The Science of Why Babies Cry More and What Parents Need to Know

You may have noticed that your baby sometimes seems calm and relaxed…and then goes through a ‘fussy’ phase, where they seem to cry no matter what you do. Do these fussy phases happen on a predictable schedule? Is it predictable for all babies…and for all parents? In this episode, we dive into the research behind the theory of the Wonder Weeks, as described in the books and app. This popular concept suggests that all babies experience predictable periods of fussiness in preparation for going through developmental ‘leaps,’ but the science behind it may be much more limited than you expect. We break down the available research, explain why babies might cry more at certain stages, and help parents understand the truth about these so-called Wonder Weeks.

What topics do we cover?

How Wonder Weeks became a popular theory
What actual research says about baby crying phases
Ways to support your baby during fussy times, whether or not Wonder Weeks apply

By the end, you’ll feel more informed about why babies cry and have a clearer idea of whether Wonder Weeks is a useful tool for understanding your baby’s needs.

If you’re expecting a baby or have a child under the age of one, you’re likely feeling a mix of excitement and overwhelm. The Right From The Start course is designed to give you the tools and confidence you need to navigate those early months with ease. Whether it’s sleep, feeding, play, or your baby’s development, this course offers evidence-based guidance that helps you understand your baby’s needs during key stages, including those fussy "Wonder Weeks" moments.

In the Right From The Start course, you’ll learn exactly how to support your baby during these challenging times, and how to create a secure, loving environment that nurtures their growth at every stage.

What you’ll get from Right From The Start:

Practical advice for sleep, feeding, and developmental milestones—especially during those Wonder Weeks!
Insights into how your baby’s brain develops, and what’s really going on during those early (and sometimes challenging) months.
Tools for managing routine activities like diapering, dressing, and communication, with strategies that align with your baby’s natural development.Beyond the knowledge, you’ll also gain access to a supportive community of parents who are navigating the same challenges, so you never have to feel alone.

Ready to get started? Click below to explore Right From The Start and prepare for a smoother, more empowered first year with your baby! Episodes Mentioned:

Books mentioned in this episode:

The Wonder Weeks by Dr. Frans Plooij and Hetty van de Rijt

Jump to Highlights: 00:03 Introduction to the Podcast and Wonder Weeks 02:19 Background on the Plooys and Their Research 05:43 Methodology and Findings of the Plooys' Study 10:20 Criticisms and Limitations of the Plooys' Study 20:11 Replication Studies and Their Findings 59:42 Conclusions and Implications References: Aldridge, J. Wayne, et al. "Neuronal coding of serial order: syntax of grooming in the neostriatum." Psychological Science 4.6 (1993): 391-395.

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Witters, D. (2020, September 1). 50% in U.S. fear bankruptcy due to major health event. Gallup. Retrieved from: https://news.gallup.com/poll/317948/fear-bankruptcy-due-major-healthevent.aspx#:~:text=Story%20Highlights&text=WASHINGTON%2C%20D.C.%20%2D%2D%20Half%20of,from%2052%25%20to%2064%25.&text=How%20concerned%20are%20you%20that,or%20not%20at%20all%20concerned&text=pct.,pts.&text=This%20study%20is%20based%20on,concern%20among%20women%20(51%25). [accordion] [accordion-item title="Click here to read the full transcript"] Denise 00:03 Denise, hi everyone. I am Denise, a longtime listener of your parenting Mojo. I love this podcast because it condenses all the scientific research on child development, compares it with anthropological studies, and puts it into context of how I can apply all of this to my daily parenting. Jen has a wealth of resources here, so if you're new to the podcast, I suggest you scroll through all her episodes. I'm sure you'll find one that will help you with whatever you're going through, or one that just piques your interest if you'd like to get new episodes in your inbox, along with a free infographic on 13 Reasons Your child isn't listening to you and what to do about each one. Sign up at your parenting mojo.com forward, slash, subscribe. Enjoy the show. Jen Lumanlan 00:58 Hello and welcome to the your parenting Mojo podcast. Have you seen the Wonder weeks book, or did you download the app? The book has apparently sold over 2 million copies, and the app has been downloaded over 4 million times. So, the approach has certainly struck a chord with parents. It seems to help that the book was developed by two PhDs, Dr Franz ploy and his wife, Hetty vanderai ploy, whom I will refer to together as the ploys. And I know that when I see PhD following the neighbor of an author, I perceive the author as having some credibility. They've now been joined by their daughter, Xavier plus ploy, as the CEO of the Wonder weeks. Apparently, Hetty actually died quite young in 2003 so when you hear me refer to Dr ploy. Later in the episode, is Dr Franz ploy. So, in this upcoming pair of episodes, I want to ask two overarching questions. In this first episode, we'll ask is the idea of Wonder weeks backed up by scientific research. And then in the upcoming episode, we'll ask, okay, based on what we learned here in the first episode, what if anything should we do with the ideas in the book to help us and our baby? So, if you're expecting or you have a child under the age of one, this episode is very much for you. Let's get started with our first question and look at the scientific research behind the Wonder. Weeks. So, Franz ploy studied biology and psychology. His wife, Hetty, studied educational psychology and anthropology, and together, they observed chimpanzees with Jane Goodall in Gombe National Park in Tanzania between 1971 and 1973. Jen Lumanlan 02:30 Franz obtained his PhD in the behavioral development of chimpanzee babies, and Hetty got hers in mother baby interaction in chimpanzees. Because these dissertations were submitted in the early 1980s and fortunately, I couldn't find any copies online, possibly as part of their dissertations or in related work. The employees noticed that baby chimpanzees seemed to go through a series of what they termed regression periods, by which they meant a return to behavior like clinging to their mother and nursing often which they hadn't done so much only a week or so previously. The ploys hypothesized that each of these regression periods was followed by a developmental leap, and they wondered whether similar periods might exist among human babies. Several previous researchers had generally coalesced around the idea that there are four major behavioral transitions in human babies. And in the late 1980s the ploys began a research project to see if these were all of the transitions, or if they could find any more. And they decided to do this by identifying periods of regressive behavior in babies, because there was agreement in the literature that these regressive periods accompanied developmental transitions. They say that this literature finds that some sort of transitions do exist, and that these occur at two, 712, and 18 to 21 months. Unfortunately, the literature here mostly consists of books rather than peer reviewed papers. It's not an exaggeration to say you can pretty much publish anything you want in a book. That's why we have the peer review process in journals, so other people look at papers before they're published and check that they are grounded in previous literature. It isn't a perfect process by any stretch of the imagination, but at least you know someone who knows the subject has checked it out. The ploys cite 13 authors or sets of authors in support of this claim, so I tried to track each of them down. Unfortunately, seven of them were book chapters or books themselves, and of course, these are books published in the 1970s and 80s, so I wasn't able to get a hold of them. One paper was a discussion about relationships between peer infants, which isn't...

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