Why do we have baby teeth?

Baby teeth, also known as milk teeth or deciduous teeth, start forming in the jaws of a baby in utero with the front teeth almost fully formed (apart from the roots) by the time of birth. Baby teeth erupt from about 6 months starting with the front teeth and are usually all present by the age of two and a half years. The first permanent grinding tooth (molar) erupts just behind the last baby molar. Then the front baby teeth get slowly replaced with permanent teeth and by about 12 years of age all the permanent teeth are erupted in the mouth and by adulthood most people have their 3rd molars (“wisdom teeth”).

The jaws of infants and children are far too small to accommodate the larger permanent teeth. Baby teeth are essential for the development of the mouth. They maintain the jaw length, and provide guides for the eruption pathway and therefore proper placement of permanent teeth.

Humans aren’t the only species who have two sets of teeth, but not all animals who have teeth have two sets. Some animals, such as hamsters and moles, only have one set of teeth in their lifetime. Most other vertebrates such as reptiles and fishes have the ability to replace their teeth over and over again. The tooth sizes are very similar and non-specialsed.

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So, really, the question is why do we only have one set of baby teeth and permanent teeth!

Mammals have very specialised sets of teeth that need to fit together properly to work well. Each tooth has a specific function and they need to work together as a unit, which makes chewing much more efficient for the purposes of getting nutrients from food. If they are constantly being shed and replaced throughout life the precision matching of shape and size of neighbouring teeth that enable that efficient chewing is lost.

But there is a trade off with developing such specialised teeth – it takes more energy to make them, so we are left with one set of teeth during development and one throughout our whole adulthood.

 

First sighting of a wild newborn chimpanzee taken from mother and cannibalised.

The first ever witnessed case of a newborn wild chimpanzee being taken from the mother and subsequently eaten was published by researchers from Japan this week in the American Journal of Anthropology. The authors explain that this most likely occurred because the pregnant chimpanzee did not go on “maternity leave”, a period near the time of birth that the mother chimpanzee hides and gives birth alone.

Just a matter of seconds after the mother, Devota, gave birth and before she could touch her newborn, an adult male chimpanzee, Darwin, picked up the infant and took it into the bush. The researchers therefore couldn’t confirm if it was a live or still birth or the sex of the infant. Darwin and other members of the group were subsequently seen eating the newborn. At the time of the incident in 2014, there were about 60 members in the group, with 20 adult females and 10 adult males.

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There have been 45 sightings of infanticide in wild chimpanzee groups in six different populations, but never around the time of birth. This incident occurred in group “M” from the Mahale Mountains National Park in Tanzania, which have been studied since 1968. The authors found clear evidence for maternity leave from data from their daily attendance records between 1990 and 2010 with a total of 94 births to 36 females.

Infanticide perpetrated by males has been observed in many primate species and is usually explained as being a male reproductive strategy, whereby males increase their chance of fathering an infant by killing unrelated infants, and results in the mothers becoming fertile again sooner after birth.

The authors propose explanations for why Devota gave birth without “maternity leave”: 1) the baby was preterm and was therefore “not expected”; 2) it was her first pregnancy and had not learned the behaviour of “maternity leave”; and 3) she felt safe in the group as she may have copulated with a number of males around the time of conception of the infant.

Stressed-out mums and demanding children: understanding the maternal – infant interface at the beginnings of agriculture

Modern society is rooted in a dependency on agriculture. Although this is often thought to be a positive human development, the transition to agriculture-based societies had substantial negative impacts on human health, many of which continue to affect millions of people today. The bulk of these negative impacts are borne by the most vulnerable in society – mothers and children.

Recent research in the Arica region in the Atacama Desert in Northern Chile is giving us new insight into how the roots of this transition to agriculture in prehistory affected human society, in particular mothers and their infants. Our research collaboration between the University of Otago in New Zealand, the University of Tarapacá Chile, and Durham University in England is using a multidisciplinary approach to reveal a picture of stresses associated with food shortages, and their possible connections to premature death and vitamin deficiencies in newborn babies.

