Everything alive descends from things that reproduced, and from nothing else

Question: Why do we exist?
Position1 of 3›: We exist to procreate
Argument‹2 of 2: Everything alive descends from things that reproduced, and from nothing else

The argument

A second argument offered for this position is a filtering argument. Of all the living things that have ever existed, proponents note, only those that left descendants have any descendants, which is a triviality until one sees what it implies. Every feature of every organism now alive has come through a filter that passed on only what was compatible with reproducing. Nothing else could have survived the passage. Whatever else we are, we are the output of a process that selected for exactly one thing. The argument is that this makes the reproductive answer not merely one explanation among several but the only one that could have been true of us. A purpose can be ascribed to a thing from outside, but a process that has shaped something continuously for as long as it has existed has a stronger claim on the word. On this reading, asking what we are for is like asking what a riverbed is for: the answer is given by what made it, and the shape is the record of the making. Holders of the position accept that this leaves the question feeling unanswered for many people, and they argue that the feeling is informative rather than a defect in the account. We are equipped with a strong drive to find intentions behind events, which is useful when the events are caused by other people and misleading when they are not. The expectation that existence must be for something, they argue, is itself a product of the same filter, and recognising where that expectation comes from is a better outcome than satisfying it with an answer the evidence does not support.

Premises

[P1]Every living thing now existing descends only from ancestors that successfully reproduced, so every inherited feature has passed through that filter. [P2] A process that has continuously shaped something for the whole of its history has the strongest claim to say what that thing exists for. [P3] The expectation that existence must have an intention behind it is itself an inherited disposition to look for intentions. [C] The reproductive account is the only account of why we exist that our own history supports.

Counter-arguments

Opponents reply that the argument establishes a constraint rather than a purpose. That only reproducers have descendants explains why we have the features we have, but a filter is not an aim, and nothing that merely filters can be said to intend anything. They also argue that the final move is self defeating: if our disposition to seek intentions is discredited by its origin, so is our disposition to accept evolutionary explanations, which has the same kind of origin. Several add that human beings pursue many ends that the filter did not select, and do so deliberately.

Rejecting the premises

[Rejecting P2] Shaping is not intending, and the argument needs the stronger notion to answer a question about why we exist rather than about how we came to be as we are. [Rejecting P3] Explaining where a disposition came from does not show that what it reaches for is absent, and the same move would discredit the reasoning used to make it. [Rejecting C] A constraint on what could have survived is compatible with there being a purpose as well, so the account does not establish that it is the only one available.