In the sixth edition Darwin inserted a new chapter VII (renumbering the subsequent chapters) to respond to criticisms of earlier editions, including the objection that many features of organisms were not adaptive and could not have been produced by natural selection. He said some such features could have been by-products of adaptive changes to other features, and that often features seemed non-adaptive because their function was unknown, as shown by his book on Fertilisation of Orchids that explained how their elaborate structures facilitated pollination by insects. Much of the chapter responds to George Jackson Mivart's criticisms, including his claim that features such as baleen filters in whales, flatfish with both eyes on one side and the camouflage of stick insects could not have evolved through natural selection because intermediate stages would not have been adaptive. Darwin proposed scenarios for the incremental evolution of each feature.
Why did Darwin introduce a new chapter in On the Origin of Species in the sixth edition?
to respond to criticisms of earlier editions

During adolescence, the human body undergoes various physical, physiological and immunological changes triggered and mediated by hormones, of which the most significant in females is 17-β-oestradiol (an oestrogen) and, in males, is testosterone. Oestradiol usually begins to act around the age of 10 and testosterone some months later. There is evidence that these steroids act directly not only on the primary and secondary sexual characteristics but also have an effect on the development and regulation of the immune system, including an increased risk in developing pubescent and post-pubescent autoimmunity. There is also some evidence that cell surface receptors on B cells and macrophages may detect sex hormones in the system.
Which specific hormone precipitates the change in immunology in males?
testosterone

Accurate present day child labour information is difficult to obtain because of disagreements between data sources as to what constitutes child labour. In some countries, government policy contributes to this difficulty. For example, the overall extent of child labour in China is unclear due to the government categorizing child labour data as “highly secret”. China has enacted regulations to prevent child labour; still, the practice of child labour is reported to be a persistent problem within China, generally in agriculture and low-skill service sectors as well as small workshops and manufacturing enterprises.
In 2014, the U.S. Department of Labor issued a List of Goods Produced by Child Labor or Forced Labor where China was attributed 12 goods the majority of which were produced by both underage children and indentured labourers. The report listed electronics, garments, toys and coal among other goods.
Chinese children have been known to make electronics, toys and what else?
garments