Natalie, do not worry about your brother. He will come back to you when he's older. Your mum is right, people have to go through these changes.

And of all the big changes that occur between birth and death, few are in the control of the ever-changing person. We make choices - what subjects to concentrate on, what job to get, whom to marry etc - but these choices do not change our lives as fundamentally as the stuff that just happens, the stuff that comes the way of any human animal, if he or she lives long enough.

Looking around, you might think that the biggest change that a human can undergo is to turn from a middle-aged woman into an old woman, as old women often seem like they come from another planet entirely. Old men, on the other hand, seem like middle-aged men, only older.

Or perhaps the change from boy to man, as your brother is suffering from, that  might seem the greatest change, greater perhaps than the change from girl to woman? (Women would probably disagree.) Or is the change from gurgling, burbling bundle of babyness to walking, talking miniature adult the biggest change?

Well, actually, no. The biggest change a human can experience in the normal course of events is to become a parent. To start with, your sense of time is altered from the outset. As the baby develops in the womb, you know from your own experience that this will be, for the child-to-come, a time of pre-history, a time without full reality, and so it seems to you at the time.

Then the baby is born and you are so involved in its life that your sense of time adjusts to fit baby-time which, is of course, much huger than grown-up time - a year in the life of a two-year-old is half a lifetime, after all.

Also, obviously, you can’t help becoming less selfish and more aware of what matters. You stop flirting with extravagant, unworkable schemes. You are constantly knackered. And you’re probably getting more knackered anyway, as a result of getting older, and so you’re even knackereder. You’re poorer too, but that’s OK because you’re less selfish.

When you do get a chance to socialise, you flabbergast yourself by spending the whole time telling tedious (fascinating to you) tales about your miraculous child. You develop a whole new set of instincts and reflexes. You send thank you letters as if from the child when the child is only two even though you know that that is absolutely excruciating whenever someone else does it.

All in all, unless you do the dirty and scarper from the scene altogether (an option more likely to be taken by men) once you have had a child, life will never be the same again. The funny thing is - not long after having one child, most people seem to want to have another one.