New genetic research confirms the Bible was right: species don’t mix!
The mule is a problem for Darwin and the Bible
A deep mystery haunts both Charles Darwin and the Torah—a riddle embodied in one humble creature: the mule. It’s a hybrid, born of the mating of a horse and a donkey, but unable to have offspring of its own. It’s sterile. For Darwin, this was not just a barnyard curiosity. It was the “mystery of mysteries,” that rocked the foundation of his otherwise beautiful evolutionary theory.
If new species arise by gradual change and interbreeding and evolution is a continuum, why are hybrids like the mule sterile? Why do the boundaries between species seem so stubborn, so absolute? If hybrids are sterile, how can new species ever arise?
This wasn’t just a technical glitch in his theory; it was a fundamental paradox. Darwin wrestled with it in On the Origin of Species (1859), devoting an entire chapter to hybrids and their sterility. For decades, scientists shrugged off these limits as quirks of genetics or chance. This “mule paradox” remained a central problem in evolutionary biology until just a decade ago.
For the Torah, the mule is also a problem. The Torah’s strictly prohibits the crossbreeding of species, the mixing of seeds, and even the weaving of wool and linen together, the laws of kilayim[1]. The Talmud singles out Anah, the first breeder of mules.[2] Anah was himself the bastard offspring of incest between his father and grandmother.[3] For Torah, the mule is a living symbol of disorder—a breach in the divinely ordered tapestry of life. If God created each species “according to its kind,” what does it mean when humans force a breach in those kinds?
Jewish tradition says there are mystical reasons to reinforce the boundaries between species. Mixing them is called “kilayim” and the Torah strictly forbids it and the Jewish tradition elaborates all sorts of examples of this abomination.
Science says, “God Don’t Make No Junk!”
Astonishingly, in the last two decades has genetics shown that the Bible was right. Science discovered vast stretches of DNA that didn’t code for anything, it thought. It labelled this useless DNA “junk.” However, new research has discovered that among many other functions, this junk actually is crucial in enforcing reproductive boundaries between species. The ENCODE project (2003–2012)[4] and subsequent research pinpointed the chromosomes and genes that act as barriers to successful hybridization in several species.[4][5] In other words, Darwin was right to fret about mules. There are no hybrids because deeply embedded genetic mechanisms prevent it.[5] Non-coding DNA is not junk at all, but a sophisticated regulatory network. As the t-shirt says, “God don’t make no junk!”
The “Hard Stop”: What the Numbers Show
Based on the latest studies of our own part of the evolutionary tree, the number of times primates from different species hybridize to produce living offspring is very, very tiny. This is true whether hybrid attempts occur in nature or if a modern day Anah in a lab tried to force interbreeding. Even using sophisticated genetic manipulation, hybridizing has never led to viable multicellular organisms. In other words, the genetic “hard stop” of species interbreeding is the rule. Any interspeciation is a short-lived freak of nature. Even in the event such mating does produce offspring, the number of times those offspring themselves are fertile to produce other offspring – so there can be progress or novelty in evolution – is also tiny. The chances of a new, stable, fertile lineage is infinitesimally small. Fewer than 1 in 100,000,000. Functionally zero.
The Hebrew when translated properly reveals the secret
Then, as if the Biblical text is signaling that it knows a deeper truth, there’s the puzzle of the Hebrew word itself – kilayim. One English translation is “…Do not cross-breed your cattle with different species (“kilayim”) “[Lev. 19:19] But the Hebrew “kilayim” is more mysterious. Scholars believe it alludes to “restraints” or “holding back.” When the Bible revisits the prohibition, it tells us the consequence of breaking the rule of mixing two species. The best Hebrew translation is “the fullness of the produce will be rejected.” Taken together, the Hebrew now appears as prophetic. Individuals from different species may want to breed together, or humans may want to experiment and force them together, but their efforts will be fruitless. Something’s holding them back, a mysterious force whose mechanism we would find out three thousand years later is in the DNA of virtually every animal. And their offspring will be fruitless.
