Universiteit Leiden

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Research project

Breastfeeding and Weaning in the Past and Present

Implications for health, demography & social-cognition.

2016 - 2021
Andrea Waters
ERC Starting Grant ERC Starting Grant

Breastfeeding is an evocative subject, the source of many opinions and debates. Brought to bear on the subject are social, cultural and religious viewpoints often contrasted with medical, nutritional and psychological viewpoints. Often lacking is a perspective that considers the process of breastfeeding and weaning in an evolutionary framework, looking into our deep temporal past and incorporating broad geographic, cross-cultural knowledge. This is the unique contribution of anthropological and archaeological research and what this research project will bring.     

Breastfeeding and weaning

By weaning we mean the period of time beginning when non-breastmilk foods are first introduced and the consumption of breastmilk ceases. Non-breastmilk foods are usually introduced no later than six months of age as by then the rapidly growing infant needs additional sources of nutrition. The cessation of breastfeeding however is much more variable. Ethnographic research of recent populations, historical information, and archaeological research on prehistoric populations has found it occurs anywhere from as early as one year to as late as six years of age with a mean age of weaning cessation of around 3 years.

Important behaviour

Breastfeeding and weaning are very important behaviours to have knowledge about because, firstly, they have a strong effect on infant health and survival, and hence the health and survival of a population.

Especially important to a population’s size is the average number of children born per woman and the amount of time that elapses between consecutive births, called the inter-birth interval. Breastfeeding, particularly if suckling is frequent, reduces female fecundity and hence longer periods of breastfeeding can lead to a longer inter-birth interval and fewer children born per woman. Thus, secondly, breastfeeding is an important factor in the demographic composition of a population, influencing it’s propensity to grow or decline in size.

Thirdly, the demographic composition of a population is also important in the social-cognition of a group via differences in observational and experimental knowledge acquisition. 

This early stage of life is arguably the most important as it sets the stage for everything that comes after. Yet, it has seen insufficient research. 


The problem is that there are large lacunae in our knowledge about breastfeeding and weaning in past populations.  

  • We lack adequate temporal depth, only possessing data going back about 11,000 years which is a very small proportion of our evolution as bipedal apes.
  • In addition what data we do possess are based on quite small sample sizes.
  • We lack a complete understanding of the correlation between breastfeeding and weaning and physiological stress. The weaning process can be stressful but it doesn’t have to be, and in fact oftentimes it is not.   
  • And finally, there has been no research exploring if there are social-cognitive learning differences in populations with different infant feeding patterns causing different demographic compositions.

4 objectives

This research project has 4 objectives.

  1. The development of a method that overcomes the limitations of our currently employed methods for the reconstruction of breastfeeding and weaning from the skeletal and dental remains of past peoples. This method is synchrotron-based x-ray fluorescence of strontium to calcium ratios in dental enamel.
  2. The application of this new method to three different past populations with different subsistence practices and thus possibly different infant feeding patterns.  Of particular importance is the assessment of the role of animal milks as a weaning food.

  3. The investigation of the correlation between different weaning parameters and physiological stress, in both modern and past populations. The parameters being the total length of breastfeeding, the timing of different events, the velocity and amplitude of weaning, and the common types of weaning foods.

  4. A meta-analysis about the relationship between a population’s demographic structure and aspects of social cognition, in particular observational and experimental knowledge acquisition.

A naturally shed 'baby tooth' used for dental analysis.


This project’s impact, at the broadest-level, is that by pushing the frontiers of our knowledge about breastfeeding and weaning in past and present populations my team and I will tap into the adaptational underpinnings of our species, useful in better understanding what is best for us in this day and age, and in demonstrating the importance of infant feeding data for understanding how we, as a species, have come to be the way we are.

Both the past and the present are needed to fully understand each other.

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