Neanderthal child with Down syndrome reveals ancient caregiving practices

By Vijay Kumar MalesuReviewed by Susha Cheriyedath, M.Sc.Jul 1 2024

In a recent study published in the journal Science Advances, a group of researchers in Spain investigated the caregiving practices of Neanderthals by examining a Neanderthal child with both Down syndrome (a genetic disorder caused by the presence of an extra chromosome 21) and congenital ear pathology (an ear disorder present at birth that affects hearing or balance) highlighting the group's role in providing extended care.

Background 

Caregiving for sick or injured Neanderthals has long been recognized, and there is increasing interest in its implications. Some researchers suggest caregiving arose from a complex social context with adaptive value. Further research is needed to understand the extent and nature of caregiving behaviors and their implications for social dynamics among Neanderthals.

Original fossil and 3D model of CN-46700. (A to D) original fossil. (E to H) 3D model. [(A) and (E)] anterior view. [(B) and (F)] Lateral view. [(C) and (G)] Posterior view. [(D) and (H)] Medial view. Scale bar, 5 mm.

About the study 

The taxonomic analysis utilized discriminant function analysis with data on variables Sagittal Labyrinthine Index (SLI), Anterior Semicircular Canal Radius (ASC-R), Lateral Semicircular Canal Radius (LSC-R), and Posterior Semicircular Canal Radius (PSC-R) from 29 Neanderthals, 23 fossil Homo sapiens (H. sapiens), and 26 modern humans. Cochlear variables, such as the number of turns (NT) and %L3 viz., the proportional length of the third cochlear turn, were taken from 10 Spanish and 20 British medieval specimens. The analysis was performed using International Business Machines Corporation Statistical Package for the Social Sciences version 29 (IBM SPSS v.29) was used for analysis. Pathological analysis compared CN-46700's diagnostic variables with Neanderthal samples from France (La Chapelle-aux-Saints, La Quina, La Ferrassie) and Israel (Amud, Kebara).

La Chapelle-aux-Saints 1, an adult skull, was dated using Electron Spin Resonance (ESR) (47 ± 3 ka) and thermoluminescence (56 ± 4 ka). La Quina H5, an adult calvarium, was dated between 63 and 40 ka. La Ferrassie 1 and 2, adult male and female skulls, were dated to 39.7 ± 2.3 ka. Amud 1, an adult skull, was dated to 53 ± 8 ka, and Kebara 1, an infant skull, to 60 ± 6 ka.

Micro-computed tomography (μCT) scanning of CN-46700 (the identifier for a specific Neanderthal fossil specimen from the Cova Negra site) was performed at the Museo Nacional de Ciencias Naturales, Madrid, using a Computed Tomography Scanner Model XT H-160 (CT-SCAN-XT H-160) scanner, producing 1535 slices. Mimics software was used for virtual reconstruction.

Measurements on the three-dimensional (3D) model of CN-46700 followed existing protocols and newly developed ones. The SLI, NT, and third turn lengths were measured. Age at death was estimated using the petromastoid canal method. New protocols measured the bony island's area, diameter, and lumen cross-sectional areas. Vestibular Aqueduct (VA) measurements followed the Cincinnati protocol. Cochlea volume and nerve canal width were measured using established protocols.

Study results 

μCT scans of the original fossil were used to reconstruct a 3D model for measurement and analysis. Six taxonomically relevant inner ear characteristics were utilized to differentiate Neanderthals from H. sapiens, including the placement and radii of the semicircular canals (SLI, ASC-R, PSC-R, and LSC-R) and two cochlear variables (NT and %L3). Despite CN-46700 having an abnormally reduced cochlear volume, correlation analysis showed that cochlear volume does not affect NT and %L3 values.

The SLI value for CN-46700 aligns with the Neanderthal mean but deviates significantly from modern humans and H. sapiens fossils. The NT and %L3 values also fall within Neanderthal variability but are outside modern H. sapiens ranges. Discriminant function analysis with semicircular canal variables on a sample of Neanderthals, fossil H. sapiens, and extant H. sapiens assigned CN-46700 to Neanderthals with 94% probability, justifying its classification as H. neanderthalensis.

The obliteration of the subarcuate fossa and the presence of a petromastoid canal in CN-46700 suggests age at death of over 6 years, aligning with growth rates similar to modern human children. The petromastoid canal's dimensions support this age estimate, indicating overall growth parallels between Neanderthals and modern humans.

Pathological evidence shows CN-46700 has LSC dysplasia (a congenital abnormality in the development of the LSC), indicated by an anomalous dilatation of the LSC and reduced dimensions of the bony island. The anterior semicircular canal also exhibits a hypoplastic bony island, while the PSC remains normal. The presence of an enlarged vestibular aqueduct (EVA) and a small fistula between the PSC and the VA further corroborates the pathological assessment.

LSC dysplasia, common in modern humans, often accompanies inner ear malformations such as EVA, leading to severe sensorineural hearing loss and vestibular symptoms like vertigo and imbalance. The cochlear volume in CN-46700 is significantly smaller than the Neanderthal sample average, although it does not exhibit Mondini malformation. The vestibule is also reduced in size, unlike typical vestibule enlargements seen with LSC dysplasia.

Conclusions 

To summarize, the diverse malformations in CN-46700 suggest a syndrome compatible with LSC dysplasia and EVA, most likely Down syndrome, given the exclusion of other syndromes. Down syndrome entails impairments in growth, cognitive development, and motor skills, requiring significant care. The survival of CN-46700 to at least 6 years indicates continuous, extensive caregiving, likely involving group assistance. This case highlights the social structure of Neanderthals, supporting vulnerable members unable to reciprocate care. It supports the theory that Neanderthals practiced caregiving and collaborative parenting, reflecting a complex social adaptation similar to that of modern humans with ancient evolutionary roots.