Big brother has a lot to answer for

December 07, 1999

HERE'S something else boys can blame their older brothers for: a slightly skewed body shape. So say doctors in Ontario, who have shown that the more older brothers a man has, the more likely he is to show random asymmetries in his body shape, a sign of troubled development in the womb.

Martin Lalumire of the Centre for Addiction and Mental Health in Toronto and his colleagues studied 40 adult male psychiatric patients and 31 male hospital employees. They were asked about how many older and younger siblings they had, and whether they were brothers or sisters.

They also looked for random differences between one side of the body and the other. If our development in the womb were flawless, we would be perfectly symmetrical. The small asymmetries we have are thought to be the result of the problems faced by the developing fetus, such as a mild infection in the mother.

The team measured features such as finger lengths and ear size. Some variations between left and right were excluded because they may have a function. People are most often right-handed and seem to have more ridges on the right hand than the left, which possibly helps their grip.

But five asymmetries did seem to be random: hand and ear width, and the lengths of the ear, third and fifth finger. Having an older brother predisposed an individual to be less symmetrical. The more older brothers, the more marked the asymmetry was likely to be. Older sisters had no effect.

The researchers speculate that male fetuses trigger an immune reaction in their mothers. Genes on the Y chromosome, which is unique to males, produce an antigen called HY, and this may set off the mother's alarm bells. Each successive male would boost that response. This theory is backed indirectly by other studies. One showed that the placenta, which protects a fetus from the mother's immune system, increases in size with each successive male.

The good news is that brothers pose no risk to girls. "Even though mum's immune system is primed, there's nothing to respond to," says Lalumire.
-end-
Author: Alison Motluk, Toronto

Source: Proceedings of the Royal Society B (vol 266, p 2351)

PLEASE MENTION NEW SCIENTIST AS THE SOURCE OF THIS STORY AND, IF PUBLISHING ONLINE, PLEASE CARRY A HYPERLINK TO http://www.newscientist.com

UK CONTACT - Claire Bowles, New Scientist Press Office, London:
Tel: 44-0-20-7331-2751 or email claire.bowles@rbi.co.uk
US CONTACT - New Scientist Washington office:
Tel: 202-452-1178 or email newscidc@idt.net

New Scientist

Related Immune System Articles from Brightsurf:

How the immune system remembers viruses
For a person to acquire immunity to a disease, T cells must develop into memory cells after contact with the pathogen.

How does the immune system develop in the first days of life?
Researchers highlight the anti-inflammatory response taking place after birth and designed to shield the newborn from infection.

Memory training for the immune system
The immune system will memorize the pathogen after an infection and can therefore react promptly after reinfection with the same pathogen.

Immune system may have another job -- combatting depression
An inflammatory autoimmune response within the central nervous system similar to one linked to neurodegenerative diseases such as multiple sclerosis (MS) has also been found in the spinal fluid of healthy people, according to a new Yale-led study comparing immune system cells in the spinal fluid of MS patients and healthy subjects.

COVID-19: Immune system derails
Contrary to what has been generally assumed so far, a severe course of COVID-19 does not solely result in a strong immune reaction - rather, the immune response is caught in a continuous loop of activation and inhibition.

Immune cell steroids help tumours suppress the immune system, offering new drug targets
Tumours found to evade the immune system by telling immune cells to produce immunosuppressive steroids.

Immune system -- Knocked off balance
Instead of protecting us, the immune system can sometimes go awry, as in the case of autoimmune diseases and allergies.

Too much salt weakens the immune system
A high-salt diet is not only bad for one's blood pressure, but also for the immune system.

Parkinson's and the immune system
Mutations in the Parkin gene are a common cause of hereditary forms of Parkinson's disease.

How an immune system regulator shifts the balance of immune cells
Researchers have provided new insight on the role of cyclic AMP (cAMP) in regulating the immune response.

Read More: Immune System News and Immune System Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.