Conception And Gender of Babies

The sexes

A definition of ‘sex’ in the biological sense is that it is the sum total of the differences that make up what we know as ‘maleness’ and ‘femaleness’. It is distinct from gender, which can best be described as the psychological (rather than anatomical) feeling of being either masculine or feminine, a man or a woman; it is gender that exerts a major influence on our personalities and sexual behaviour.

What determines our ‘biological’ sex is in essence our genetic make-up: someone who possesses two X-chromosomes is female; one X-chromosome and one Y-chromosome makes a male.

Although chromosomes carry the blueprint for our sexual make-up, the mediators which actually govern the differentiation of the early embryo into male or female in the uterus are the sex hormones. These belong to a group of chemical compounds known as steroids*. The sex hormones can be divided into two groups: the androgens or male sex hormones such as testosterone, and the female sex hormones, like oestrogens and progesterone.

Embryonic differentiation

Until a few weeks after conception, male and female embryos look identical. Even the tissues which will ultimately develop into testes in a boy baby, or ovaries in a girl, have the same appearance. The sex chromosomes soon begin to exert their influence, however, and the gonads (the principal sexual organs) start to differentiate. At the age of about six weeks, in an embryo with a Y-chromosome tiny tubes begin to appear in the gonads. Those tubules will eventually form the sperm-producing testes. In a female embryo, with two X-chromosomes, these tubules do not form, and the ovaries begin to develop. The primitive testes or ovaries in their turn promote the further development of the genitalia, under the influence of the sex hormones.

As already stated, both male and female sex organs stem from the same set of primordial organs in the embryo. In a developing boy, the genital protuberance forms into a penis, and the genital swellings on each side into a scrotum. In a girl the clitoris develops from the genital protuberance and the genital swellings become the labia. At birth these primary sexual characteristics help to determine the sex of a baby. After this short burst of activity at one of life’s earliest stages, the sex hormones exert almost no influence until puberty, the time when the reproductive organs become functional.