Tag Archives: Genetics

Why is Judaism Matrilineal?

In this week’s parasha, Va’etchanan, God cautions His people about intermarriage (Deuteronomy 7:3-4). Although the Torah is speaking specifically about intermarrying with the Canaanite nations, the verses have always been understood as prohibiting intermarriage with any and all other nations. This is especially true because the Torah goes on to say that intermarrying will lead to the children being led astray and being turned to idolatrous ways. In those days, the Canaanites were not the only idolaters, of course—just about everyone was an idol-worshipper—so all intermarriage was forbidden. The Torah phrases the prohibition in an interesting way:

You shall not intermarry with them; you shall not give your daughter to his son, and you shall not take his daughter for your son, for they will turn away your son from following Me, and they will worship the gods of others…

While the Torah makes it clear that one must not marry their son to a gentile woman, or their daughter to a gentile man, it goes on to only mention that the son will be turned away from God, not the daughter. The Sages explain that women tend to be of greater faith than me, and as the primary builders of the home, it is the women who set the spiritual tone of the family. A faithful Jewish man who marries a non-Jewish woman will, sooner or later, be led astray. Such was the case with a great many Jewish men following the Babylonian Exile, and when they finally returned to Israel, they admitted (Ezra 10:2-3):

We have broken faith with our God, and have married foreign women of the peoples of the land; yet now there is hope for Israel concerning this thing. Now therefore let us make a covenant with our God to put away all the wives, and such as are born of them, according to the counsel of Hashem, and of those that tremble at the commandment of our God; and let it be done according to the law.

“Ezra reading the Law in the hearing of the people” by Gustave Doré

From all of the above, the Sages conclude that Judaism passes on maternally. Scripture makes it clear that only the non-Jewish mother will turn a Jewish man astray, and as we learn from Ezra, only those born to “foreign women” are not part of the Covenant. Aside from this, there are a number of other practical and spiritual reasons why Judaism must be matrilineal.

Since the mother is the one actually giving birth to the child, it is pretty much clear every single time who the child’s mother is. The same cannot be said of the father. Throughout history, when raping and pillaging was unfortunately very common, and there were no paternity tests, only the mother’s status as parent was evident. This may be why the ancient Greeks and Romans tended to be matrilineal as well.

Shaye J.D. Cohen points out (see chapter 9 of The Beginnings of Jewishness) that in Athens, only the offspring of an Athenian man and an Athenian woman could have Athenian citizenship, a law introduced by Pericles around 451 BCE. If an Athenian man married a foreign woman, the children would not be Athenians. Later, the Romans similarly held that only two Roman citizens can have a child who was a Roman citizen, and if a Roman married a foreigner or someone of a lower social class, the status or identity of the child would be that of the mother.

While these rules make sense from a logical perspective, they also recognize the profound connection that a child and mother have—far superior to that of child and father. And this ties into the deeper biological, and spiritual, reasons for why Judaism is matrilineal.

The Genetics of Motherhood

When it comes to the genes and traits of children, people tend to think that they are a 50-50 mix of mother and father. We learn in school how 23 chromosomes from the father (carried by sperm cells) meet 23 chromosomes from the mother (in the egg cell) to produce a new child. We are made to believe that even if the child may look more like one parent, they are nonetheless perfectly half-half. This is completely untrue.

A karyotype showing 23 pairs of chromosomes. (Credit: National Human Genome Research Institute)

First of all, when it comes to boys, the Y chromosome of the father is far smaller and carries significantly less genes than the mother’s X chromosome. Girls do have half of their father’s and half of their mother’s genes (receiving an X from each, along with the other 22 chromosomes). However, this only refers to nuclear DNA. The cell has other forms of heritable genetic material, too, most notably in mitochondria.

The mitochondrion is one of the most vital components of any cell, and provides the bulk of a cell’s energy. The main reason that you breathe is to provide oxygen for mitochondria. They are involved in countless processes, including calcium storage, cell signalling and communication, metabolism, hormone production, the breakdown of wastes (such as toxic ammonia in the liver), and apoptosis, or cellular death. A single cell could have over a thousand mitochondria.

Mitochondria under a microscope.

