Go to the Nature Institute’s home page

Organisms and Their Evolution
A book by
Stephen L. Talbott

Chapter 19

Development Writ Large

book home page RSS Feed: RSS Feed for this page   

This is a preliminary draft of one chapter of a book-in-progress entitled, “Organisms and Their Evolution — Agency and Meaning in the Drama of Life”. This material is part of the Biology Worthy of Life project of The Nature Institute. Copyright 2022 by Stephen L. Talbott. All rights reserved. You may freely download this chapter for noncommercial, personal use, including classroom use.

Tags: development (ontogeny); evolution; evolution/and development

We have found throughout the preceding chapters that all biological activity, including at the molecular level, is thoroughly and irreducibly directive. Some biologists explicitly acknowledge the fact, and all biologists implicitly recognize it in their choice of descriptive language (see Chapter 2).

This leads naturally to the central conclusion of this book — a conclusion I will develop in this chapter — which is that we already know more than enough to say that evolution is a purposive, or directive, or telos-realizing, process. I understand that you may have difficulty coming to terms with this conclusion. But, as I hope to show, it is really just a matter of admitting to ourselves what we in fact know quite well. After all, an implicit recognition of the directiveness of living activity, however repressed, is the only thing that lends to the mass of biological description and theory any appearance of plausibility. Organisms just are beings that accomplish things, and those accomplishments are what biology is about.

The essence of this “unacknowledged knowledge” lies in the striking truth that living activities are quite unlike inanimate processes. Whether consciously or unconsciously, every organism directs its actions toward the future. At least, we experience the meaning and the time dimension of their actions that way. We can readily assume that most organisms themselves have no experience of aiming toward the future. But — and this is a crucial observation too easily ignored in evolutionary theorizing — there is a clear sense in which the objective character of their activity does exhibit what we cannot help seeing as a future-oriented meaning and directionality.

I try to clarify some of the issues surrounding all this in the book’s final chapter. But it has been both explicit and implicit throughout all the chapters that organisms are purposive beings, and the purposes are carried out with an incomprehensible wisdom and facility. A cell replicating its DNA, proceeding through division, and intricately coordinating its ever-changing patterns of gene expression; higher animals mating and providing for their young; a zygote undergoing all the “miraculous” transformations of embryonic development — these activities are, in terms of the prevailing principles of biological explanation, all but out of reach. Processes we conventionally accept as “causal” do not explain a developing organism’s living narrative — its ceaseless adjustment and coordination of causal activity so as to move directively toward a characteristic future that is not yet there.

But such telos-realizing narratives are also so “boringly” familiar that we cannot help taking them for granted. We assume their decisive role in every biological context we look at, and cannot “un-know” them even when we are theorizing from a position that ignores or denies them. And so we have the two sides of biology today: an uneasy, theoretical disregard of what seems ungraspable or dangerously mysterious, and a carefree, unexamined taking-for-granted of the powers so obviously at work in those all-too-familiar mysteries.

My aim in this chapter — an aim grounded in all the preceding chapters — is to facilitate the changed angle of vision that can enable the reader to grant full recognition to what is already known. I want to jog evolutionary thinking out of its customary pathways.

Evolution as a transformation
of developmental processes

No one will dispute that a wolf’s development, proceeding from a fertilized egg cell through embryonic and fetal stages to the pup’s birth, and then on through maturation to adulthood, is highly directive. It is an improvisationally coordinated, inherently meaningful, and adaptive movement embodying past results while oriented toward the future. It is part of an ever more complete self-expression. We would never say of a geyser or planet that it is, in this sense, moving toward fuller self-expression.

Yes, the organism’s development is a path full of unpredictable variation, never exactly repeated in different wolves. But this makes it all the more impressive that the entire trajectory remains persistently wolf-like despite all the adjustments to disturbances and despite all the adaptations to changing conditions — and also, despite the wolf’s feeding day after day on the flesh of other animals, which it never fails to convert into its own flesh. The individual wolf, embedded within its physical and social environment, exhibits the organizing power of its species, and is capable of negotiating a wolf-like path through the exigencies of life.

