Reconstructing how Neanderthals grew, based on an El Sidrón child

How did Neanderthals grow? Does modern man develop in the same way as Homo neanderthalensis did? How does the size of the brain affect the development of the body? A study led by the Spanish National Research Council (CSIC) researcher, Antonio Rosas, has studied the fossil remains of a Neanderthal child's skeleton in order to establish whether there are differences between the growth of Neanderthals and that of sapiens.

Neanderthal children may have grown up as slowly as modern humans 
[Credit: © S.Plailly, E.Daynes/LookatSciences]

According to the results of the article, which are published in Science, both species regulate their growth differently to adapt their energy consumption to their physical characteristics.

"Discerning the differences and similarities in growth patterns between Neanderthals and modern humans helps us better define our own history. Modern humans and Neanderthals emerged from a common recent ancestor, and this is manifested in a similar overall growth rate," explains CSIC researcher, Antonio Rosas, from Spain's National Natural Science Museum (MNCN). As fellow CSIC researcher Luis Ríos highlights, "Applying paediatric growth assessment methods, this Neanderthal child is no different to a modern-day child." The pattern of vertebral maturation and brain growth, as well as energy constraints during development, may have marked the anatomical shape of Neanderthals.

Neanderthals had a greater cranial capacity than today's humans. Neanderthal adults had an intracranial volume of 1,520 cubic centimetres, while that of modern adult man is 1,195 cubic centimetres. That of the Neanderthal child in the study had reached 1,330 cubic centimetres at the time of his death, in other words, 87.5% of the total reached at eight years of age. At that age, the development of a modern-day child's cranial capacity has already been fully completed.

"Developing a large brain involves significant energy expenditure and, consequently, this hinders the growth of other parts of the body. In sapiens, the development of the brain during childhood has a high energetic cost and, as a result, the development of the rest of the body slows down," Rosas explains.

Neanderthals and sapiens

The cost, in terms of energy, of anatomical growth of the modern brain is unusually high, especially during breastfeeding and during infancy, and this seems to require a slowing down of body growth. The growth and development of this juvenile Neanderthal matches the typical characteristics of human ontogeny, where there is a slow anatomical growth between weaning and puberty. This could compensate for the immense energy cost of developing such a large brain.

Skeleton of the Neanderthal boy recovered from the El Sidrón 
cave (Asturias, Spain) [Credit: Paleoanthropology Group 
MNCN-CSIC]

In fact, the skeleton and dentition of this Neanderthal present a physiology which is similar to that of a sapiens of the same age, except for the thorax area, which corresponds to a child between five and six years, in that it is less developed. "The growth of our Neanderthal child was not complete, probably due to energy saving," explains CSIC researcher Antonio Rosas.

The only divergent aspect in the growth of both species is the moment of maturation of the vertebral column. In all hominids, the cartilaginous joints of the middle thoracic vertebrae and the atlas are the last to fuse, but in this Neanderthal, fusion occurred about two years later than in modern humans.

"The delay of this fusion in the vertebral column may indicate that Neanderthals had a decoupling of certain aspects in the transition from infancy to the juvenile phase. Although the implications are unknown, this feature could be related to the characteristic enlarged shape of the Neanderthal torso, or slower brain growth," says Rosas.

The Neanderthal child

The protagonist of this study was 7.7 years old, weighed 26 kilos and measured 111 centimetres at the time of death. Although the genetic analyses failed to confirm the child's sex, the canine teeth and the sturdiness of the bones showed that it to be a male. 138 pieces, 30 of them teeth (including some milk teeth), and part of the skeleton- including some fragments of the skull from the individual- identified as El Sidrón J1, have recovered.

(Left to Right) Antonio García-Tabernero, Antonio Rosas and Luis Ríos beside the Neanderthal child's skeleton 
[Credit: Andrés Díaz-CSIC Communications Department]

The researchers have been able to establish that our protagonist was right-handed and was already performing adult tasks, such as using his teeth as a third hand to handle skins and plant fibres. In addition, they know who his mother was, and that the child protagonist of this investigation had a younger brother in the group. Furthermore, this child was found to have suffered from enamel hypoplasia when he was two or three years old. Hypoplasia (white spots on the teeth, especially visible in the upper incisors), occurs when the teeth have less enamel than normal, the cause usually being malnutrition or disease.

