Men and women are two biological entities. It has chemistry.Thus another subject of bio-chemistry. This is how both the sexes are differentiated.   Chemical bonds in both the sexes lead to their psychological structure; Social atmosphere tries to accommodate them. Due to biological differences there are differences of cultural views and approaches at them too. Religion also calculates them differently.  In the field of ethics here is a question of equality among them or equity but they are not uniform.

Sex is the basic for every species of the earth. Species including human being are organisms divided into two specialized categories male and female, two genetic traits.   

Known as gametes cells. Male species have XY chromosomes and females hv XX. Now wot is chromosomes. This is well constructed DNA and RNA protein. These two are containing genes. Every living being depends on genetic material and their all activities depend on it. This is their RNA chains.Regulation of gene expression determines wotll u think or act upon. Who u r is because of the transcriptional initiation of DNA.   

Your body structure, your brain neurons, your attitude, your hunger, common hereditary diseases all depends on genes, SO SEX IS THERE. It is molecular genetics. So you are a person of gene product. All i said is sex. Sex is not actually coitus or what we say F...k. That is just one kind of mating.
But in our society when we pronounce the word sex our attention goes at the area in between the legs. That is moronic idea of uneducated people around. But when you are a biologist then the word sex is not wot general people mean. The way i talk and behave even now while I am talking is a kind of Transcription factor. 

When you go to fill up any form have u noticed you need to feel up the question of your sex as male or female? So sex is not only wot u think in general and surely when a poet writes, a scientist researches or an Imam preaches his or her heritability is his/her molecular genetics.   
When you hear a nice voice of a Muazzin and nice recitation of Quran by a man it is so distinct due to his epigenetic, DNA sequence. 

In biology XY chromosomes and XX have their own characters and they are always trying to meet somehow and this is not the sexuality wot we common people think about. Those who have XX also tries to get appeased by XY.It works in your brain in the amygdale. Very shuttle and very distinct There is some behavioral traits known as biology, genetics, epigenetic, ethology,psychology, complex chemistry