Kathy, I am being perfectly fair to GF. She is talking rubbish.
I know that research very well - and it does not give evidence for what GF is saying, and I have had to explain this several times to people who think it does.
Harris is contrasting weaning onto a variety of foods with weaning onto a restricted number of foods.
She is not saying 'wean at four months' at all.
She is not contrasting weaning at four months with weaning at 6 months.
The babies in her study were weaned at four months - that's just the age they happened to be.
If she repeated her study with babies at 6 mths, she might well find the ones who were least fussy were the ones who were weaned onto a variety of tastes.
It's a study of behaviour (she is a psychologist, not a nutritionist) and what she found is unsurprising in the extreme to anyone who knows anything about infant behaviour - make a fuss about weaning (at whatever age it starts) by restricting tastes and recording amounts and all the rest of the unnecessary paraphernalia about weaning we see all the time, and you are more likely to have a fussy baby.
Stay relaxed, follow your baby's lead and encourage a variety of tastes from the beginning, and your baby is less likely to be fussy.
Like, duh :)
This is nothing to do with weaning at 6 mths.