TomL's argument, and its derivatives, are a failure to identify A as A. That is, a failure to identify our nature.
It also seems many people here have also confused Objectivism (and generally, the domain of Philosophy) with categories of knowledge (obtained through the process of Reasoning) like Evolutionary Biology and Evolutionary Psychology. As such, a quick read through these subjects would clear up exactly what is a metaphysically absolute (e.g. our need to breath, need to reproduce and their resulting behaviour) and what is not.
Briefly, I will present the conclusions of those who've directed the exercise of their reasoning to gain a wealth of information about our nature as man (see the categories of knowledge mentioned above for more information):
we are vessels programmed to carry and propagate our genetic material into the next generation of vessels (i.e. survive and replicate)
we come 'hardwired' with certain gender-neutral and gender-specific values that aids the above
Examples of certain 'hardwired' gender-neutral values are oxygen, food and water (to sustain our survival) and sex with an opposite member of our species (to replicate).
And to aid replication, we have a further set of "hardwired" gender-specific values that indicate other values that would lead to successful replication. For example facial symmetry indirectly indicates the presence of genetic fitness (see Natural Selection and Sexual Selection) which leads to successful replication. Thus we've come to value facial symmetry.
By the same process but of gender-specific values: men have come to value youth, full lips, a specific waist-to-hip ratio; women have come to value musculature, height, a specific waist-to-shoulder ratio. Further, more so than a man's, women's gender-specific values also extend to behaviour: particular body language, wit, humour.
Whenever we perceive these attributes in a potential mate, our "hardwired" values are triggered, consequent emotions are evoked and bubble through to the realm of conscious thought as "I must f**k him/her". This is what we call "physical attraction", "physical beauty" or "physical attraction".
These responses are no more under our conscious control than our ability to control the functioning of our kidneys. To use objectivist philosophy, these are the metaphysically absolute and by extension are Objective -- we cannot choose not to need to eat or procreate.