Why do babies have the Moro reflex, and why do some babies have it stronger than others?

The Moro reflex is present in all new-borns up to about 4-5 months in age. It is normally a response to a sudden loss of support (they feel like they’re going to be dropped). The baby will momentarily flail their arms out and cry (“Whoa! What happened!”) It is believed to be one of the only unlearned fears.

An Austrian paediatrician called Ernst Moro was the first to observe and put a name to the reflex. It is believed to be a feature of a new-born’s behaviour that has been passed down through evolution. If you watch the video clip (above) it is easy to appreciate that it must feel as if their support is breaking or moving from beneath them. There are other ways to prompt the reflex like blowing on the face, poking the abdomen or extending the legs – all seemingly cruel things to do.

No one is completely sure why babies have the Moro reflex but it seems to be an inbuilt reaction for a baby to try to regain a loss of support – the baby attempts to free its arms, then catch hold of its carer and cry to draw attention to its plight. As for the strength of the reflex, one of the most obvious questions is to ask if whether you are observing it in babies of a similar age. It is considered unusual for human babies to show the Moro reflex beyond about 5 months of age –  at which point other self-defence behaviours take over. As the baby grows, it is reasonable to expect the reflex to gradually erode in strength rather than be suppressed instantly. But, as with most things, there is always some variation between people. The reason you’re different to other people can usually be blamed on your parents (their genes, or otherwise!)

Answer by Lewis Pike and Matt Powell

Question from Hannah Tucker via Facebook

Article by Lewis Pike

August 15, 2013

Lewis studied BioMedical Sciences at Liverpool John Moores University and got a PhD in Microbiology and Immunology at University of York. He now spends more time helping people understand science writing than he should and wishing his colleagues would write more clearly for the public as well as each other.


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