Judaism is more than simply a religion; it’s also a family, a heritage, and a connection spanning thousands of generations. Yet “Jewish identity” can come in a variety of forms. We could be descendants of Abraham and Sarah. We could be Jews by choice. We could be Ashkenazic, Sephardic, Mizrahi, or some mix. And different communities may accept or reject others’ definition of Jewish identity. 

But in contrast to identity, ancestry is not a matter of opinion; it is a part of nature. Ancestry depends on natural selection, a principle that depends on life’s presence on Earth for a very long time. We cannot choose our DNA, our history, or where we came from, and we most certainly cannot reject the universal (and shared) human origin story.

So this question of identity, the “who we are,” is both a Jewish question and scientific question. All human beings — and indeed, all of life — are connected and share ancestry, yet DNA is also what makes each individual person unique. We are inextricably tied to our biological family, and yet we can also choose the community we want to be a part of. So how do these questions of ancestry and identity, of similarities and uniqueness, help us shed light on our biological origins, as well as our relationship to the Jewish community today? 

Imagine the approximately 13.7 billion years since the beginning of space-time as being recorded in a set of books. The bindings on each volume are an index of the kinds of life that were here in the periods they represent. If each book had 450 pages, and each page were to record a million years, then each volume would be the passage of 450 million years, and 30 volumes would come out to be 13.5 billion years. 

The sun and the earth both formed about 4.5 billion years ago, a time recorded on the pages of volume 20. 

The period punctuating the last sentence of Volume 30 would represent the past few hundred years, and so it would bring us to the present moment. The width of that simple dot records the time since science has taken hold of our imaginations as a way to understand all this.

How has life emerged on our planet over 4 billion years, in all its wondrous diversity? Nature teaches us that living things – and all other things we have found to date – are made of atoms. In On the Nature of Things, the Roman poet-philosopher Lucretius imagined this was the case, about 2000 years ago: “Therefore, the supposition that, as there are many letters common to many words so there are many elements common to many things, is preferable to the view that anything can come into being without elementary particles.” 

The notion of “many letters common to many words” brings us to DNA, the “text” out of which our ancestry is made.

What sort of vine is this guy climbing? Sometime more than four billion years ago, in the period recorded in volume 21, a molecule called DNA first came together as an assembly of atoms, of the sort Lucretius was so prescient about. This molecule has remained with us today because of the singular properties it had and still has.

DNA is a text. Using a four-letter alphabet of base pairs, it encodes information in its base-pair sequence in a manner much like printed words. But unlike written text, these letters are assembled from only a few dozen atoms each. Also unlike our writing systems, DNA has the capacity to act at once as both book and scribe, making copies of itself.

At a bare minimum, the DNA of a living organism must encode information for the construction of proteins. To copy the DNA itself, it separates the two strands, then sews in the complementary halves of each strand to make two copies of DNA from one. In addition to encoding the proteins that copy it, a living being’s DNA must encode the totality of the proteins that assemble into the cells of the organism.

Having encoded such extensive and complicated protein assembly instructions, the DNA also must encode when they are turned on and turned off, with variations both in time and location within the body. This allows for the differentiation of the body into different tissues, all emerging from one fertilized egg cell.

The regulatory information encoded by the DNA is subtle, and though the body fully understands it, we do not. We do understand, though, that all living things, including humans, are built from proteins encoded by DNA sequences that are subject to such regulation.

The DNA of a person is organized in a sequence of texts much like the volumes of an encyclopedia. More than a century ago, scientists first conceptualized the human DNA held by the cells of the body as a set of “volumes,” the 23 pairs of separate human chromosomes. But because of gene regulation, the DNA of a person is much more a set of programs than it is an encyclopedia.1This is despite the coincidence of the 11th edition of the Encyclopedia Britannica coming in 23 volumes and a person’s DNA being separated into 23 pairs of chromosomes.

The DNA regulatory programs for different tissues are set aside in different volumes, but not at all the same as the chromosomes in which they are found. The circuitry of regulation can reach across the entire genome to turn sets of genes on or off.