These mitochondria have their very own DNA, carrying hundreds of additional genes. This DNA, called mtDNA, is passed down strictly from mother to child. A father’s mitochondria play no role. In fact, because of this, geneticists are able to trace a person’s maternal lineage fairly accurately thousands of years into the past by analyzing mtDNA. (My own mtDNA—haplogroup U6a—dates back to a woman who lived in North Africa about 1000 generations ago!)

There are multiple other cellular components that are passed down almost entirely from mother to child. Because the sperm essentially donates only its nucleus (with its chromosomes) to the egg, it is the egg cell itself that begins to divide in producing an embryo. Thus, the bulk of a person’s cellular structure comes from their mother, too. Back in university, I had one biology professor who estimated that inheritance is not 50-50, but more like 80-20. From a scientific perspective, we are far, far more like our mothers.

This is one reason why mothers have such a deep and profound connection to their child. Amazingly, scientists have recently discovered that when a woman is pregnant, DNA (and whole cells) from the child actually goes into the bloodstream and ends up in the mother’s brain! Fetal cells have also been found in lungs, muscles, and heart tissue of mothers. A mother will literally carry the DNA of her children in her body for the rest of her life.

Just as children are physically more connected with their mothers so, too, are they more spiritually connected to their mothers. (After all, one of Judaism’s central principles is that the dynamics of this physical world are only a reflection of the spiritual realms.) And this is yet another key reason why Judaism is, and must be, matrilineal.

What About Conversion?

The genetics perspective brings up an important question: what about converts? A person who converts to Judaism is, of course, a full-fledged Jew. But their DNA hasn’t changed! It goes without saying that Judaism is not genetic, and the discussion of genetics above is meant to only be an analogy for spiritual processes.

Having said that, we have an opportunity here to bust another common myth: that a person’s DNA is unchanging. People are often taught that whatever DNA they are born with, they are stuck with. If they have a defective gene for a particular condition, then they will definitely develop that condition. Today we know that this, too, is not entirely correct.

As discussed before in detail, our body has epigenetic machinery which allows gene expression to be controlled. Just because a person has a certain gene does not mean that the gene will be operational. It can certainly be “shut off”. While it was once thought that our lifestyle choices have no impact on our genes or epigenetics, new research continues to show that the choices we make have a tremendous effect on our genes. We’ve known for a long time that things like diet and physical activity impact gene expression, and now we even have evidence that prayer and meditation affects our genes.

Therefore, a person who sincerely converts to Judaism, and begins to live a Jewish lifestyle, eat like a Jew, think like a Jew, and pray like a Jew, will very likely experience changes on the genetic (or epigenetic) level as well. And these epigenetic changes are hereditary.

This is yet another reason why it is so important to convert to Judaism properly. Converting means not only converting in name, but becoming Torah-observant and living a Jewish life. Otherwise, what’s the point of the conversion? This is precisely why Orthodox conversions tends to be so difficult and time-consuming. The rabbis want to ensure (as much as possible) that the person is serious about becoming a Jew, and will actually live as one.

The process is far from perfect, and sometimes they do make it too difficult and tedious. We have addressed this in the past as well. Some point out that it was never so difficult to convert in past centuries. This is true, as the Talmud (Yevamot 47b) explains the procedure thus:

Once healed [from circumcision], we immerse him immediately; and two scholars stand above him, and teach him a few easy commandments and a few difficult commandments. Once he has immersed and come up from immersion, he is part of Israel for all matters. If the convert is a woman, women sit her in the water up to her neck and two scholars stand outside, and teach her a few easy commandments and a few difficult commandments.

That’s all it took back in those days. A person was just taught a few introductory mitzvot while already immersed part way in a mikveh. They would pick up the rest when going on to live as Jews and marry into Jewish families. Even in the time of the Rambam (Rabbi Moshe ben Maimon, 1135-1204) hundreds of years later, he codifies this exact procedure as law (Mishneh Torah, Issurei Biah 14:6). Yet, in those days just about everyone was religious (whether Jewish or not). This isn’t the case in today’s secular society. A person who converts to Judaism wouldn’t necessarily learn how to be a Jew by simply marrying into a Jewish family. It is necessary to carefully teach them everything beforehand.