The three-week-old heart of the embryonic wolf is dramatically different from that of the six-week-old heart, which in turn differs from the heart immediately following birth (at about nine weeks), and this again differs from the heart of the mature wolf. It is presumably uncontroversial to say that any biologist who studies wolf physiology and development (something you can be assured I have never done myself) will expect the processes leading from one stage to another to show all the features of organic activity. Everything will prove thoroughly directive (telos-realizing), plastic, and adaptive, with earlier features serving as an effective preparation for later ones. Causation will be inescapably holistic, so that context-dependence will be a theme in all physiological, morphological, and behavioral explanation.

I doubt whether anyone would want to suggest that there are ways to get from the embryonic heart to the mature heart via any pathway not directive in the sense of all development.

But suppose we look at an evolutionary sequence, such as the classic textbook lineage of the horse. How might we imagine that a heart, structured that way fifty million years ago in the fox-sized horse ancestor, Hyracotherium, becomes this heart, structured this way in the Triple Crown winner, American Pharoah?

Can we realistically picture this evolutionary metamorphosis being achieved by processes fundamentally less well coordinated, less seamless and integral, or less consistent with the general character of all living activity, than the developmental transformations bridging the differences between, say, a two-month- and five-month-old horse embryo? Is there any fundamental difference in the nature of the developmental transformation achieved in the two cases? Is there any basis whatever for us to assume that the change of the heart at two stages of an evolutionary lineage is somehow less organically complex and less directive in character than the change in the heart at two stages of a single organism’s development?1

The fox-sized horse ancestor, <i>Hyracotherium</i>

Figure 19.1. An artist’s conception of the fox-sized horse ancestor, Hyracotherium (Eohippus).2

Triple Crown winner, American Pharoah

Figure 19.2. Triple Crown winner, American Pharoah.3

It is, after all, the whole nature of a developmental narrative to proceed directionally and seamlessly from here to there. It would require a powerful and unexpected set of arguments to show that nature, employing any conceivable set of historical processes, could effectively transform such a developmental narrative otherwise than by entering into and respecting the terms governing all such narratives. The need is to improvise as necessary while managing a frightfully complex, systematic, re-organizing, future-oriented activity that is the only basis for developmental transformation we have ever witnessed in organisms.

American Pharoah is as remarkable an endpoint for the evolutionary trajectory from Hyracotherium as it is for the developmental trajectory from its own zygotic stage. If we can hardly help taking for granted the directive activity required for the latter sort of development, can we find any justification for overlooking the necessity for directive activity in the former sort?

A thought experiment

Let’s assume that horse-racing enthusiasts never stop breeding horses. We’ll assume further that, having magically transported ourselves into the future, we are holding in our hands the exhaustive, generation-by-generation, molecular-level and phenotypic documentation for a thousand-year evolutionary lineage running from the 2015 Triple Crown winner, American Pharoah, to the greatest mega-champion of all time. Call him Chinese Ceasar if you wish.

It is a safe bet that Chinese Ceasar differs significantly from American Pharoah. The specific differences will depend, among other things, on the qualities that breeders valued throughout those thousand years — running speed presumably being one of them. Due to the principle of holism, through which a change in one feature of an organism is linked to change in many others, it is hard to imagine what sort of horse we would be looking at a thousand years from now. But surely it would be a horse of a different color.

Surely also, this would be a case of directed evolution — “directed”, not merely in the sense of “channeled in part by environmental and developmental constraints”, but also “resulting from intentional agency”. After all, the entire line of descent would have been intended by breeders and their ideals. But would we recognize this fact if we were unaware of the breeders’ role? That is, could we discover, solely from the horse lineage itself, the fact that it progressively realized certain ideas, or guiding principles, or intentions?

The question seems to me important. Strongly held opinion has it that actual evolutionary history shows no directive or progressive aspect — not, at least, in an intentional sense bearing much resemblance to the directionality imposed by breeders. But if the answer to our question is, “No, we wouldn’t necessarily be able to recognize Chinese Ceasar as the result of directive evolution” — if, in fact, we have not yet learned to distinguish the features of a directive evolutionary lineage from those of a non-directive one — then on what grounds can anyone claim that normal evolution is not directive?

