The purpose of sexuality is reproduction. There are non sexual reproduction methods can be identified among simple beings and as well as within the world of plants.
However when the evolution of beings becomes advanced, Sexual reproduction method has promoted well and it became the dominate feature. As a result of transforming beings towards a progressive path, the world of creatures appeared. The world of creatures is superior to the world of plants. Dominate feature of the sexuality of plants is hermaphroditism. But within the world of creatures, unisexual creatures are the dominate group. And the reproduction method also limited only to sexual reproduction within the world of creatures.
In the primary stages of evolution, the method of reproduction is simplex even though it is sexual reproduction. Male and female sex differentiation was also simple and that was only for generate the gametes. Most of simple beings were aquatic. Fertilization between simple male and female gametes occurred. When the creatures become evolutionally advance, the sexuality become advance too. The reproductive organs and tissue became complex. Growing the embryo inside a womb is the most advanced feature of reproduction. External genitals which can be well recognized were appeared. External genitals and the internal reproductive organs are pre determining by the sex chromosomes, so the genetic sex determination has taken the priority. Biochemical functions such as actions of sex hormones are also important in sex determination.
One group of sex, either male or female is dominating the whole species of creatures. The capability of interact with the natural environment more actively is the fact of determining that. Dominating of male creatures is the most recognized feature. Female domination is rare and it is not evolutionally advanced. Mammals are the most advanced creatures in evolution. At last human beings are evolutionally superior to all other creatures. Human sexuality is more advance and it is complex too. Most outstanding feature of human sexuality is the psychological factor and this is known as gender. Physical and genetic factors of sex are common for both human beings and other creatures. If we considered about the hominid evolution, there can be identified a special path of psychological transformation. Human beings created cultural environments and civilized due to this reason. In any culture, gender specifications are conspicuous. Human beings are wearing clothes and this feature is unique to human beings. In any culture there are specific male clothes and specific female clothes. Gender specific human activities can be identified within any culture and they are common. Finally all of these specifications are for better attraction between two sexes. Matching up male sex drive and the female sex drive is an important and essential part of any civilization. Advanced gender specifications are advanced in evolution too.