Kabbalah, Kilayim, and the Deep Structure of Speciation
For Darwin, the mule was a mystery that threatened the very logic of his theory of evolution. For the Torah, the mule is a violation of cosmic order. Today, genetics reveals that of the two, Torah was right. Nature is structured by boundaries between species.
The Torah’s paradigm—each kind according to its kind—is not just a religious belief or superstition. It is a radical insight into the architecture of life, one that modern science is only now beginning to appreciate. But Torah’s insight, unless it was a lucky coincidence, comes with other implications about nature that science cannot ignore.
Kabbalah says kilayim is part of the spiritual architecture of creation itself. Each species, each “kind,” is seen as a vessel for a unique divine energy or “power.” To mix species is, in the kabbalistic view, to uproot these powers from their proper place, disrupting the harmony and order of creation. So the nature “holds it back,” restrains it from the disorder it would create. Ramban said cross-breeding species was arrogant. It was as if Anah was saying the Almighty did a poor job, and he wanted to finish the task. Cross breeding undermines Creation itself.[6] Maybe that’s why the Talmud considers the idea that God created Anah’s mule on the last evening of Creation. On the one hand, it was a true miraculous innovation, like fire which was created that evening, but on the other hand it was too transgressive. [7] The prohibition of kilayim is a cosmic principle: the world’s diversity is not arbitrary, but a manifestation of distinct channels. When we respect these boundaries, we align ourselves with the inner order of the universe. When we violate them—whether by breeding mules or mixing wool and linen—we risk spiritual and ecological disorder.
But although the Bible beat science to the punch by three thousand years, its bigger view of nature is still dismissed by science. Science will not accept its assumption that the universe and everything in it was created by an intentional deity for a purpose. This is a profound axiom that separates the ways science and Torah think about how the cosmos works.As the t-shirt says, “God don’t make no junk!” Even though science was massively wrong about junk DNA, and wrong about species being kept separate, it is unlikely to change.
Science’s Maginot Line
Before it had the DNA evidence, evolutionary science was committed to an article of faith even when there was almost zero evidence for their belief: hybridization must occur. Now it has legitimate rationales for new beliefs: genetics enforces boundaries between species because it has evolutionary advantages. Of course hybridizing leads to sterility. It is too expensive. A donkey and a horse consume energy, grow, mate, carry a fetus to birth, etc.. and it is futile. The “hard stop” on hybridization is not a failure of evolution’s model, but a feature—a mechanical safeguard in DNA that maintains the resilience of a species. Evolutionary biology calls it “reinforcement of species boundaries.”
To me this sounds like a bit of circular reasoning (the fancy word is “tautology”):
Species don’t successfully hybridize because when they do they are unsuccessful.
Either way, the hard stop reframes Darwin’s and our entire scientific conception of how evolution works. Think of the 150 years science would have saved itself if it began with the assumption that species did have a self-conserving mechanism!
It invites us to imagine an alternate history of science. What if science had not split from religion in its two-century march from Francis Bacon to Darwin? What if it preserved as an alternate starting place Torah’s view of nature? The architecture of the universe has intricate integrity, unity, and a purpose. The whole structure depends on boundaries like kilayim. These boundaries have metaphysical origins but we may find they also have mechanical explanations, as with the DNA that enforces a species’ integrity. The two are not exclusive: We can explain the “hard stop”mechanically, but it also logically implies a purposeful vector – a teleology – in evolution. As Nobel Prize winners Albert Einstein, Bertrand Russel, Erwin Schrodinger, Ilya Prigogine and Roger Penrose have suggested,
There is no logically necessary contradiction between the fundamental beliefs of science – its a prioris – and the idea that the universe has a teleology, a purpose.[8]
This is not a call to abandon the methods of science. Knowledge still must be grounded in sensory or measurable data. Claims must be testable. We should still explain phenomena only by what chain of causes we know produced them, not why God wants it a certain way. Most modern scientists have the habit of deliberately excluding teleology. Not because it’s logically incoherent, but because it’s methodologically extraneous. Distracting.
This a deep historical and methodological tradition in science that for some is an article of faith. But it’s expensive and may be wrong. It’s like the Maginot Line which France built after WWI to prevent another German invasion. It cost billions of francs and dozens of years. It was largely useless once war came.