If I am not mistaken, then, here is a fair request we can make of evolutionary theorists. Show us how we might distinguish, at least in principle and in the metamorphosing organisms themselves, a non-directive evolutionary process from a directive one. Or, if they cannot do this, let them explain the evidence upon which they conclude that evolution is, in general, nondirectve.

skeleton of Hyracotherium

Figure 19.3. A museum skeleton of Hyracotherium.4

skeleton of a modern horse

Figure 19.4. Skeleton of a modern horse. The two images are not shown at the same scale. The horse skeleton is several times larger than the ancestral skeleton.5

Experiment concluded?

As it happens, a year or so after I first wrote the preceding section, I discovered that philosopher Daniel Dennett had already pursued the same thought experiment — and had received an answer. He pictured aliens visiting earth and tampering with natural selection for a while, then departing. He asked: “Would their handiwork be detectable by any imaginable analysis by biologists today?”

Dennett did the sensible thing: he consulted some biologists. “All the biologists I have queried on this point have agreed with me that there are no sure marks of natural, as opposed to artificial, selection” (Dennett 1995, pp. 316-19).

This is a dramatic acknowledgment, although the real significance of it seems to have escaped Dennett. He was clearly thinking of intelligent design when writing this passage, and feared that ID advocates might seize on the idea that you can’t disprove the intervention of an external Designer in evolutionary history. So he was quick to reply that, barring discovery of a feature positively requiring a Designer’s intervention — a feature that natural selection without a Designer could not explain — there was no refutation of Darwinism to be had here.

If you want a measure of how thoroughly the organism has dropped out of sight in today’s evolutionary theory, Dennett’s account offers it. Apparently it did not even occur to him to ask, not about an intelligent Designer, but about organisms themselves, whose powers of directive development, physiology, and behavior, displayed right before our eyes, constitute their entire life story. The question, still ignored today, is how the organism’s living activity participates, out of its own purposive, cognitive, and intentional nature, in the broader intentional coherence displayed so clearly in evolving populations.

To be as unambiguous as possible: the question here is not about an external designer, but about a purposiveness inherent in populations of organisms analogous to the purposiveness we see playing through the many more or less independent cells within an individual body. And the question is hardly out of bounds, given biologists’ apparent agreement that “there are no sure marks of natural, as opposed to artificial, selection”. One wonders how it is that the idea of meaningfully directive evolution has been so scorned if in fact all biological processes we can directly observe are irreducibly directive, and if we have no ready means for distinguishing a non-directive evolution from a directive evolution — or even from an artificially directive evolution.

You might think that the point could be reversed. We could ask, “How can anyone scorn the idea of non-directive evolution if in fact we have no ready means for distinguishing non-directive from directive evolution?”

But it is part of my present argument that there is good reason why we cannot point to a distinction between the two forms of evolution. It is impossible to imagine in any coherent fashion an evolutionary-developmental process that is not subject to the guiding principles or ideas inherent in the form progressively being realized. So the only thing biologists are ever in fact thinking of is directive evolution, whether they have acknowledged it to themselves or not.

The wisely purposive lives of organisms — their striving for life and survival, the intricate wonders of their capacity to reproduce, their masterful ability to gather and organize a unified, workable inheritance for their offspring — these “miracles” of directive activity (in terms of which, as we have seen, natural selection is defined) are so thoroughly imprinted upon our experience that not even an entrenched scientific materialism can dislodge them as implicit assumptions of our evolutionary theorizing.

So it is not that we have a choice between directive and non-directive evolution. The only biological activity we ever see or can consistently imagine at any scale is directive activity.

It is, in the primary sense,
populations that evolve,
not individual organisms

The potential shapes and functions of proteins are virtually infinite. So a major question in evolutionary studies has been, “How, amid this vast landscape of possibility, can more or less random mutations in DNA lead, in any reasonable amount of time, to the particular proteins useful for an organism’s current adaptive needs?” This question has been a flashpoint for debate between intelligent design advocates and conventional biologists. The debate is, to say the least, perplexing. That’s because the foundational assumption on both sides — that natural biological processes are inherently non-directive — is so dreadfully wrong.

