Final answer:
The substance found in a typical wing feather and in human fingernails is keratin. Keratin is a primary structural protein that provides hardness to skin, hair, and nails, and is produced by cells known as keratinocytes.
Step-by-step explanation:
A typical wing feather consists of keratin, which is also found in human fingernails. Keratin is a tough, fibrous protein that gives skin, hair, and nails their hard, water-resistant properties. It is produced by cells known as keratinocytes, which are the most predominant type of cell found in the epidermis.
Nails are composed mainly of keratin, and they carry out several important functions. Firstly, they act as protective plates over the fingertips and toes, preventing injury. Secondly, they enhance sensation by acting as a counterforce to the sensitive fingertips, thereby aiding in the handling of objects. Nails can also be used as tools.
Similarly, hair is made of keratin and serves functions such as filtering particles and keeping the body warm. Besides mammals, no other animals have hair as it is a characteristic feature of this group.