It is just as necessary to determine their real intentions, and affirm their absolute sincerity. In a world where people change their identities faster than they change their socks, it isn’t surprising that Orthodox rabbis take conversion very seriously and are extremely stringent about it. It is important to keep this in mind as we continue to hear about intermarriage and the “who is a Jew?” debate in the mainstream media.

Jacob’s Sheep: Genetics and Epigenetics in the Torah

geneticsThis week’s parasha is Vayetze, where we read of Jacob’s arrival in Charan and the details of his twenty-year sojourn there. During this time, Jacob married (twice), had a dozen children, and toiled for his cruel father-in-law Laban. Laban recognized that he had been blessed exceedingly on account of Jacob’s presence, and offered him a new wage for his labour. By this point, Jacob knew not to trust the sly Laban, and asked simply for ownership of all the speckled and spotted sheep. Since these imperfect-looking sheep were few in number, Laban readily agreed. It appears that both Laban and Jacob were well aware of the basic principles of genetics. Today, we know that sheep have 17 or so different colour alleles, and white colour is the dominant one.

For those who have forgotten high school biology: An allele is a variation of a gene. So, for example, all humans have a gene for eye colour, but have different alleles that code for the varying colours: some have alleles for blue eyes, while others have brown eyes, etc. Each person has two alleles for every gene – one from their mother, and one from their father. Certain alleles are “dominant”, while others are “recessive”. Dominant alleles are far more likely to be expressed. In humans, brown eye colour is dominant to blue eye colour, which is why some 55% of people have brown eyes, while only about 8% have blue eyes.

Basic "Punnet squares" showing the probabilities of eye colour for the children of fully brown-eyed and blue-eyed parents, and a brown-eyed parent who carries a blue allele.

Basic “Punnet squares” showing the probabilities of eye colour for the children of fully brown-eyed and blue-eyed parents, and a brown-eyed parent who carries a blue allele. (Courtesy: The University of North Carolina at Chapel Hill)

White is the dominant allele for sheep colour, so Laban assumed he was getting a terrific deal from Jacob, who was apparently ignorant of sheep genetics. In reality, Jacob knew sheep genetics quite well, and had something else up his sleeve. He only offered Laban this deal because he knew the greedy Laban would readily agree to it. So, how would Jacob outwit his father-in-law?

A Brief Introduction to Epigenetics

Jacob was evidently a far more knowledgeable geneticist than Laban, as he was aware of a concept that has only come to light in recent decades, called epigenetics. Epigenetics refers to various layers of heritability and genetic effects which are above, or outside of (hence the Greek prefix epi), the actual genetic code. In 2008, scientists defined an epigenetic trait as “stably heritable phenotype resulting from changes in a chromosome without alterations in the DNA sequence.” In simple terms: the chromosome that contains the genes is altered in some way without affecting the DNA sequence (the genetic code) itself. That alteration is heritable, too, and passed down from one generation to the next.

A number of epigenetic mechanisms have been discovered. The most common are methylations and acetylations, where small molecules are attached or removed from the DNA strand, causing it to coil either more tightly or less tightly. When the DNA coils more tightly, the gene is rendered inaccessible, and cannot be expressed. If uncoiled, the gene is exposed, and can be translated into the protein it codes for, thus expressing the trait.

Coiling of DNA and gene expression. (Courtesy: National Institutes of Health)

Coiling of DNA and gene expression. (Courtesy: National Institutes of Health)

While epigenetics is quite complicated, its implications are tremendous. What it means in practical terms is that even though a person has a certain gene, that gene does not necessarily have to be expressed, as it can be silenced through epigenetic mechanisms. For example, a person who has a gene that predisposes them to cancer, God forbid, could potentially have that gene suppressed, thus eliminating their increased cancer risk. (Though they don’t work in this precise fashion, epigenetic cancer drugs are now available.) This also applies to people who might be genetically predisposed to obesity, diabetes, Alzheimer’s, or theoretically, any trait at all. A person who has both brown and blue alleles does not necessarily have to have brown eyes (which is what we would expect based on principles of classical, or Mendelian, genetics). The brown eye allele can be silenced, allowing the blue allele to be expressed fully.