The relevant fact is that nothing in an organism escapes being caught up in meaningful and directive processes. There is simply no available context for talk of “random” mutations. The processes of DNA maintenance, replication, damage repair, and mutational change are among the most fully characterized and the most intricately purposive and directive activities we have so far explored at the molecular level. DNA damage repair and the closely related incorporation of mutational change are, perhaps, orders of magnitude more complex than the spliceosomal activity we looked at in Chapter 8. It takes place in the same fluid environment as RNA splicing. And there is the same play of organizing ideas and ideal reasons for what goes on — reasons of a sort that cannot be derived from concepts of physical lawfulness.

At this point — without ever addressing the decisive problem of the rational coherence of molecular activity in the cell — evolutionary theorists are quick to tell us that, although genetic mutations are in general nonrandom, they are nevertheless crucially random in one regard:

Mutations are claimed to be random in respect to their effect on the fitness of the organism carrying them. That is, any given mutation is expected to occur with the same frequency under conditions in which this mutation confers an advantage on the organism carrying it, as under conditions in which this mutation confers no advantage or is deleterious (Graur 2008).

So then another debate arises: “Are mutations really random relative to their benefit for the organism, or are they ‘directed’?” This is where the question of purposiveness or direction in evolution is thought to come to a sharp focus. The effort to prove or disprove the existence of “directed mutations” is often pursued as if it would tell us about the directiveness of evolution.

The question about mutations in the individual organism is certainly significant and worth pursuing. But here, too, the underlying assumption of most debate makes little sense. If we are talking about a telos-realizing evolutionary process, then the question is not about a mutation’s benefit for the individual organism, but rather about its relation to whatever is being realized in the overall evolutionary process. We are not helped much in this by making assumptions about the relation between mutations and individual fitness. Rather, we must investigate how the individual organism is caught up in, and participates in, directive processes involving populations, species, and even larger groupings.

This is much the same as with individual development. We recognize the meaningful path of development, not merely by looking at what happens to an individual cell, but by picturing the coordinated activity of all the cells in the body. Any individual cell, or group of cells, may, as we saw in the introduction to Chapter 18, be caught up in a coordinated dying-off process essential to the formation, say, of a particular organ. It is not, primarily, the welfare or fate of individual cells we are interested in, but the larger developmental transformation. Or: we are interested in the individual cell because of the way it participates in, and is informed by, that larger movement.

But the evolutionary parallel here requires some explanation.

Far from a simple, linear process

We know that individual development is marked by more or less dramatic periods of especially rapid, intense transformation. In our own development, profound changes occur around the time when the young child is taking its first steps and speaking its first words. Likewise with puberty and menopause. Then, too, there is the entire, nine-month period of human embryological development, from the zygote onward. This pre-natal phase is marked by vastly more physiological and morphological change than occurs throughout all the subsequent decades of life.

Perhaps even more dramatic are the many millions of species — for example, among insects and amphibians — that undergo one or another kind of metamorphosis. A worm becomes a butterfly, a tadpole transforms into a frog. This reorganization can be both swift and virtually total. (See the description of insect metamorphosis in Chapter 17.) But such times of emphatic change typically occur between extended periods of relative stasis, or slower change.

That a similar pattern often, but not always, holds in evolution was argued in 1972 by paleontologists Niles Eldredge and Stephen Jay Gould, who called the pattern “punctuated equilibrium”. Since then various forms of the idea have been broadly accepted, so that another prominent paleontologist, Robert Carroll, could write of vertebrate evolution that “instead of new families, orders, and classes evolving from one another over long periods of time, most had attained their most distinctive characteristics when they first appeared in the fossil record and have retained this basic pattern for the remainder of their duration” (Carroll 1997, p. 167).

It’s not just the relative suddenness of change that matters in the present context. More significant is the remarkably nonlinear character of the processes by which major evolutionary innovations occur. My colleague, the whole-organism biologist Craig Holdrege (to whom I am deeply indebted for many of the insights in this section),6 has drawn attention to one of the central lessons emerging from paleontological work: when something dramatically new arises in the fossil record, it is typically foreshadowed by fragmentary “premonitions” (not his word) in various taxonomic groups, some of which may then go extinct. There is no smooth, continuous, single line of development leading to the new form, which may arise not only rather suddenly, but also as a novel synthesis and transformation of the earlier, scattered, premonitory gestures.

