Max Telford’s new book, The Tree of Life: Solving Science’s Greatest Puzzle, was a welcome read for me, as the Tree of Life concept has long been an area of personal interest. Telford is a professor at the University College London in Genetics, Evolution & Environment. My praise for the book surrounds its easy readability, its entertaining stories, and its explanation of some of the biggest challenges in “tree of life” research. My two critiques are that the book downplays how serious some of the problems in the field actually are, and it consistently treats common descent as the only viable hypothesis without serious consideration of alternatives.
I’ll be reviewing this book topically, beginning with the beauty and importance of classification and ending with the implications of belief in the tree of life.
The Beauty and Importance of Classification
Early in the book, Telford quotes Tim Ingold (via Tindell Hopwood): “The urge to classify is a human instinct; like the predisposition to sin, it accompanies us into the world at birth and stays with us to the end.” Indeed biologist Carol Kaesuk Yoon has noted the growing tension between this innate human desire to classify and the predictions of evolutionary biology (Yoon 2010). Humans have always grouped organisms by shared characteristics, and that basic practice long predates Darwin. The greatest systematist in history, Carl Linnaeus, lived before Darwin and produced an impressive hierarchical classification system based on the belief that similarities derive from shared archetypal patterns in the mind of the designer.
In exploring the importance of classification it is helpful to think about the reason humans classify other things. Starting as children we classify Matchbox cars, trading cards, Barbie outfits, etc., all with a functional reason in mind. Classification happens around shared characters that have a function in one context but not another. A race car is useful for speed; a bulldozer is suited for moving dirt. A miniskirt works for a party; jeans are better for riding horses. These categories are organized by function: what something does and how it is used.
I recently discussed this issue in a post about CRISPR classification, here. My critique was simple: classification sometimes needs to reflect intended use. If the downstream goal is genetic engineering, then grouping CRISPR systems by functional properties may be more informative than grouping by supposed genealogical ancestry.
Telford provides a vivid example of different classification outcomes depending on method. He notes that the Tasmanian wolf closely resembles a dog, yet we “know for sure that Tasmanian wolves are far from being close relatives of the dog family. […] The Tasmanian wolf is in fact a marsupial, as is most evident from its possession of a pouch for carrying young. It is (was) a relative of kangaroos, quolls, and koalas.” While I understand the phylogenetic classification that places the Tasmanian wolf (thylacine) within the marsupial lineage, this classification might not be helpful depending on the purpose. For example, a zookeeper relying solely on this system might house the thylacine with kangaroos and koalas (as fellow marsupials), where the end result would be fewer exhibited species at the zoo!
Or take this example, on p. 43, Telford notes, “The coelacanth, while undoubtedly a fish, is more closely related to a human than to a goldfish (which lacks these fin bones).” If this grouping led to a functional implication of implied similar habitats or lifestyles, the coelacanth would certainly protest being grouped with land-dwelling humans rather than its fellow water-bound fish like the goldfish.
These examples hint at some of the tension between the field of taxonomy and the field of phylogenetics. Humans tend to classify based on function, while phylogenetic approaches (attempting to trace genealogical ancestry) classify based on amino acid or nucleotide similarity for specific genes, which are thought to represent closeness of genealogical relatedness.
In summary, the ability to classify is a natural part of being human and it helps us group objects based on how we might use them. Tracing genealogical ancestry is also important, but not the same thing. Today we use it for forensic analysis to solve crimes or as Telford discusses, to infer evolutionary history.
A Flawed Assumption
Telford also offers a flawed assumption — namely that the universal genetic code and universal genes constitute proof that everything alive today arose from a common ancestor. He states, “A universal gene, homologous in every single living organism, points to a common ancestor of all life and one that is very, very old indeed (p. 85).” On p. 90 he writes, “One extraordinary truth revealed by Darwin’s theory of evolution is that relationships between species imply the existence of ancestors.” Again, on p. 92: “The exact same genetic code together constitutes the most persuasive proof possible that everything alive today arose from one single origin.”
