Why is it that some milestones are very time bound and others aren't?

[Northernbeachbum]

Firstly, this is not meant to be a goady question

Why is it that certain milestones such as solid foods at 6 months and even length of pregnancy are so strictly adhered to whereas things like walking no one questions a 9 month old walking or a 14 month old not?

Im guessing it's because things like sitting up if they happen late doesn't matter too much and delaying a baby ready for proper food doesn't matter but feeding one not ready too soon does?

Things like pregnancy dates must be based on a normal distribution curve?! So some people must be designed for longer pregnancies maybe?

Any ideas?

I'm presuming it's due to evidence about consequences? I.e. Plenty of evidence for the negative consequences of say, a gestation of 28 weeks vs. 40 weeks, but little evidence of consequences of walking at 9 months vs. 14 months. Also, we have some control over gestation, and complete control over when to start weaning, whereas for milestones such as walking it's completely baby led.

The milestones you're talking about happen earlier, so they're closer together as babies change much more quickly the younger they are.

There is some variance - a five week window for pregnancy due date, a 2-3 month window for solids readiness.

And it's because we know enough to do something about it.

Solid foods is an adult decision.
Walking is not!

no one questions a 9 month old walking or a 14 month old not?

That's not true, believe me! People fret over things like when they sit-walk-talk. My school friend tried to walk at 9m; her mother thought it was too early & knocked the child over to discourage it Child didn't confidently walk again until 14m.. :(. My step sis was OBSESSIVE when her son wasn't walking yet at 14-15 months and started consulting private paediatricians. People even get competitive about these milestones. And don't get me started on competition linked to when they start reading.

The idea of length pregnancy does differ per country but is it based on preventing of still births.

For miles stones there is a range of normal and babies don’t always do things in the right order. My DD was crawling months before she was sitting independently.

Full term is considered to be between 37 to 41 weeks so there is a range of normal there too.

Some milestones are recognised so being a vital part of normal physical and neurological development, and some aren’t. Sitting up, for example, is actually an important one. Doctors are worried if a baby can’t sit unaided by about 7 months as that would indicate problems with their muscles, coordination etc which might indicate an underlying condition. Similarly, a baby not socially smiling by 10 weeks or so might have an underlying condition. However, some milestones are not linked to normal development in the same way as not all babies do them - rolling and crawling are two examples. Plenty of neurologically typical babies never crawl; they always smile, turn to look for sounds etc by a certain age.