Fertility is the ability of people or animals to produce healthy offspring in abundance. In the English language, the term was originally applied only to females, but increasingly is applied to males as well, as common understanding of reproductive mechanisms increases and the importance of the male role is better known. The opposite of fertility is infertility.

Human fertility depends on factors of nutrition, sexual behavior, culture, instinct, endocrinology, timing, economics, way of life, and emotions. Animal fertility is no less complex, and may display astounding mechanisms.

Fertility is also applied to farmlands and plants, where it implies a capacity to yield large crops of sound fruits, seeds or vegetables.

The fertility rate is a demographic measure of the number of children per woman. Although it has been until recently considered to be a fairly reliable indicator of population growth, it is no longer so in much of Asia. Due to selective abortion and other factors, the number of women themselves is declining. Therefore, the fertility rate as it has traditionally been defined is no longer an authoritative measure of population growth in China, India, and Myanmar.

Both women and men have hormonal cycles which determine both when a woman can achieve pregnancy and when a man is most fertile. The female cycle is approximately twenty-eight days long, but the male cycle is variable.

Women ovulate at about the fourteenth day of their cycle, this obviously being the most fertile time for females.

Men can ejaculate and produce sperm at any time of the month, but their libido dips occasionally, which scientists guess is in relation to their internal cycle.

During the fourteenth week of fetal growth, a womenšs eggs (or ova) form in her ovaries, where they will remain until puberty.

At puberty, the eggs will eventually start to mature one-by-one. At ovulation, the egg bursts from the ovary sometimes causing a small, sharp pain called mittelschmerz. If the egg is not fertilized by the malešs sperm, the egg will break down within twenty-four hours into its components (mostly protein) and be reabsorbed by the body.

Fertility

Research breakthrough on male infertility   PhysOrg - May 13, 2011
Around one in 20 men is infertile, but despite the best efforts of scientists, in many cases the underlying causes of infertility have remained a mystery. New findings by a team of Australian and Swedish researchers, however, will go a long way towards explaining this mystery.

Scientists discover human sperm gene is 600 million years old   PhysOrg - July 16, 2010
Sperm in All Animals Originated 600 Million Years Ago   Live Science - July 16, 2010

Why do certain diseases go into remission during pregnancy?   PhysOrg - June 17, 2010

Why do certain diseases go into remission during pregnancy?   PhysOrg - June 17, 2010

More than just the baby blues   PhysOrg - June 16, 2010
Within the first week after giving birth, up to 70 percent of all women experience symptoms of the baby blues.

New Test Reveals Good vs. Bad Sperm   Live Science - June 1, 2010

New Hormone Treatment Shows Potential to Reverse Infertility   Science Daily - March 16, 2010

Women lose 90 per cent of 'eggs' by 30   Telegraph.co.uk - January 27, 2010

Sperm Prefer Attractive Females   Live Science - July 9, 2009

  Scientists claim sperm 'first'   BBC - July 8, 2009

Secret Birth Control Method: The Welcome Dance of the Uterus   Live Science - March 8, 2009

5 Myths of Fertility Treatments   Live Science - March 5, 2009

5 Myths of Fertility Treatments   Live Science - March 3, 2009

Moment of ovulation captured on video Telegraph.co.uk - June 12, 2008
These are the clearest pictures ever taken of what is the starting point of every human life: ovulation occurring inside a woman's body.

New technique opens fertility treatment to thousands of women Guardian - July 2, 2007

First baby from lab-matured egg BBC - July 2, 2007

Key to Male Infertility Found Live Science - July 1, 2007

Babies reach out in the womb News in Science - February 5, 2007

New IVF technique triples success rate Guardian - February 1, 2007

Parents Pick Sex of Child in New Clinical Trial Live Science - October 27, 2005

Fertility Study Looks At Ovulation's Intricate Working Science Daily - June 22, 2005

Scientists are developing artificial wombs, sperm and eggs Guardian - May 19, 2005

Parents 'could pick babies' sex' BBC - March 2005

4-D Ultrasound Gives Video View of Life in the Womb National Geographic - February 2005

Eggs 'fertilized' without sperm BBC - December 2004

'Ovary-arm' transplant a success BBC - November 2004
A woman undergoing cancer treatment has had her fertility saved after doctors transplanted her ovary into her arm.

Scans uncover secrets of the womb BBC - June 2004

A new type of ultrasound scan has produced the first vivid pictures of a 12 week-old fetus "walking" in the womb.

Mice created without fathers BBC - April 2004

Scientists have created two female mice without fertilizing the eggs they grew from.

'Virgin birth' mammal rewrites rules of biology New Scientist - April 2004
A mammal that is the daughter of two female parents has been created for the first time.