Holdrege shows this very clearly in his book chapter on the frog (“Do Frogs Come from Tadpoles?”).7 After mentioning that no frog fossils have come to light from before the Jurassic period of the Mesozoic era, he notes that “the first frog fossils have virtually the same proportions and the same skeletal morphology as today’s frogs”. Earlier, there were indeed rare transitional forms possessing some frog features, especially features of the head. These were “a far cry from frogs, but if you know frog morphology well, you can see hints of what is to come”. He goes on to say of the paleontological record that

the hints or foreshadowing of what will come later are not manifest in only one type of fossil, but in several. Various elements of what appears later in the new group are manifest in earlier periods, but in different lineages. Evolutionary scientists often speak in this connection of “mosaic” evolution, since various characteristics appear in different arrangements in different organisms … Even when a trove of fossils is available, such as in the horse family (Equidae), it is not the case that they line up in a neat series. Rather, there is surprising diversity in the forms that predate modern horses (Holdrege 2021, p. 249).

In some of his other work Holdrege has pointed to the same reality in the human and pre-human fossil record. Using accurate models or professional drawings of the available skulls, done to scale, he asks students to arrange them in an order showing an apparent progressive movement toward the human form. It can be an informative (if frustrating) exercise, since no definitive sequence emerges. One skull may show a seemingly more “advanced” feature than the other skulls, while at the same time showing more “primitive” ones (Holdrege 2017).

All this resonates with other facts that have been in the news these past few years — news bearing on the most recent human evolution. We have heard a good deal about cross-breeding between humans, Neanderthals, and Denisovans, and also about the prevalence of variation within populations. The genomes of a major part of the present human race contain a significant proportion of Neanderthal and/or Denisovan DNA, and these elements are thought to play significant roles in human biology.

cichlid fish (Pundamilia (Haplochromis) nyererei)

Figure 19.5. A cichlid fish (Pundamilia [Haplochromis] nyererei), one of hundreds of cichlid species in the lake region of eastern Africa.8

Then, too, there is the broader fact that hybridization between species and genera — and even between families — is now linked to rapid evolutionary change. One impressive story was reported in the journal Science, in an article titled “Hybrids Spawned Lake Victoria’s Rich Fish Diversity”. Among cichlid fish in Africa’s Lake Victoria, the rate and extraordinary extent of diversification has, we’re told, “baffled biologists for decades”. A mere 15,000 years ago there were only a few ancestral species, whereas today — as a result of a remarkable “adaptive radiation” — 500 or so species exist. Some of them “nibble plants; others feed on invertebrates; big ones feast on other fish; lake bottom lovers consume detritus”. Varying in length from a few centimeters to about 30 centimeters, they “come in an array of shapes, colors, and patterns; and dwell in different parts of the lake”.

The report goes on:

Now, researchers have evidence that ancient dallying between species from two watersheds led to very genetically diverse hybrids that could adapt in many ways to a new life in this lake. Increasing evidence has shown that hybridization, once considered detrimental, can boost a species’s evolutionary potential. Suspecting that might be the case in these fish, researchers sequenced hundreds of cichlid genomes, built family trees, and compared the genomes of fish throughout that part of Africa. They discovered that parts of cichlid genomes have been mixed and matched in different ways through time, with various descendants being repeatedly separated and reunited as lakes and rivers dry up and refill. These hybrids had extensive genetic diversity that fueled rapid speciation (Pennisi 2018).

And even more radical than hybridization has been the dramatic, endosymbiotic origin of different life forms at the cellular level. This has yielded some of the most decisive evolutionary transitions of all time. For example, the presence of chloroplasts (in plant cells), mitochondria (in animal cells), and perhaps a number of other cellular organelles, including possibly the eukaryotic cell nucleus — are now thought to have resulted from the merger of very different life forms. That is, a once free-living, single-celled organism becomes permanently internalized as a functioning part of a different (host) single-celled organism.