But wait — is the near-universal (Ewert 2024) genetic code and the presence of certain shared genes truly compelling evidence for common ancestry? Isn’t this reasoning akin to claiming that since all cars use rubber tires, this shared feature proves they evolved gradually through a blind, unguided process ages ago? Moreover, doesn’t this argument rest on assumptions about how a designer might operate? (The Science Dilemma 2025)
Here’s a clue. Telford admits there are non-genetic examples of “evolution” (“evolution” here is more precisely understood as “nested hierarchy”). He notes on p. 248: “Possibly the most famous example of non-genetic evolution can be found in human culture. We can reconstruct trees relating languages, and individual words and the books that contain them. We can also use trees to represent the histories of other parts of culture: arts and crafts, customs, laws, religions, technology, recipes, and designs.”
Hold up a minute. Telford is acknowledging that nested hierarchies or “evolution” arise from non-genetic processes and can be represented by tree structures. Yet, he is also asserting that the genetic nested hierarchy we observe in living organisms constitutes definitive proof that “everything alive today arose from one single origin” (p. 92). Therein lies a logical problem.
Telford is asserting the presence of nested hierarchy as strong/unique evidence for unguided common descent, while simultaneously acknowledging that the same pattern can arise from intentional design. If a pattern (a nested hierarchy) can arise from two origins (evolution and design), its mere existence cannot logically “prove” either of the hypotheses.
Maybe my critic would say, “Wait Emily, you are making a fallacy of equivocation! The examples of nested hierarchies from non-genetic ‘evolution,’ such as language, are in some sense artificial. The biological hierarchies are real — evidenced by the fact that they are deep and have agreement across independent datasets.”While I agree there is subtlety worth unpacking, my initial response is that Telford’s book doesn’t even express an awareness of the contradiction here — namely that he acknowledges that intelligent agents can produce the kinds of patterns of similarity that result in nested hierarchies, and yet won’t even consider the possibility that this could be happening in biology. To put it another way, he takes the kind of evidence that indicates common design in the technological realm (a nested hierarchy) and calls it proof of unguided common ancestry in the biological realm.
That said, let’s look a little more closely at possible differences in predictions the evolution and design hypotheses make.
- Descent with modification from a common ancestor (evolutionary hypothesis): Similarity is expected because organisms inherit shared features from genealogical ancestry, with differences accumulating through divergence.
- Independent origins where there is no genealogical connection above the family level (design hypothesis): Similarity and difference are both anticipated whenever they serve functional or engineering constraints for the organism, or aesthetic purposes of the designer.
Under the design view, we would generally expect functional reuse of components when it converges to the optimal solution given the organism’s design requirements, while under evolution we would expect similarity to reflect historical contingency and inheritance rather than optimality. That said, exceptions are possible in both cases. A designer might reuse a solution arbitrarily or for non-functional reasons (e.g., stylistic consistency, economy, or simplicity). Also, evolution is said to produce similarities when the same selective pressures favor the same solution independently. Since both hypotheses make similar predictions about the patterns, the mere presence of nested hierarchies, or conserved genes, or the mostly universal genetic code does not decisively favor one explanation over the other.
Thus, Telford leads us to a key result:
Any set of objects can be arranged into a tree — even when common descent via a genealogical relationship did not exist. You can build a tree for any collection of items, complete with a single trunk representing a common origin. Such “trees” have been made for things we know did not evolve: shirts, shoes, cars, mobile phones, languages, etc. Therefore the mere existence of a tree diagram does not distinguish between two very different explanations:
- descent with modification from a common ancestor, or
- independent origins at some level (maybe family?) with no genealogical connection.
The real scientific question is not “Can we draw a tree?” but rather:
- How well do the characters actually fit a single tree?
- How many characters conflict with the tree pattern?
- What independent evidence exists that could tell us whether the tree reflects true genealogical descent or something else?
What are the implications of this key result? While common descent is certainly a possibility in many cases, it means that the case for common descent is often overstated. Telford writes on p. 110: “The only sensible explanation for all these amazing coincidences […] is that both the genes themselves and the jobs that they do must have been inherited by both mice and flies from their common ancestor, Urbilateria.” Again on p. 146 “This changed version of the nad5 protein is found only in this group of animals, and it stands as clear proof that they are all related to one another.”
These statements are unsubstantiated in their present form. They present common descent as the sole reasonable explanation for similarity while dismissing alternatives without justification. In particular, they do not address the possibility that these regions of similarity could reflect functional necessity.
Bottom line: The nearly universal genetic code does not constitute proof that everything alive today arose from a common ancestor. A similarity does not constitute proof that two things are genealogically related.