During the first two years of human life a common neural substrate underlies the hierarchical organization of elements in the development of speech as well as the capacity to combine objects manually, including tool use. Subsequent cortical differentiation, beginning at age two, creates distinct, relatively modularized capacities for linguistic grammar and more complex combination of objects. An evolutionary homologue of the neural substrate for language production and manual action is hypothesized to have provided a foundation for the evolution of language (...) before the divergence of the hominids and the great apes. Support comes from the discovery of a Broca's area homologue and related neural circuits in contemporary primates. In addition, chimpanzees have an identical constraint on hierarchical complexity in both tool use and symbol combination. Their performance matches that of the two-year-old child who has not yet developed the neural circuits for complex grammar and complex manual combination of objects. (shrink)

Is there something distinctive about humanity that justifies the idea that humans have moral status while non-humans do not? Providing an answer to this question has become increasingly important among philosophers as well as those outside of philosophy who are interested in our treatment of non-human animals. For some, answering this question will enable us to better understand the nature of human beings and the proper scope of our moral obligations. Some argue that there is an answer that can distinguish (...) humans from the rest of the natural world. Many of those who accept this answer are interested in justifying certain human practices towards non-humans—practices that cause pain, discomfort, suffering, and death. This latter group expects that in answering the question in a particular way, humans will be justified in granting moral consideration to other humans that is neither required nor justified when considering non-human animals. In contrast to this view, an increasing number of philosophers have argued that while humans are different in a variety of ways from each other and other animals, these differences do not provide a philosophical defense for denying non-human animals moral consideration. What the basis of moral consideration is and what it amounts to has been the source of much disagreement. (shrink)