根据以下资料，回答题：
        The story that traces life from sea to land then into the multiple niches that exist there for a great variety ofliving things is a fascinating one, but far too detailed for our purposes．One key point for us in that story is theemergence of the biological class of animals that are called mammals．
        Mammals have a number of features that distinguish them from the reptiles from which they developed．Theyare warm-blo0ded; that is, they have a system of temperature control that keeps the body at a constant temperature．Mammals have a set of teeth of different shapes that serve different functions such as cutting, gouging, andgrinding．Young mammals spend their earliest days of development shielded within the mother's body and are thenborn alive, rather than hatching from eggs．In addition, after bi~h they are nourished by milk provided by themother's mammary glands．The enforced association between mother and infant provides an opportunity ．forlearning that does not exist for those kinds of creatures that are hatched from eggs long after their parents havedeparted from the scene．Young mammals play---something that amphibians and reptiles never do--whichprovides additional learning opportunities．
        The foregoing list leaves little doubt that we are mammals．There are, of course, a great many kinds ofmammals, most of which developed after the great extinction of dinosaurs and other reptiles about 65 million yearsago that opened opportunities for the few small mammals that were already in existence．One of the groups ofmarmmals that resulted was a biological order called primates which includes monkeys, apes, humans, and somesmaller creatures familiar only to ardent zoo goers．Primates share a number of behavioral features that have playedimportant roles in their evolutionary development．Most primates are arboreal; that is, they spend their lives in andamong trees．Their tree-climbing and tree-dwelling habits impose needs that are reflected in primate anatomy．Although diet varies from species to species, many primates are largely vegetarian．But they can eat and digestmeat, and some species vary their diets of leaves, shoots, and fruits by eating insects, birds' eggs, and even smallanimals．Primates are hand-feeders, depending on their hands both to collect food and to get it into their mouths．Perhaps the most important feature of their behavior is that primates are social animals．Their genetics, habits, andeven their survival are geared to living in groups．Although human beings have come to have a way of life verydifferent from that of typical primates, the basic primate adaptation provided prehumans with capabilities thatallowed them to become culture-builders．
        The anatomical features that separate primates from other kinds of animals relate clearly to the way primates behave．

Where do you think is the passage from?