Scientists find a microscopic mating choice among human eggs

Human eggs might be using some cryptic chemical-based selection to choose the male gamete most suitable for mating, a study found.

In some cases, the chemoattractants released by the female egg might reject their actual partner’s gamete or sperm, causing infertility without a physical cause.

Infertility affects both men and women, with one in every six people worldwide experiencing it in their lifetime, said the World Health Organisation (WHO).

Most cases of infertility are caused by physical or mental limitations in either of the mating partners. However, some cases remain unexplained.

The study highlights a microscopic cause of infertility which could have been affecting partners for years.

Infertility and causes

Infertility is a common reproductive problem where mating partners are not able to conceive a child despite many attempts.

As per a report, the possible causes of infertility among men are alcohol consumption, poor sperm count, penile dysfunction or deformity, chronic ailments and other conditions.

For women, there could be structural problems with the fallopian tubes, lack of ovulation, uterine deformities, hormonal conditions like PCOS and other issues.

In most cases, either of the mating partner or both have some limitations preventing fertilisation or in sustaining a pregnancy.

However, for some, the causes are not known yet.

Cryptic female choice in mating

A study conducted by the Stockholm university in collaboration with Manchester university found that female eggs use some chemicals to attract the most suitable sperm, favouring one over the others. 

The human egg is surrounded by follicular fluid which secretes some chemoattractants when sperms approach the egg for mating.

Scientists found this follicular fluid from one female was better at attracting sperms from one male and the same fluid from another female was attracting a sperm from another man, showing a microscopic choice involved in mating which in some cases could be different from a social choice of a partner.

The study stated that this remote form of chemical communication which happens between an egg and a sperm before mating has been an observed cause to increase sperm density around the unfertilised egg.