Partly based on a study from the mutineers from the Bounty,
all people on earth will eventually have the same last name.
 

Do male babies may need more nurturing?

A woman's expectation of how long she will live appears to affect whether she has sons or daughters.  Dr Sarah Johns, a lecturer in biological anthropology at Kent University, found optimistic women are more likely to have boys.  Dr Johns quizzed 609 women who had recently become mothers.  She found that for every extra year a woman thought she was going to live, the odds of her first-born being a boy increased significantly.

Previous research has found that women in good physical health, and those who have comfortable living conditions have a tendency to give birth to boys.  Conversely, women living in harsh conditions tend to produce more girls.

Among the questions Dr Johns put to the new mothers was how long they expected to live.  Some of the women, who were mostly from lower-middle class and working class backgrounds, believed they would die as young as 40, while others believed they would still be alive at 130.  Dr Johns believes that an optimistic frame of mind may lead to physical changes in the body that make it more likely that a woman will conceive a male child.  For instance, it may alter the level of sex hormones around the time of conception.

She told BBC Radio 4's Today programme it was important that a boy's mother was not only in good physical condition, but that she had a positive outlook and the dynamism required to give him the best possible start in life.  By and large, there was a fair chance that a daughter would go on to have children of her own, she said, but for a male, the odds were much more variable.  The chances of a son going to reproduce were dependent on whether he actually made it to adulthood at all, and on whether, once adult, he had sufficient qualities to make him an attractive proposition.  She said: "It is much more difficult to raise a son to adulthood.  Male fœtuses put much more strain on the mother's body, they are more difficult to give birth to, and they are much more likely to take risks.  If you cannot invest in your son, making sure that he grows up to be successful and attractive to the opposite sex then it is likely he will not reproduce at all."

Dr Peter Bowen-Simpkins, of the Royal College of Obstetricians and Gynæcologists, said it was quite possible that the sex of a baby was decided by factors other than pure chance.  He said: "A lot more boys were born after the huge slaughter of men in the First World War.  "Somehow nature seemed to make up for what was lost."

The research is reported in the journal Biology Letters.

Source: news.bbc.co.uk Wednesday 4 August 2004

Nature Tracks the Scent of an Egg

Unreleased egg.  The cells surrounding the egg are important in ways not completely understood.
Source: news.bbc.co.uk/2/hi/health/4083371.stm

Sperm don't have noses, but according to a study by Loren Walensky of Johns Hopkins University, they do have chemical receptors that are structurally similar to those that noses use for smelling.  Researchers suspect the receptors sense the egg's "perfume" and guide the sperm to a rendezvous.

Although it was known that sperm track chemical signals from the, egg, scientists reporting to the annual meeting of the American Society of Cell Biology say they are surprised they do it with a receptor akin to one that normally functions as part of a complex nervous system.  Researchers earlier learned that sperm will swim toward follicular fluid, the liquid that bathes the egg when it is released from the ovary into a fallopian tube.  In other experiments, biologists have found that if sperm enter a fallopian tube when no egg is present, they become quiet and attach themselves to the tube wall.  Upon ovulation, the sperm start swimming towards the egg.

Walensky said the receptors are on the sperm's midpiece, a region just behind the head and packed with mitochondria, the organelles that produce the energy the tail needs to lash.  Although it seems likely that when a signal molecule from the egg binds to a receptor it activates swimming, it is not clear how this could cause sperm to swim in a particular direction. - Washington Post

Source: The Evening Post (Wellington) 31 January 1996

The Sperm-Egg Summit

Many sperm bind to the zona pellucida of a single unfertilised egg,
with the sperm tails giving the egg a fuzzy appearance.  Sperm do not
bind to fertilised eggs that have divided to produce two cells (arrowheads).

Source: Science volume 239 4 March 1988 photo P Wasserman of the Roche Institute of Molecular Biology in Nutley, New Jersey

Go Forth and Multiply

Sperm competing to fertilize an egg

Cells reproduce themselves in two different ways.  Most cellular reproduction is straightforward.  Once a cell grows to a certain size, it divides in two.  At the same time, each of the chromosomes in its nucleus (there are 46 of these in people) divides in two as well, ensuring that each daughter cell has a full set of genes.  Chromosomes are able to divide this way because the complementary nature of the strands in a DNA double helix allows the molecule to split down the middle and rebuild itself.

Chromosomes spend most of their time tangled together in the nucleus in a way which is not yet understood, but when a cell is preparing to divide, they unscramble themselves and can be seen separately with a suitably powerful microscope.  Protein threads pull each half-chromosome to one or the other end of the cell.  A waist then forms around the middle of the cell and gradually pinches it in two.

Sex cells (eggs and sperm in animals) form in a slightly different way.  Each of the chromosomes in a normal cell is actually one of a pair.  One member of the pair has come from the father, the other from the mother.  When a normal cell is about to divide into sex cells, the pairs first team up and swap some of their DNA, so that each cell contains genes from both parents.  The cell then divides twice in succession, but in the first division, the chromosomes do not themselves split.  Instead, one member of each pair goes to each daughter cell.

A sex cell, therefore, has half the usual number of chromosomes.  When a sperm fertilises an egg, their chromosomes are pooled and the normal number thus restored.

Source: The Economist 25 December 1993 - 7 January 1994

Unmatched Sperm
Chema Madoz Source: haha.nu/creative/creative-photos-by-chema-madoz

For more information on the curious DNA swap that sex cells perform, see also:

Genetic Conflict and Catharsis (further along in this section) - "...just before eggs and sperms are made in meiosis, every pair of chromosomes exchanges some of their genes.  This has an effect rather like prison warders constantly moving prisoners around to break up gangs.  It means that the Mark is often taken from Cain's chromosome and plonked down on Abel's chromosome...."

For more articles related to Men including sperm donations on the net, the effects of testosterone, condom sizes, buddies, smells, nagging, gynæcologists, mid-life crises, fathers and more click the "Up" button below to take you to the Table of Contents page for this section.