We have much to learn about the cascades of changes that allow a fertilized egg – the first cell of what will grow into a plant or animal – to regulate its DNA transcription so that its two daughter cells, and all their billions of progeny, are launched into separate cascades of differentiation.

Here, three examples of such cascades have spilled out into three developing embryos, to yield a boy, the lizard on his shoulder, and the turtle in his hands. The wallpaper behind them shows the forms their respective embryos took as they differentiated from their respective fertilized eggs.

Why do these three have such similar forms in their earliest embryonic stages, and could the answer lie in DNA sequences the three still have in common, even as young adults? But how could they share sequences when there are so many possible sequences that DNAs can have?


Imagine that a comic with a dull wit wears a poster-board that describes his performance: “act a gag, act a gag, act.” He tells you that that is also his name. He then tells you that you cannot have that name, because it belongs to him. He tells you not to worry, there’s a sequence just for you, and a different one for everyone, just not this one.

And he then explains – he is not a good comic, but is a well-informed one – that his name is one of 417 possible DNA stretches, each a different sequence of the four letters A, C, T and G. You do the calculation and find that 417 is about 1.7 x 1010 possible “names.”

That means there are more than 17 billion possible DNA stretches of that length, more than twice as many as there are people on the planet today.


Now we come to the heart of the matter of ancestry.

Since we each have our own DNA sequence of not 17 base pairs like the clown’s poster-board, but 6 billion base pairs, in our chromosomes, all of us are unimaginably rare, absolutely unique at birth. How then can it be that even so, all living things share DNA sequences? This is the question Darwin asked before we knew about DNA, about the similar shapes and functions it encodes in the millions of different kinds of living things.

Species that are as incommensurately different as frog and peach, beetle and elephant, roach and rose, or even chimp and professor, have overall sequence similarities in their genomes that range between 98% for the professor and the chimp, down to a small but real overlap of sequences even for the roach and the rose or the beetle and the elephant.

This is a real paradox: how can the DNA sequences in these species and all the others be related to one-another, rather than being distributed evenly through the vast informational richness of all possible long DNA sequences?

The solution is simply to beg the question and say: the DNAs of all species are related to one another. And then, because DNA replicates semi-conservatively, the penny can drop: if all current DNAs are related to one another, all current species must have a common ancestor.

More than 150 years ago, a hundred years before DNA’s capacity to copy itself was understood, Charles Darwin imagined this as the consequence of a positive feedback loop that selected for the survival of different variations under different conditions. 

The feedback loop of change that is critical to a DNA sequence’s survival is represented here by a slot machine. The handle of the slot machine is a chromosome and the spinning wheels are ancestral species. They have rolled and come up with three ancestral mammals, from a species that might have died out a hundred million years ago.

The elephant, boar, anteater, dog, seal and bat are a sampling of the winners of that initial roll of the DNA slot machine 65 million years ago. We are members of the current set of survivors, today’s species of mammals.

The generality is stunning: all species of life, and all living things of any species, are mortal. No matter how different, they share their current viability and their common ancestry, but through the ravages of time, only the latter is permanent.

No random mutations that would have altered the early blueprint of embryonic development in each species have survived from the time of the last ancestor shared by humans, lizards and turtles. That is why the early embryos of a boy, a lizard, and a turtle are so similar.

The generalization is simple: every nucleus of every cell of everything alive today is a repository of past wisdom in the form of texts that continue to inform the present. In that, a cell’s nucleus is like the site of the ancient Temple in the walled city of Jerusalem. Turning from form to function, let us turn from architecture to sacred texts.

Darwin counted our unique mental capacities among the rewards of natural selection for us as a species. On a foundation of neural circuitry we have built temples in our mind, often with a personification, like Athena, of a wisdom we hope we may attain. In Jewish terms we see this in the ancient wisdom of Sanhedrin 4:5 – “whoever saves one life […] saves an entire world.” What a great success natural selection has found in us!