Discovered in 1994, the El Sidrón cave, located in Piloña (in Asturias, northern Spain) has provided the best collection of Neanderthals that exists on the Iberian Peninsula. The team has recovered the remains of 13 individuals from the cave. The group consisted of seven adults (four women and three men), three teenagers and three younger children.

Previous studies have been carried out by a multidisciplinary team led by the paleoanthropologist Antonio Rosas (CSIC's National Museum of Natural Sciences), the geneticist Carles Lalueza-Fox (Institute of Evolutionary Biology, run by CSIC and the Pompeu Fabra University) and by the archaeologist Marco de la Rasilla (University of Oviedo).

Source: Spanish National Research Council (CSIC) [September 22, 2017]

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Nothing but the tooth: What dental remains from Homo naledi can tell us

Anthropologists just love to sink their teeth into a good mystery, and some recent research from NC State and Vassar College has done just that – by looking at what dental development in Homo naledi fossils can tell us about this human relative and the evolution of our own species, Homo sapiens.

H. naledi teeth in mandible [Credit: Alice Harvey]

In 2013, paleoanthropologists discovered the fossilized remains of at least 15 individual hominins, or human relatives, within the Dinaledi chamber of the Rising Star cave system near Johannesburg, South Africa. The remains were from an entirely new species, dubbed Homo naledi by the researchers. Recently, these fossils were determined to be around 200,000 – 300,000 years old, meaning that H. naledi walked the earth at the same time as other hominins like Neanderthals and possibly the earliest members of H. sapiens.

Chris Walker, assistant professor of anatomy at NC State, and Zach Cofran, a biological anthropologist from Vassar College, were researchers on the original team that studied the H. naledi fossils. Recently the duo had the opportunity to examine the dental remains of the youngest members of H. naledi to see if this extinct species grew more like humans or our extinct relatives.

Humans are unique among primates in how long it takes us to fully develop from child to adult. Chimpanzees, our closest living relatives, develop a bit faster than we do. Tooth formation and eruption patterns – the rate and order in which baby and adult teeth grow and emerge – also differ between humans and chimps. Scientists surmise that this difference may be related to the differences in developmental timing between the two species. Most evidence to date has suggested that the human-like pattern emerged quite recently in our evolutionary history and that our extinct relatives were generally more like chimps than humans with respect to dental development.

Walker and Cofran used CT scans of the mandibles of two H. naledi youngsters – one an infant and one an older child – to determine how the species’ teeth formed and emerged. What they discovered was surprising.

“Overall, we found a mixture of human and chimp patterns, although the eruption sequences in particular were human-like,” Walker says. “Given that H. naledi was alive so recently, similarities to humans aren’t necessarily shocking. But given the numerous primitive anatomical features of H. naledi – including a small brain, which is suggestive of a relatively fast, more chimp-like developmental pace – our findings are somewhat unanticipated. Even Neanderthals, a group that is much more anatomically similar to modern humans than H. naledi, have a more primitive dental eruption sequence.”

The uniqueness of the finding may actually raise more questions than it answers regarding H. naledi, and it potentially affects how anthropologists gauge the development times and life histories of ancient hominin species.

“A prolonged period of growth and development is a defining feature of humans, but we don’t know when this trait evolved,” says Cofran. “We’ve relied on teeth to make inferences about growth and development in extinct species because they preserve well in fossil samples and dental maturation has previously been linked to aspects of life history. But this finding, with the similarities between modern humans and H. naledi, raises questions about the adaptive significance of tooth emergence sequences.”

Walker and first author Cofran published their findings in Biology Letters.

Author: Tracey Peake | Source: North Carolina State University [September 13, 2017]

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