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The Atacama Desert is well-known for the earliest evidence in the world for deliberate mummification of the dead, predating Egyptian mummies by more than two millennia. The intricate funerary rituals associated with the pre-agricultural Chinchorro people of this area were largely focused on infants and children. This has led some to hypothesise that it was a social response to high rates of foetal, infant and maternal death in these populations. Historically, archaeological research in the Atacama has focused on these pre-agricultural mummies, but recent research has highlighted periods of increasing infant mortality later in prehistory – during the transition to agriculture. The ultimate causes of this increase in stress, however, have eluded archaeologists.

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The project took a two-pronged approach to this problem, studying changes to diet using chemical signatures in bones and teeth, and assessing their health impacts by looking for signs of pathology on the skeletons of early agricultural populations. Published recently in the International Journal of Paleopathology, and covered here, an Early Formative Period site just transitioning to agriculture (3,600-3,200 years before present) showed that all the infants have evidence of scurvy (nutritional vitamin C deficiency). Interestingly, so did an adult female found buried with her probable unborn child. First author Anne Marie Snoddy says “In addition to contributing to knowledge of the interplay between environment, diet, and health in the Ancient Atacama, this paper provides the first direct evidence of potential maternal-foetal transference of a nutritional deficiency in an archaeological sample”.

This study also used new methods for analysing diet and stress using the chemistry of bones and teeth, these also reveal a picture of early-life stress recently published in the American Journal of Physical Anthropology and covered by Forbes.  “The preservation of mummies in the Atacama gives us an unprecedented opportunity to use tooth chemistry to look at prehistoric infant experience. We have chemical evidence of stress from tissues which form even before the infant is born, showing how the mother’s health is impacting her baby” says author Charlotte King. This work contributes to an understanding of the sensitive relationship between the health of the mother and infant in the past, including the maternal-infant transference of stress signals and micronutrient deficiencies.

 

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Anne Marie Snoddy doing her palaeopathological analyses in the Museo Universidad de Tarapacá San Miguel de Azapa, Arica, Chile.

 

The research is giving new insight into human adaptation to one of the harshest environments in the world. The Atacama Desert experiences less than 2 mm per year of rainfall, making agricultural resources very vulnerable. However, the marine environment is remarkably rich, owing to the upwelling of the cold Humboldt ocean current, resulting in an abundance of marine mammals and fish. Chemical analysis is showing that the people of the desert buffered themselves against the vulnerability of their agricultural resources by continued reliance on these marine foods. Even so, periodic food shortages from El-Niño events in the area were likely, and the skeletal evidence for vitamin C deficiency is interpreted as being related to these events.

A version of this story was originally published here.

 

 

 

‘Oh baby’ – new things to come for The Bioarchaeology of Childhood

2017 was a busy year for me, but I am excited that this blog is continuing to receive good readership and positive feedback. This year I have resolved to communicate new research in the broader biological anthropology field to a wider audience through more frequent posts and new content.

So why should we care about babies and kids in anthropology?

The start of life is the most critical time for humans. From the susceptible prenatal period, the hazards of childbirth, to seemingly harmless bugs that can’t be fought off by infants’ underdeveloped immune systems; their lives are fragile.

Although human babies are born in an extreme state of helplessness compared with all other primates, through millions of years of evolution there has been a development of ways to support infants and children during this critical time. Consider, for instance, the miraculous rooting reflex to find their mother’s nipple in an otherwise utterly helpless newborn, the interaction of babies’ saliva and breastmilk to fight germs, and the development of advanced social cooperative care for the young.

Anthropological reconstructions of the world were once devoid of children altogether, in line with social perception at the time that children should be seen and not heard. What we now know is that children are integral to understanding most facets of human life today and in the past. For example, early illnesses are now known to have later-life health consequences not only within our own lifetimes, but also for our children and grandchildren. Also, just as the World Health Organisation uses child mortality and growth as sensitive measures of population wellbeing, this can give us invaluable insights into living conditions in past communities. Past child mortuary practices are also central to unlocking the social identity of the young and those related to them, and therefore the wider social tapestry.

This blog will communicate the latest childhood biological anthropology, archaeology, and forensic anthropology research to a wide general audience. Future posts will share stories on coffin birth, how women’s pelvic bones adapt during their lifetime to aid in reproduction, midwifery in our hominin past, past childcare practices, and much more.

Here are three of the most read pieces from 2017:

Why were so many babies murdered in the past?

The late mediaeval agrarian crisis and the Black Death revealed through stressed childhoods

Having babies as an academic archaeologist

Thank you for your support and all the best for 2018!

 

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