Or, perhaps not. DNA does not encode a thought, only the capacity for thought. Ideas are not subject to the feedback loop of natural selection; that’s the reason for our spectacularly disproportionate success at proliferating. We have broken out of natural selection’s slow sieve of mutation; we can simply have an idea, and choose to act on it. No need to wait for natural selection’s positive feedback loop to select for a DNA variation that permits that new idea. Any brain can have any idea, any time.

Human genetic variation between different ancestral backgrounds is much less than once thought. So the joke of our imagination is on nature, but as a consequence it is on us as well. Our minds can encompass nature, but they can also go beyond it, and imagine things that need not be possible in nature. When we do that, we may escape nature for a while, but in the end, these flowerings of the mind will be brought back into alignment with the facts of nature by the fact of species mortality. If there is one place for imagination to generate wisdom, that would be the place.


And that brings us to Jewish ancestry and Jewish identity. Jewish identity is grounded in our mental subjective worlds, not in any of our specific DNA sequences. These sequences can surely tell us where our ancestors have lived in past centuries, but they have no capacity to tell us how we have learned from them, or from others not related by ancestry, or what it means to any of us to be a Jew. Our Jewish identity emerges and survives by our acceptance of the importance of certain texts, and by our shared willingness to re-interpret the meanings of those texts so that they help us as we make our own paths through life. 

As it is subject to the choices of every generation, Jewish identity is fluid. The paths we take are not inherited, they are learned, and they are chosen by each of us. But this makes Jewish identity no less important a determinant of how we live our lives. As Rabbi Hillel said to a prospective convert 2,000 years ago, so each of us can and should say to ourselves, often: “What is hateful to you, do not do to your fellow: this is the whole Torah; the rest is the explanation; go and learn.”


When we do that, when we enter social relationships with utmost humility, seriousness and mutual respect, we are Jews. When we learn those habits of mind and soul from our parents, we share a Jewish ancestry. When we learn them only later in life from strangers who become our teachers, and when then we choose them and live by them, we share a Jewish identity even so.

Let me close with a quote from Maimonides, Mishneh Torah, Hilchot Talmud Torah, Chapter 3:

“The people of Israel were crowned with three crowns: the crown of Torah, the crown of priesthood and the crown of sovereignty. The crown of priesthood was acquired by Aaron, even as it is said: “And it shall be unto him, and to his seed after him, the covenant of everlasting priesthood” (Num. 25.13); the crown of sovereignty was acquired by David, even as it is said: “His seed shall endure forever, and his throne as the sun before Me” (Psalms 89.37); but the crown of the Torah, behold it, there it lies ready within the grasp of all Israel, even as it is said: “Moses commanded us a Law, an inheritance of the congregation of Jacob” (Deut. 33.4), Whosoever wants it may come and take it.”  

There cannot be a single definition of Jewish Identity. I know of no better example of this in our sacred texts than the story of Ruth, the Moabite woman who chose to stay with Naomi the Israelite, and who thereby went on to become the ancestor of King David. It is as simple as this: to live by the law of Moses, we must choose to be in the congregation of Jacob. We must also want to live by that Law, and then we can simply come and take it; that is, we can simply be Jewish.

(This post is part of Sinai and Synapses’ project Scientists in Synagogues, a grass-roots program to offer Jews opportunities to explore the most interesting and pressing questions surrounding Judaism and science. Dr. Bob Pollack is Acting President of West End Synagogue, as well as Professor of Biological Sciences at Columbia University, a AAAS fellow, and a former member of Advisory Board of the John Templeton Foundation. He and his wife, the artist Amy Pollack, worked together to produce the book “The Course of Nature: A Book of Drawings on Natural Selection and Its Consequences,” which explores many of these issues in more depth).

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1. This is despite the coincidence of the 11th edition of the Encyclopedia Britannica coming in 23 volumes and a person’s DNA being separated into 23 pairs of chromosomes.