Questioning the Molecular Mother

Mother-Foetus relationship: Truly unselfish?

Years and years of glorification of the eternal love between mother and child has lead to hundreds of movies, books and whatnot. Is it true or is it exaggerated? On a molecular level, it isn’t all hugs and kisses between the mother and the growing foetus; rather, it is a competition for resources and survival. Shocking? The competition gets interesting as we delve deeper.


Source: Giphy


The Red Queen Hypothesis- an Arms Race in play

Imagine you’re running on a treadmill, which has no speed control. It suddenly switches to a higher speed and unless you run at that speed, you will fall on your face. So you move faster. The treadmill keeps varying its speed, and so do you, within seconds, for if you don’t, you will hurt yourself pretty badly. Now let’s see this through an evolutionary looking glass. A prey and a predator have to constantly evolve to counter each one’s defence or offense. Say a bacterium develops resistance to a particular antibiotic; unless humans develop another method to control or eliminate the pathogen, the bacteria will infect the host and flourish, maybe even killing the host in the process. This need for a constant evolution is referred to as the Red Queen Hypothesis, named after the character from ‘Alice in Wonderland’. A more general terminology used is ‘an arms race’, where neither the prey nor the predator wins, as they constantly evolve. We can observe this arms race between many permutations and combinations of prey-predator pairs, but what is interesting is that there exists an arms race between the human mother and foetus, amongst other mammals.

Why does this arms race exist if the mother’s genes are carried by the foetus?

This is why there exists a competition- the foetus only carries half of the mother’s genome and the other half is the father’s genome. This makes the mother question whether this foetus is worth her time and efforts. If you thought the endometrium was a pink comfortable cushion for the zygote to attach to, think again. Studies conducted on mice show that the endometrium is one of the most difficult places for the zygote to adhere to. So if you thought that bearing a child was the ultimate act of altruism, prepare to change your mind.

The father’s genes desperately need the foetus to survive, because what is the guarantee that the mother will have another baby with him again? This is how gene imprinting gives the foetus an advantage. Certain genes from the father’s genome help the foetus to implant itself onto the endometrium, and confirm conception.

The foetus doesn’t give up easily either, as its own survival is in question. Remember that this is an arms race, so the foetus has to evolve some defence in order to ensure its own survival.

Source: Google

In the majority of the mammals, the placenta just interfaces with the mother’s blood supply, allowing nutrients to diffuse into the uterus; this way, the mother decides how much of her nutrition supply goes to the developing foetus. This is not the case in hemochorial placenta-bearing mammals, such as mice, primates and humans. This evolution allows the foetus to penetrate through to the mother’s blood directly, and paralyzing her arteries, restricting their constriction. The foetus now has unrestricted access and takes full advantage of this.

Human chorionic gonadotropin (hCG) is a hormone secreted by the developing foetus that has many varied functions, including stimulating the mother to produce progesterone (that increases the blood flow to the uterus) and evade the immune cells of the mother during the first trimester. Once the embryo has implanted itself on the endometrium, and has direct access to the mother’s blood, it secretes hCG into the blood, hijacking her pituitary to produce the hormone. It later starts producing its own hCG preventing the mother from spontaneously aborting the foetus.

How we can observe this evident arms race

The mother’s drop in blood sugar during the early stages of pregnancy maybe one such evidence- her way of off-setting the foetus’s future demands. The placenta secretes a hormone called human placental lactogen (hPL), increases insulin resistance in the mother, making the blood glucose levels remain high right after a meal. As long as the glucose remains in th blood, it is up for grabs, and the foetus secretes hPL to ensure that it gets the glucose. In some cases, this leads to gestational diabetes in the mother.

Still think the mother’s love is purely unselfish?

Mother-child relationships are portrayed as an idealistic, completely altruistic and an act of eternal love, while the first contact the mother has with the foetus is one of competition for survival, for both of them. It is indeed a huge paradox! The next time your mother takes an extra effort for you, appreciate it. You stole her nutrients, hijacked her brain and made her carry you around for nine months, so enjoy while you can, because the competition only gets tougher.


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