It didn't necessarily work out like that for my kids. My daughter (middle child) is the A personality, high academic/career achiever (working towards doctorate so she can become a professor when she retires; currently a high muckety muck in one of the large international companies). My first son is also a type A personality, high career achiever, upholding the status quo (has only a GED; currently a high muckety muck in another large international company; slated to become a VP within a few years). My youngest son was the smoker, unconventional, challenger of the status quo. He also ignored boundaries, both moral and legal, and will be in prison for the next 20 years. Both my sons are atheist and my daughter claims to be a christian.

Seems to fit my life.

I'm a middle child, so took the part of a clown who kept all the siblings happy and working together. Unlike my older brothers and younger sister, I didn't take life seriously, and spent most of my life playing as much as I could, only doing work I enjoyed.

I'm 65 now and still doing that.

I was the last of 4 with the biggest gap and number 3 seams to be completly right

I was the younger of two children, and by far the highest academic achiever. My sister has always been more likely to uphold the status quo.I did smoke, rebel, take risks, and challenge the status quo. So, 2 of the 3 conclusions are confirmed in my case.

I've been fascinated by this phenomenon ever since studying birth order with Phil Zimbardo at NYU in the '60s. I was very close to Phil and was going to gradutae school to study social psych but got drafted and had to curtail my education.
Here's the concept: When a couple gets married the young mother is very responsive to the needs of the infant. It's a new challenge to her, you might say. So a phenomenon simillar to "Imprinting" in ducks occurs. If there's a safety pin sticking the baby or if he/she is hungry, they cry out and reief soon comes. The imprinting is so strong that the baby will go on to choose profession with close contact to others: psychiatrists, for instance, also nurses, doctors and teachers—they are "people persons" and reach out to others. The imprinting association stays with them their entire life, just as a duckling will follow its mother even if she's taken away then comes back years later.
Now, if the young mother isn't so young anymore, she's already raised a few kids, she's chatting on the phone and the baby starts crying, she says to herself, "Ah let it cry, I'll only be a few more minutes" (to take care of him/er). So this baby has to learn to take care of anxiety and pain independently. The association with other humans doesn't form. That's why we see the symptoms of #3 above. They choose jobs like bookkeepers, pilots, over-the-road truck drivers where they don't have to rely on others.

I suspect , as older siblings , the parents are more closely following , " the rules ," the first time around . Suceeding children , have less exclusive parental time , due to not being the only child , and the parents relax the rules , they held the oldest to . Most certainly , the older children are given some responsibility for the care of the younger children , but without any of the control methods , the parents are allowed to use . I recall , when I graduated from high school , a friend suggested that the two of us take a day trip to the ocean . I was not allowed to go . When my brother was in high school , our parents had moved to an island . He was given his own motor bike , money for gas and cigaretts , and often spent the night on the beach , encouraged by our father to , " find girls ," . End result , he failed his senior year , and had to take it over again .

I may be one that "falls through the cracks" on this. I was the last born of 3 or 4, I was told I had a Brother who died (not sure it was true), but I never knew I had a Sister and Brother still alive until my in my late 30s.

I have never smoked, and am not a needless risk taker. I will take a risks if there is a good reason. I am all in for challenging the status quo, but nearly every one is now thanks to our (USA) political nightmare.

I'm a first-born. I agree with point #1. Completely disagree with points 2&3.
I am FAR more unconventional than either of my siblings, and have taken a much
different life path. They are both parents, I am not. They're both married, I am not.
My youngest sibling is a youth pastor, and both are republicans.
Adam Grant never studied my family.

What about "only" children, such as myself?