Someone please give reason for thymus gland's absence in a newly born child.

Thymus gland is large and more active in neonatal and infants and continues to grow throughout yhe childhood.During this phase, the thymus matures more than enough T- cells to last throughout the childs life , so at puberty it begins to decrease in size . Fat slowly replaces the thymus until it becomes quite small in older adults. In older people it degerates so they become ill easily.