
# ---- Glottochronological time estimates ----------------------- #
r = 0.86# Swadesh retention rate per millenniumprint("\nEstimated divergence times (millennia BP):")
for i, lang1 inenumerate(languages):
for j, lang2 inenumerate(languages):
if j <= i:
continue
pct_cognates = cognate_matrix[i, j]
if pct_cognates > 0:
t = np.log(pct_cognates) / np.log(r)
print(f" {lang1}–{lang2}: {t:.1f} millennia ({pct_cognates*100:.0f}% cognates)")
Step 2: Phylogenetic Tree Inference
import numpy as np
import matplotlib.pyplot as plt
from scipy.cluster.hierarchy import dendrogram, linkage, to_tree
from scipy.spatial.distance import squareform
# ------------------------------------------------------------------ ## Infer language phylogeny using Neighbor Joining (via UPGMA here)# ------------------------------------------------------------------ ## Use the distance matrix computed above
condensed = squareform(dist_matrix)
# UPGMA linkage (approximates neighbor joining for well-nested data)
Z = linkage(condensed, method='average')
fig, ax = plt.subplots(figsize=(9, 6))
dendrogram(
Z,
labels=languages,
orientation='right',
leaf_font_size=12,
color_threshold=0.4,
ax=ax,
)
ax.set_xlabel("Phonological distance")
ax.set_title("Indo-European Language Phylogeny\n(UPGMA based on Swadesh list edit distances)")
ax.grid(axis='x', alpha=0.3)
plt.tight_layout()
plt.savefig("language_phylogeny.png", dpi=150)
plt.show()
print("""
Expected subgroupings:
Romance: French, Spanish, Italian (← Latin)
Germanic: German, English, Dutch
Outlier: Latin (ancestor)
""")
# ---- Bootstrap support ----------------------------------------- #
n_boot = 100
np.random.seed(42)
concepts = list(swadesh_data.keys())
n_concepts = len(concepts)
bootstrap_distances = []
for _ inrange(n_boot):
# Resample concepts with replacement
sample_concepts = np.random.choice(concepts, n_concepts, replace=True)
dist_boot = np.zeros((n_langs, n_langs))
for i, lang1 inenumerate(languages):
for j, lang2 inenumerate(languages):
if i == j:
continue
dists = [normalized_edit_distance(swadesh_data[c][lang1], swadesh_data[c][lang2])
for c in sample_concepts]
dist_boot[i, j] = np.mean(dists)
bootstrap_distances.append(dist_boot)
# Compute bootstrap support for Romance clade (French, Spanish, Italian)
romance = ['French', 'Spanish', 'Italian']
romance_idx = [languages.index(l) for l in romance]
non_romance_idx = [i for i inrange(n_langs) if i notin romance_idx]
romance_support = 0for d in bootstrap_distances:
# Check if Romance languages cluster together (internal distances < Romance-Germanic distances)
romance_internal = np.mean([d[i,j] for i in romance_idx for j in romance_idx if i!=j])
romance_external = np.mean([d[i,j] for i in romance_idx for j in non_romance_idx])
if romance_internal < romance_external:
romance_support += 1print(f"Bootstrap support for Romance clade: {romance_support}/{n_boot} ({romance_support:.0f}%)")
Step 3: Sound Correspondence Detection
import pandas as pd
import numpy as np
from collections import defaultdict
# ------------------------------------------------------------------ ## Identify regular sound correspondences between two related languages# (the basis of the comparative method)# ------------------------------------------------------------------ ## Known cognate pairs: Latin → Spanish (simplified)
latin_spanish_cognates = [
# (Latin, Spanish, gloss)
('pater', 'padre', 'father'),
('mater', 'madre', 'mother'),
('uita', 'vida', 'life'),
('locus', 'lugar', 'place'),
('pluuia', 'lluvia', 'rain'),
('planta', 'planta', 'plant'),
('porta', 'puerta', 'door'),
('nox', 'noche', 'night'),
('luna', 'luna', 'moon'),
('terra', 'tierra', 'earth'),
('focus', 'fuego', 'fire/hearth'),
('filius', 'hijo', 'son'),
('filia', 'hija', 'daughter'),
('oculus', 'ojo', 'eye'),
('auris', 'oreja', 'ear'),
]
defalign_sequences(s1, s2):
"""
Simple global sequence alignment (Needleman-Wunsch, match=1, mismatch=-1, gap=-1).
Returns aligned sequences.
"""
m, n = len(s1), len(s2)
# Score matrix
score = np.zeros((m+1, n+1))
score[0, :] = np.arange(n+1) * -1
score[:, 0] = np.arange(m+1) * -1for i inrange(1, m+1):
for j inrange(1, n+1):
match = score[i-1,j-1] + (1if s1[i-1]==s2[j-1] else -1)
score[i,j] = max(match, score[i-1,j]-1, score[i,j-1]-1)
# Traceback
a1, a2 = [], []
i, j = m, n
while i > 0or j > 0:
if i > 0and j > 0and score[i,j] == score[i-1,j-1] + (1if s1[i-1]==s2[j-1] else -1):
a1.append(s1[i-1]); a2.append(s2[j-1]); i-=1; j-=1elif i > 0and score[i,j] == score[i-1,j]-1:
a1.append(s1[i-1]); a2.append('-'); i-=1else:
a1.append('-'); a2.append(s2[j-1]); j-=1returnlist(reversed(a1)), list(reversed(a2))
# Count correspondence pairs
correspondences = defaultdict(int)
for lat, spa, gloss in latin_spanish_cognates:
a1, a2 = align_sequences(list(lat), list(spa))
for c1, c2 inzip(a1, a2):
correspondences[(c1, c2)] += 1# Sort by frequency
corr_df = pd.DataFrame(
[(c1, c2, count) for (c1,c2), count insorted(correspondences.items(), key=lambda x: -x[1])],
columns=['Latin', 'Spanish', 'Count']
)
print("Sound Correspondences: Latin → Spanish (top 20)")
print(corr_df[corr_df['Latin'] != corr_df['Spanish']].head(20).to_string(index=False))
# Highlight regular correspondences (appear ≥3 times)
regular = corr_df[(corr_df['Count'] >= 3) & (corr_df['Latin'] != corr_df['Spanish'])]
print(f"\nRegular correspondences (n≥3):")
for _, row in regular.iterrows():
print(f" Latin /{row['Latin']}/ → Spanish /{row['Spanish']}/ ({row['Count']}× attested)")
Advanced Usage
Automated Cognate Detection with LingPy
# ------------------------------------------------------------------ ## Using LingPy's SCA (Sound Class Alignment) for cognate detection# ------------------------------------------------------------------ #try:
from lingpy import Wordlist, LexStat
import lingpy.compare.partial as partial
# Create a CLDF-compatible wordlist# (requires proper input format — see LingPy documentation)print("LingPy cognate detection:")
print(" 1. Load Wordlist: wl = Wordlist('my_data.tsv')")
print(" 2. Run LexStat: lex = LexStat(wl)")
print(" 3. Cluster cognates: lex.cluster(method='sca', threshold=0.45)")
print(" 4. Inspect cognate sets: lex.output('tsv', filename='results')")
except ImportError:
print("LingPy not installed. Install with: pip install lingpy")
print("Using manual implementations instead.")
Troubleshooting
LingPy import errors
pip install lingpy --upgrade
# On some systems:
pip install numpy scipy matplotlib pandas networkx
pip install lingpy
Alignment produces all-gap output
Cause: Sequences are in different encoding (Unicode vs. ASCII).
Fix: Normalize to Unicode NFD and split by character:
