Darwin therefore suggested sexual selection stating that any characteristic that benefits reproductive success will become the norm over time as it is consistently selected. Sexual selection involves inter and intra sexual selection. Intra sexual selection is the evolutionary process in which members of one sex (usually males) compete with each other for members of the opposite sex. Those who win are able to pass on their genes, which include the factors that made the winning person successful. This helps to ensure the offspring’s survival whilst passing on successful genes.
For fertilization to take place, sperm must be present either a couple of days prior to or on the day of ovulation. Sperm must first cross the barrier of the cervix, which will be thin and watery if the woman has just ovulated. Once the sperm have traversed the cervical mucus, they travel up the moist lining of the uterus into the Fallopian tubes. Since only one of the Fallopian tubes contains an egg, many sperm travel in the wrong direction. Fewer than 1,000 sperm out of the millions in the semen reach the Fallopian tubes, and only a few dozen actually reach the membrane of the egg.
The eyes are almost fully developed. Also the baby has developed most of he/she organs and tissues, reaching the weight of ½ to an ounce in the third month (12 weeks). When reaching the fourth month (16 weeks) will be very exciting for the parents because the sex is identifiable. The baby is developing reflexes, such as sucking
A part of the blastocyst will become the placenta, which will serve to nurture the growing embryo. Another section of the blastocyst will contain the inner cell mass that makes up the embryo. The cells of the inner cell mass are the embryonic stem cells, which can give rise to all the types of cells found in an adult human body. Embryonic stem cells can form around two hundred and ten
The baby can respond to sound and their heart will beat faster if a light is shined on the mother’s abdomen. The baby now has hair, eyelashes and eyebrows, as well as a strong grip and kick. By months 6 to 9, the baby can suck their thumb and will be more active when the mother lies down. How the mother feels affects the fetal activity. There is plenty of room in the womb so the baby can move around.
“This begins to stimulate the development of glands in male’s testes that release the hormone testosterone and in female’s ovaries that release a form of estrogen called estradiol (Tanner, 1990), the so-called sex hormones. Those researching the field of biopsychology have developed medications to assist individuals suffering from hormonal or chemical imbalances in being able to
In the first 3 months of prenatal development, all individuals start out the same, however after 3 months if the individual is male, then male sex hormones such as testosterone are produced from the testes which begin the development of male genitalia. The role of hormones on genitalia development can be seen by studying intersex individuals – those who have been exposed prenatally to abnormal hormone levels. When a genetically male embryo is exposed to too little male hormones, the newborn may appear to be externally female; known as Androgen Insensitivity Syndrome (AIS). Imperato McGinley studied a family of four boys in the Dominican Republic which this syndrome. The four boys had female external genitalia and were brought up as girls, but once they reached puberty, the sudden rise of male hormones had made them develop male external genitalia.
Steroids consist of cholesterol which comes from placentas in the womb. They can also derive from the adrenal gland or gonads that are testes or ovaries. Steroids play a huge part of the determination of the physical development of individual from the early ages in life to when we age and in all fertility cycles. Peptides control such functions as sleep, and distribution of sugar. Psychologists have not been able to determine the extent to which biological causes may affect the gender of an individual, but the evidence is expanding in which biological factors may explain, and offer an insight of the lifelong mystery of the formation of gender.
Infants born with a deficiency of thyroxine must receive it at once or they will be mentally retarded. Once the most rapid period of the brain’s development is complete children with too little thyroxine grow at a below-average rate but the central nervous system is no longer affected. With prompt treatment, such children cat up in body growth and eventually reach normal size. The most important hormone that the pituitary gland produces is the growth hormone (GH) which is necessary for development of all body tissues except the central nervous system and the genitals. Children who lack GH reach an average mature height of only 4 feet, 4 inches.
The first stage of the male brain is what Louann calls “The Boy Brain”. From the point of conception there are noticeable distinctions between male and female brains. From an early age “The genes that turn on will trigger the urge to track and chase moving objects, hit targets, test his own strength, and play at fighting off enemies” (Brizendine, 10). It is a biological impulse for boys to be action-oriented. Two hormones dominate a boy’s fetal development, testosterone and MIS or Müllerian inhibiting substance.