It took a long time for biologists to accept theories of endosymbiosis, which were first put forward more than a hundred years ago. This is hardly surprising because of the seemingly insuperable nature of the problem: once joined together, the two cells, with their entirely different life cycles, would have to proceed harmoniously through all the necessary and diverse functions of the new, united entity, including cell division. So it seemed that a successful merger of two very different organisms would have required an almost unthinkable and well-directed sort of “management” by both the host organism, and the internalized one. But the truth appears to be that, at critical moments in evolutionary history, such powers were indeed exercised.

Still further, we should not forget the broad fact of horizontal gene transfer — that is, the movement of genetic material laterally between different kinds of organisms rather than vertically through inheritance from biological parents. This movement is often mediated by bacteria or other microorganisms, and can involve the transmission of genes between widely differing organisms. Where this gene mixing occurs — and it is known to have occurred extensively, especially in simpler life forms — it throws a wrench into all theorizing about slow, linear, evolutionary change based on random mutations passed down from parent to offspring.

As if that were not enough, we have to reckon with the major role viruses have played in shaping many genomes, including those of mammals. For example, every human genome is thought to contain several times as much DNA of viral origin than the DNA of all the protein-coding genes combined.

Then again, there is the entire mass of microorganisms comprising the microbiomes of humans and other organisms. The collective genetic content of the human microbiome rivals that of our own genomes in total mass, while also being functionally crucial for our lives.

A sprawling narrative

So you get the picture. Traditional questions about “directed mutations”, their effect upon the evolutionary “fitness” of individual organisms, and their spread through a single population via “normal” genetic inheritance — these have been rendered less relevant by our growing knowledge of actual evolutionary processes. We need to raise our sight to the larger collective sphere in which profound and relatively rapid evolutionary change can occur — the sphere where we can discover the kind of unexpected synthesis of diverse and scattered potentials described above.

Within this larger sphere, one thing we can truthfully say about mutations (or the creation of genetic variation) is that they can be healthy for the species. They provide resilience in the face of changing environments. This is true regardless of any “fitness or evolutionary benefit” for the individual. And it is, of course, the species as a whole, not just the individual organism, that is evolving. But not only the species. There are (as we have seen) diverse interactions of many sorts among different groups of organisms, resulting in the movement of both genetic and non-genetic material between individuals, populations, species, and higher-level groups.

And so we arrive at an extraordinarily complex picture. A “strange dalliance”, a few Neanderthal genes here and Denisovan genes there, the hidden and genetically seething world of microorganisms and symbionts constituting a vital part of the substance of higher organisms, the wholesale, lateral exchange of genetic resources among lower organisms, the thriving of some lineages and the extinction of others that nevertheless carried for a time part of the essential “mosaic” of evolutionary potentials, and, finally, the relatively sudden convergence, or synthesis (evolutionary metamorphosis), of all those potentials in a new evolutionary configuration — well, if you want to ask about the directiveness of evolution, then all this, along with the overarching agency so clearly recognizable both in the outcome and in the only conceivable path of coordination for getting there, is the relevant stuff of your question. We are not looking at the isolated matter of a mutation’s fitness for an individual organism.

One thing is certain: we see no lack of room for a play of intentional, coordinating activity in evolution, just as we see a play of developmental intention through all the cells of, say, a mammal’s body. And in both cases it is the result of the activity, together with the necessarily coordinated, adaptive nature of the entire process for getting there, that tells us a directive and purposive activity has been going on.

Our current ability actually to trace this directive activity in evolution may be rather poor, if only because the fossil record tells us so little about the sprawling evolutionary interactions we know must have occurred. But we do know that the development of the individual horse, American Pharoah, required all the familiar, directive powers we have observed in developmental biology generally, all the intricate coordination, adaptation, and compensatory adjustment to disturbances, all the evident wisdom, thoughtfulness, and well-directed intention.

