We are still in the adolescent stages of genetics, the study of DNA. We still do not know everything and the Human Genome Project has flooded us with information that we do not, as yet, fully understand. Epigenetics, the study of the proteins that surround the central helical ladder of DNA, really is in its infancy. Epigenetics are important because it is these chromosomal proteins that act as regulators and on/off switches for the DNA. They decide the activity of the DNA genes that we have.
The new subject of epigenetics is of great importance in this discussion. The questions asked here have not been asked elsewhere. Nobody has thought to ask them so no investigation has been done. There are no answers.
When objective evidence is lacking, subjectivity always creeps in and makes the decision.
The reason that science wholeheartedly believes in the former theory and will not consider the latter is historical and anybody who has been taught genetics has been heavily indoctrinated in this unquestionable 'truth'. This 'truth', that it is the sperm that decides gender, was an inevitable conclusion in a misogynistic society. It was the next step from the theory, a quite bizarre misogynist theory, that the father contributed the entire life essence of a child that the womb of the mother only nurtured.
There are certainly precedents in a process of excluding societally motivated, machista beliefs from genetics and reproduction using the evidence.
It took a very long time for science to even conceive of the possibility that the mother might contribute the majority of inherited material to a child but it is proven. The father only contributes 50% of the chromosomal DNA but that is not the only form of chemical inheritance in the cell. Much of the contents of the cell are self generating and self reproducing. They come from the egg and the egg alone.
So we should perhaps suspect and question any theory of genetics, reproduction and evolution that we have inherited from a misogynist past of subjective bias. The She-Devil's Advocate of objectivity would propose and try to justify theories that might well have arisen if science had a matriarchal rather than patriachal past. A female dominated society would obviously have promoted the belief that the mother was more important than the father.....
Two Types of X Chromosome
All X chromosomes are not equal. There are two distinct types of X chromosome in a human cell. One is active and acts like any other chromosome. It is in the centre of the cell nucleus and engages in metabolic functions, such as the production of proteins.
Everybody, male and female, has one of these active X chromosomes in every cell. A cell is in metabolic balance with a single, functional X chromosome. So what happens to the second X chromosome of the XX female?
The second X chromosome of the female would overload the cell and make it imbalanced. What has evolved is that this second chromosome is excluded to the edge of the nucleus of the cell where it is largely inactive in genetic and metabolic terms. It is called the Barr Body and little is really understood about it. Investigations into the Barr Body are still ongoing.
The question is whether the Barr Body is simply functionally different to the active X chromosome but in every other way the same or whether there is some profound difference between and active X chromosome and a Barr X chromosome. It boils down to a question of whether the X chromosomes are readily interchangeable; an active X can change into a Barr X. If they can change, how easily and how often does it happen.
The functional difference is not about DNA but about function and activity. Perhaps the answers are Epigenetic rather than Genetic in terms of DNA.... that is where the on/off regulators are to be found.
If the difference between an active X chromosome and a Barr X chromosome are Epigenetic, we may speculate using the general first principles of Epigenetics. The proteins of the epigenes are more fluid and susceptible to change in life in response to the internal environment of the body. However, that is not to say that they change easily. Epigenes are inherited and they can endure for human generations without changing. It can take decades or a century for an epigene to change. In practical terms of cell division, that is an age.
The epigenetics of X chromosome that decides whether they will be active or the Barr variant can change but in reality, it happens very rarely. An active X chromosome will usually stay as an active X chromosome. A Barr X chromosome will probably always stay as a Barr X chromosome.
In effect, women are only superficially XX. To be more precisem they are, in practical epigenetic terms, XB.
The Inheritance of X and B
So half of the eggs will contain an X chromosome. The other half will contain a B chromosome.
Half the sperm carry an X chromosome and the other half carry a Y chromosome.
All males are XY and all females are XB.
That means that only Y sperm can fertilise an X egg and the B egg requires an X sperm.
BY is incompatible with life at a cellular level because there is no active X chromosome. XX is incompatible with life because there is a 'X-overload'.
The outcome is that eggs have predetermined gender. It may go beyond that. They may even select which gender of sperm can actually penetrate them gelatinous layer.
In general, Mother Nature does not like waste. It is quite conceivable that there is an unknown selection process has evolved that we have never suspected. Hence we have never looked for it.
Well that would explain why IVF programs that bypass the process of the sperm penetrating the gelatinous layer of the egg by injecting the sperm directly into the nucleus have approximately double the immediate failure rate of the natural process.
A Better Fit With Global Evidence
So there are two possible hypotheses here. Either the eggs are generic in gender terms and any sperm can fertilise any egg, hence determining gender, or the active X and Barr X are epigentically distinct, which would imply that the egg has a predetermined gender.
And we do not yet know enough about Epigenetics to confirm or refute either argument. It is simply too early to decide. Both should be on the table until conclusive evidence is available.
So against academic tradition, I will not decide or run a first past the post popuarity contest to decide the winner and exclude the possibility of the other for all time. Academic science has done enough of that, an example being the decision to definitively choose Darwinism over Lamarckism before they had sufficient evidence to exclude Lamarckism occuring over an evolutionary timescale.
I return to the basics of formal logic and Ockham's Razor. In the debate, the simplest theory which can explain the widest scope of the evidence with the least assumptions should be preferred. This is used and placed into practice in clinical thinking so I am familiar with its real world application. If a patient's symptoms, signs and test results can all be explained by a single diagnosis that is to be 'preferred' but a diabetic can still break a leg, in which case two diagnoses co-exist.
The concept of 'preferred in the debate' is essential. The debate can say that one theory is 60% likely whilst the other is 40% probable given present, incomplete knowledge. The ratio could be 95% to 5% but that still does not mean that the improbable theory is disproven or untrue. It should still be kept in mind as a possibility. The question should stay open and it should be researched.
And what decides the percentage ratio for theories under debate is consistency with the globally available evidence. The doubling of IVF embryonic failure rates from injcting sperm into eggs is one piece of circumstantial, corroborrating evidence. It is hard evidence that the 'eggs have predetermined gender' can explain but the hypothesis that sperms dictate gender cannot explain.
Another piece of circumstantial evidence that is suggestive of the eggs having gender is that the diet of the mother has been proven to have a significant effect on gender. The folk wisdom that butchers rarely have daughters has been proven by the evidence but it was found to be the mother's diet that was important, not the father's.
The easiest explanation of this is that the egg race, a race for the eggs to mature in the ovaries under hormonal stimulation considering the internal chemical environment in which they find themselves, influences the probability of which gender of egg is released. This fits better with the eggs having predetermined gender.
What Do I Believe?
I do not believe. I hypothesise.
I am also relaxed about saying that I do not know. We, with all of our scientific knowledge, do not know, at least not yet. In fact, I am excited at the prospect of new discovery....
Having looked at the commonly available evidence and thought about it with an open mind, I lean slightly towards the 'eggs have gender' hypothesis but I may well be wrong. I will call that my 60% hypothesis and the more traditional belief a 40% hypothesis.