The same is true for Jacob’s sheep. While the alleles for speckled and spotted sheep are recessive, the dominant white allele can be suppressed, resulting in more speckled and spotted sheep. In the Torah, we read how Jacob took tree branches and stripped away some of their bark to expose the inner white layers so that their pattern resembled that of the speckled and spotted sheep. He then placed these branches in front of the white sheep that were mating, and this resulted in the white sheep producing more speckled and spotted offspring. In this way, Jacob was quickly able to multiply the number of irregular-looking sheep in the flocks, increasing his own wealth, and leaving Laban in utter surprise.

What does science have to say about this? Is it really possible for the white sheep to produce speckled and spotted offspring just by looking at speckled and spotted tree branches? Which factors actually affect epigenetics?

The Epigenetics Revolution

In northern Sweden lies a small, isolated town called Överkalix. This town kept detailed historical records, including births, illnesses, and deaths, as well as harvests and food prices. Researchers started poring over this data and noted a number of emerging patterns. Surprisingly, those who grew up in times of relative abundance tended to live shorter and sicker lives, while those who grew up in times of relative famine were healthier and lived longer! Even more shocking was that these traits passed on to their children and grandchildren. The grandsons of those who grew up in times of abundance lived roughly six years less than grandsons of those who grew up in times of famine!

The Överkalix study opened the door to much more research on the subject, and today we know that not only does food impact our epigenetics, but so does smoking, alcohol, exercise, and just about every lifestyle choice we make. Moreover, recent studies find that not only do our actions impact our epigenetics, but even our thoughts do! In 2013, scientists discovered that meditation affects epigenetic mechanisms and results in, among other things, less inflammation in the body, better stress responses, and faster mental processes.

TIME Magazine Feature on Epigenetics

TIME Magazine Feature on Epigenetics

Epigenetics has brought about a revolution in biology, and a new realization that we are not slaves to our genome. We are very much in control of how our genes operate, and seemingly every choice we make affects our health and wellbeing, as well as the health and wellbeing of our children and grandchildren, since these epigenetic patterns are heritable. This is one of the most enlightening and liberating scientific findings, putting each person in the driver’s seat of their biological fate. It should also motivate us to make healthy lifestyle choices because, even if we might not care so much about our own health, the health of our offspring is directly impacted by our choices.

The Return of Jacob’s Sheep

If meditation plays a role in how our genes are expressed, there is no reason why other mental processes cannot do the same. By visually exposing his sheep to speckled and spotted images, Jacob may very well have triggered an epigenetic change resulting in suppression of white alleles. Neurologists have long known that there is essentially no difference in brain patterns when a person is literally seeing something versus when they are simply visualizing the same thing. If mental visualizations like meditation can affect the epigenome, then why not actual visual displays? Armed with this knowledge, Jacob outwitted his father-in-law and became an exceedingly wealthy man.

Of course, one cannot deny God’s role in the process, as Jacob himself explained to his wives (Genesis 31:7-9):

…your father mocked me and changed my wages ten times, but God did not permit him to harm me. If he would say, “Speckled ones shall be your wages,” all the animals would bear speckled ones, and if he would say, “Ringed ones shall be your wages,” all the animals would bear ringed ones. Thus, God separated your father’s livestock and gave it to me…

Changing one’s epigenetics is not so simple! As with everything else, a little help from Above is always needed. Jacob put in his effort by exposing the animals to stimulating sights, and God took care of the rest.

Jacob's sheep are unique not only in their colour, but also in that the rams have extra horns.

Jacob’s sheep are unique not only in their colour, but also in that the rams have extra horns.

Interestingly, this week saw the arrival of 119 “Jacob’s sheep” to Israel. This ancient breed of sheep originated in the Middle East approximately 5000 years ago. They were extirpated from the land of Israel long ago, but thankfully some survived and were brought across North Africa to Europe and finally America. The rare speckled and spotted sheep are in the Holy Land once more, perhaps a sign of the forthcoming return of all of Jacob’s children to their ancestral home.