There are various authors who, within the realm of bioethics, propose as a model of the human being, a man who is enhanced, transhuman or even posthuman. The philosophical roots of these bioethical thinkers have not been sufficiently analysed. In this article our aim is to demonstrate the connection of this movement with the evolution of philosophy over the past several decades. Therefore, and keeping in mind that the transhumanist-posthumanist proposals appeared in the last decades of the 20th century, a time when important philosophical change was afoot, with a movement from the modern age to the postmodern, we begin our article by identifying the philosophical characteristics of both periods, as well as the relationship that exists between them. We will analyse synthetically the conception of the human being, of ethics and of empirical science in both periods, coming to the conclusion that the postmodern era is the result of the radicalization of ideas that were already latent in modernity. Afterwards, and following a brief summary of the postulates of transhumanism-posthumanism, we study the links that this current of thought has with modern and postmodern perspectives regarding the human person, ethics and technoscientific activity. We conclude that even though transhumanist-posthumanist thought has roots in modernity, its objectives and their theoretical bases reveal a strong dependence on postmodern thought. And further, since this latter current of thought is, at base, antihumanist it is logical that transhumanism-posthumanism, influenced by postmodernity, would reveal a strong tendency not merely to negate what the human being is, but even to forget what it is out of a desire to construct something different from the human in the future.