Leading Figures

Frans Plooij - International Research-institute on Infant Studies (IRIS)
The Netherlands

Frans Plooij

Just married in 1971, Hetty van de Rijt and Frans Plooij left for the Gombe National Park, Tanzania, East-Africa to study chimpanzees with Jane Goodall, after having completed their studies in Educational Psychology, Physical Anthropology and Behavioral Biology. They were trained in systematic, direct observation of animal behavior in the field, in the tradition of Nobel Laureate Niko Tinbergen…

When they returned to Europe to work in Robert Hinde’s Medical Research Council-unit on the Development and Integration of Behavior, University Sub-department of Animal Behavior in Madingley, Cambridge, England, they had to analyze reams of data. Out of this analysis emerged the notion of regression periods—difficult periods where the baby clings more closely to the mother. This confirmed research that others had found previously in 12 other primate species. The results of the data analysis also supported the idea that in the course of early ontogeny a hierarchical organization emerges in the central nervous system that underlies the behavioral development of the free-living chimpanzee babies and infants.

Discovering Perceptual Control Theory

It was only after they had analyzed their data and discerned a hierarchical organization that their friend and colleague Lex Cools, a neurobiologist, suggested that they compare their findings about the capabilities of infants at the different stages of development to the levels of perception spelled out by Hierarchical Perceptual Control Theory (PCT) developed by William T. Powers. PCT turned out to explain their findings very well.

Mothers and Babies

Once they had earned their Ph.D. degrees in Cambridge, England (Hetty) and Groningen, the Netherlands (Frans), they moved on to observe and film human mothers and infants in their home environment. These studies demonstrated clearly that human babies, too, go through difficult age-linked regression periods in a similar way. With each difficult period babies make a leap in their mental development. Each time another layer of perceptual control systems is superimposed onto the already existing, hierarchically organized layers of perceptual control systems.


"Oops, I am growing! For Managers - Jump through your mental blocks"

This new book, published in Dutch by Margreet Twijjnstra and Frans Plooij, explains PCT in detail and applies it to Management.

The Wonder Weeks

Based on their research, Hetty and Frans wrote the original Dutch version of The Wonder Weeks, published in 1992 and followed in subsequent years by German, French, Swedish, Italian, Danish, Spanish, English, Japanese, Russian and Korean editions. During the 1990s, their original research in The Netherlands was replicated and confirmed by other researchers in Spain, Britain and Sweden.

They designed a parental support and education program named Leaping hurdles (Hordenlopen in Dutch) that was based on the Wonder Weeks, and published a scientific evaluation study on this program in Dutch. The program proved to be highly effective. The Wonder Weeks is now making life easier for parents and is contributing to the healthy development of children all over the world.

Unfortunately, Hetty contracted a rare, tropical disease during their stay in Tanzania and following a long, brave battle with the disease, she passed away in 2003.

Further Reading

Videos explaining Frans Plooij's work are available online here.

Check out the Wonder Weeks Website as it develops! Look for more background information, parent experiences and information on how to get in touch with other parents to share experiences.

Readers who want to know more about the scientific literature behind the book The Wonder Weeks may consult the literature listed below:

Plooij, F. (1984). The behavioral development of free-living chimpanzee babies and infants. Norwood, N.J.: Ablex.
Plooij, F. X. (2003). The trilogy of mind. En M. Heimann (Ed.), Regression periods in human infancy (pp. 185-205). Mahwah, NJ: Erlbaum.
Plooij, F., van de Rijt-Plooij, H. H. C., van der Stelt, J. M., van Es, B., & Helmers, R. (2003). Illness-peaks during infancy and regression periods. In M. Heimann (Ed.), Regression periods in human infancy (pp. 81-95). Mahwah, NJ: Erlbaum.
Plooij, F. X., van de Rijt-Plooij, H., & Helmers, R. (2003). Multimodal distribution of SIDS and regression periods. In M. Heimann (Ed.), Regression periods in human infancy (pp. 97-106). Mahwah, NJ: Erlbaum.
van de Rijt-Plooij, H., & Plooij, F. (1987). Growing independence, confl ict and learning in mother- infant relations in free-ranging chimpanzees. Behaviour, 101, 1-86.
van de Rijt-Plooij, H., & Plooij, F. (1988). Mother-infant relations, confl ict, stress and illness among free-ranging chimpanzees.  Developmental Medicine and Child Neurology, 30, 306-315.
van de Rijt-Plooij, H., & Plooij, F. (1992). Infantile regressions: Disorganization and the onset of transition periods.  Journal of Reproductive and Infant Psychology, 10, 129-149.
van de Rijt-Plooij, H., & Plooij, F. (1993). Distinct periods of mother-infant confl ict in normal development: Sources of progress and germs of pathology. Journal of Child Psychology and Psychiatry, 34, 229-245.