According to a well-known theory in evolutionary biology healthy females should give birth to more males than females. A study funded by the Swiss National Science Foundation shows why this is not always true.
According to popular belief, whether you have a baby girl or boy is purely a matter of chance. And yet, a study published several years ago shows that mothers in stressful jobs, for instance, give birth to more girls than boys.
The correlation between such shifts in the offspring sex ratio and the mother’s overall state is something that evolutionary biologists are familiar with from other animal species. One influential hypothesis puts natural selection as an explanation for the imbalances observed.
Strong males with high reproductive success
The Trivers-Willard hypothesis states that it is beneficial for mothers to be able to adjust the sex of their offspring in response to their own state of health. Accordingly, a female in good condition should give birth to more male offspring.
This is because successful males have the potential to produce more children in their lifetime than successful females. By producing strong sons, healthy mothers increase the probability of their own genes being widely distributed. Conversely, low-ranking females who are not in such good shape are more likely to produce daughters, because the chances of giving birth to a future dominant male are poor.
“However, it’s not quite as simple as that,” points out biologist Peter Neuhaus sponsored by the Swiss National Science Foundation, based at the University of Calgary in Canada. Taking the example of a model with data from Columbian ground squirrels and Canadian bighorn sheep, Neuhaus – together with colleagues from the UK, the US, France and South Africa – has demonstrated in an article published in Nature magazine that optimal reproduction also depends on a series of other factors.
Dead before reaching sexual maturity
Bighorn ewes, for instance, give birth to only one lamb a year. Most females mate with the dominant ram, which means many of the other males don’t get a chance. Females in a good state often pass on their condition and so can be expected to “to make supermales”, as Neuhaus explains.
Nonetheless, the healthy females do not produce more male than female offspring. As the model demonstrates, other parameters, such as the fact that a large number of males die before reaching sexual maturity, play a central role in assessing reproductive potential.
But what have sheep got to do with mothers in jobs with some degree of stress? Nobody doubts that they have more girls, but Neuhaus advises caution: “Evolution is very complex. To understand how it works, you need to take into account as many factors as possible that could influence reproductive potential.”
(*) S. Schindler, J.-M. Gaillard, A. Grüning, P. Neuhaus, L. W. Traill, S. Tuljapurkar & T. Coulson (2015). Sex-specific demography and generalisation of Trivers-Willard theory. Nature online: doi:10.1038/nature14968
(Available for journalists as a PDF file from the SNSF: email@example.com)
Prof. Peter Neuhaus
Department of Biological Sciences
University of Calgary
Calgary, AB, T2N 1N4, Canada
Tel.: +1 403 220 8776
Time difference: -8 hours
Dr. Susanne Schindler
Institut für Evolutionsbiologie und Umweltwissenschaften
Tel.: +41 76 295 36 85
Medien - Abteilung Kommunikation | idw - Informationsdienst Wissenschaft
Researchers identify potentially druggable mutant p53 proteins that promote cancer growth
09.12.2016 | Cold Spring Harbor Laboratory
Plant-based substance boosts eyelash growth
09.12.2016 | Fraunhofer-Institut für Angewandte Polymerforschung IAP
Physicists of the University of Würzburg have made an astonishing discovery in a specific type of topological insulators. The effect is due to the structure of the materials used. The researchers have now published their work in the journal Science.
Topological insulators are currently the hot topic in physics according to the newspaper Neue Zürcher Zeitung. Only a few weeks ago, their importance was...
In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.
Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...
Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
09.12.2016 | Life Sciences
09.12.2016 | Ecology, The Environment and Conservation
09.12.2016 | Health and Medicine