A New Paradigm for Science
We can imagine a new paradigm for science that completely overturns our approach to the universe by “turning the sock inside out.” What if science began with the goal of defining a vector – a purpose – for all things, instead of just trying to define its mechanics, a result of stuff, energy and coincidences? This view of nature sees it as dynamic and bounded. A boulder bounces wildly down a mountain. It looks like a chaos of tumbling but it really is following a glide path. There are places that it can go and places it cannot go and it has a certain destination.
Genes we once thought were junk have a “hard stop” that shows every individual of a species is in a feedback loop with the whole species to preserve its integrity. The baboon can’t mate successfully with a chimp because it costs the troop. Its DNA includes a mechanism to preserve the integrity of the whole species. Life is not just an endless blur of things bumping into each other, hoping that luck will produce a good outcome. The universe isn’t a Las Vegas casino. It’s a cruise ship heading somewhere. Boundaries and directions define a phenomenon as much its blind mechanics.
Let’s extend this model to see how it would work with two other of science’s enduring mysteries: life itself and consciousness.
Science offers no satisfactory explanation for how life began or how consciousness arises. What if we begin by assuming that both are “hard stops”? Instead of trying to punch through the barrier, we assume that the barrier is there for a reason. So what if it’s metaphysical? So is the assumption that everything is coincidental. Instead, science would look for the mechanisms of and reasons for the barrier. Nature just won’t let us build life from scratch or grow consciousness from the ground of brute supercomputation. We can specify the purpose of those boundaries once we discover the mechanistic explanations, just like with the hybrid problem, but we’d get there quicker. And if it confirms an old religious conviction – like kilayim – we might have to consider that there is a mystical unity and purpose in the natural world and everything in it.
In this new paradigm, scientists still don’t have to accept that these are boundaries created by a transcendent entity for a reason, but they may eventually come to the conclusion that that’s the most logical and efficient explanation.
David Porush
[1] “You shall observe My statutes: You shall not let your cattle [“kilayim“] mate with a different kind; you shall not sow your field with two kinds of seed; nor shall there come upon you a garment of cloth made of two kinds of stuff.” Leviticus 19:19, Deuteronomy 22:9–11
[2] Genesis 36:24
[3] Bereshit Rabbah 82:15
[4] The ENCODE (Encyclopedia of DNA Elements) Project was launched by the US National Human Genome Research Institute (NHGRI) in September 2003 as a follow-up to the Human Genome Project, with the aim of identifying all functional elements in the human genome. The ENCODE’s results, published in Nature and other journals in 2012, revealed that the vast majority of the human genome is absolutely not “junk” but has at least one specific purpose. This included specifying genes that enforce genetic boundaries. https://pmc.ncbi.nlm.nih.gov/articles/PMC3439153/; https://en.wikipedia.org/wiki/ENCODE ; https://pmc.ncbi.nlm.nih.gov/articles/PMC3438920/
[5] In house mice (Mus musculus) hybrid sterility is triggered by incompatibilities involving as few as two or three small chromosomes. These incompatibilities activate a genetic checkpoint during meiosis, preventing proper chromosome pairing and resulting in sterility, especially in hybrid males, enforcing the “hard stop” barrier. https://pmc.ncbi.nlm.nih.gov/articles/PMC11518865/ In fruit flies (Drosophila), decades of research have revealed that hybrid males often suffer sterility due to X-autosome incompatibilities. These findings have been extended to other animals, where chromosomal rearrangements and specific gene incompatibilities act as robust “hard stops” to gene flow between diverging species. https://journals.plos.org/plosgenetics/article%3Fid=10.1371/journal.pgen.1004088
[6] Ramban on Leviticus 19:19
[7] Pesachim 54a
[8] See also Michael Polanyi, Personal Knowledge (1958), Alfred North Whitehead Principia Mathematica (with Bertrand Russel, 1910-13), Thomas Nagel Mind and Cosmos (2012), Roger Penrose The Emperor’s New Mind (1989).
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