Environment can lead to a skewed male to female ratio
environment can influence the ratio of males to females in plants as well as in human beings, say studies done by two different teams of scientists. In case of plants, it is an aspect of demography balancing the population. For us, it is an environmental effect whose cause can be traced back to our activities.
It has been seen that when women are exposed to high levels of environmental pollutants called pcbs (polychlorinated biphenyls), they tend to give birth to more female children.
A study done on the serum specimens collected from pregnant women of the San Francisco Bay area in the 1960s showed that exposure to high levels of pcb decreased the chances of their bearing males by 33 per cent. pcbs are a class of chemical compounds used in industries as cooling and insulating fluids for electrical equipments and in varnishes. These contaminants accumulate in meat, fish and both animal and human breast milk. Having a strong affinity for lipids, the body tends to absorb and retain them in the system.
The study, which has been published in Environmental Health, found that for every one microgramme of pcb per litre of serum, the chance of having a male child reduced by 7 per cent. The researchers feel that the study will answer problems faced by populations living near toxic dumping grounds and effluent-contaminated lakes. It also gives an insight into other compounds structurally similar to pcbs, like the pbdes (polybrominated diphenyl ethers), used in plastic products, and the similar kind of health hazard that they can turn out to be.
In another case of environmental influence, scientists of the University of Canada have found that when the female species of dioecious or unisexual plants are in closer proximity to male species of the same plant, the females tend to receive more pollen and produce more female seeds.
The study was conducted on a wind-pollinated herb (Rumex nivalis) found in the Swiss Alps using genetic markers (known as dna sequences) to identify the sex of seeds.
The study mapped out the distance between the male and the female flowers of the herb in a common garden and came to the above conclusion. It also noted that in an environment where male flowers were fewer, more male seeds were generated. This helped balance the male scarcity.
The research concluded that the demographic aspects of the environment could promote selective fertilization by inducing the female-determining pollen tube to outgrow the male-determining pollen tube and fertilize the single ovule in each flower producing female seeds.