Survival of a species depends upon environmental conditions that provide life-sustaining elements. Mammals also rely on maternal instincts, habits and behavior that produce offspring and maintain the species. Mammals are the true mothers of nature. One well-known characteristic that separates the class of mammals from other animals is the mammary glands. Found only in mammals, these glands produce milk or a milk-like liquid.
All mammals feed their young through the process of lactation.
Milk-producing creatures have noteworthy differences that divide them into more specific categories. Eutherian, or placental, is one infraclass of mammals. Eutherians define mothers with placentas, a special organ that plays an important role in nourishing the young before birth. Humans are placental along with most farm animals, a majority of domestic pets and some unusual wildlife. Compared to Eutherians in the wild here in Pennsylvania, humans have one of the longest gestation periods at around 266 days.