And we also know that much more than the wisdom of individual development was required for the evolutionary transformation of Hyracotherium into American Pharoah. For not only was it necessary for every ancestral animal in the relevant lineages to be capable of undergoing its own development, but so, too, the relations between mates and between predators and prey, together with all the other “complications” hinted at above, had to come under a directive, coordinating agency capable of realizing all the various metamorphoses of interacting lineages along the way.

All this is decisive to acknowledge in a forthright spirit. However much we may not yet understand, we see the fact of this kind of directive evolutionary metamorphosis in the picture already given to us.

Where are we now?

Evolution As a Form of Development

We have been led by all the preceding chapters to this present one, in which we have concluded that the question of the directiveness of evolution turns out to be almost trivially simple, with an unproblematic answer: evolutionary “development” must be at least as directive as the development and life processes of an individual organism.

Their ignoring of the fundamental reality of directiveness in the life of organisms is a central reason why biologists have, for decades, denied all possibility of a coherent telos-realizing aspect of evolution. This emphatic denial has taken hold despite their inability consistently to imagine a non-directive form of evolution, and despite their admission that they have no criteria for distinguishing a directive from a non-directive form.

The fact is that no one can avoid assuming the organism’s thorough-going directiveness, because it is just too obvious. And that inescapable assumption, whether or not acknowledged, is why it is impossible to imagine a non-directive form of evolution distinct from a directive one. The effort would be like trying to imagine an evolution of stones. The intention to formulate such a view of evolution is always undercut by one’s awareness of the actual nature of organisms, as revealed in the development, physiology, and behavior of animals.

We have also seen in this chapter that the coordinating agency at work in evolution cannot be centered in the individual organism, but must play through complex interactions among many organisms and populations. We have noted a distinctly nonlinear aspect of much of evolution, where foreshadowings of changes to come (“glimpses of the future”) can be found scattered through diverse lineages, leading, at certain critical points, to a more or less dramatic and sudden reconfiguration and synthesis of much that had gone before. This reconfiguration can involve hybridization, lateral gene transfer, and symbioses, among other things, in addition to the predatorial, mating, and migratory activities that have long figured centrally in evolutionary theorizing.

All this means that the relation between a mutation and the individual fitness of an organism is no more central to the origin of species than the “fitness” of an individual cell is central to the development of a complex organism’s adult form. In fact, the death of many cells may at some point constitute their positive contribution to the adult form. Similarly, the coordinated patterns of life and death within evolving populations can be recognized as essential to evolution.

In general, we have seen that the directive processes of evolution present us with no fundamental problems of purposiveness and agency that have not already been presented to us by the directive processes of development. Purposiveness and agency are definitive givens of biology, and their denial destroys biology as an independent science of life.

But while this chapter, building on the preceding ones, sets forth my positive argument for acknowledging the essential directiveness of evolutionary processes, the discussion nevertheless remains incomplete. We have yet to look at the way whole organisms and whole-organism inheritance have been effectively negated or rendered invisible by the almost universal preoccupation with genes at the foundation of evolutionary theory. We take this up, along with questions about inheritance and about the “disreputable” topic of holism, in our next three chapters.


1. The most obvious difference between individual development and evolutionary development is that coordination in the latter case must play, not through the countless cells in a single organism, but rather the countless individuals in various populations. We considered this difference in Chapter 18. But see also below on the nature of evolutionary transformation.

2. Figure 19.1 credit: Anonymous (CC BY-SA 4.0).

3. Figure 19.2 credit: Coolmore photo.

4. Figure 19.3 credit: Ghedoghedo (CC BY-SA 3.0).

5. Figure 19.4 credit: Wellcome Images (CC BY-SA 4.0).

6. I also owe a good deal of my understanding of evolution in general to the writings and lectures of Holdrege, as well as to personal conversations with him. See especially his chapters on the giraffe and the frog in Seeing the Animal Whole — And Why It Matters (2021).

7. Holdrege 2021, pp. 213-56. Holdrege’s answer to the question, “Do frogs come from tadpoles?” is, in a very important sense, “no”. The appearance of the frog represents the achievement of something new, not the mere “rolling forward” of fully determinative “mechanisms” already present in the tadpole. Upon seeing a tadpole for the first time, we could not predict the existence of the forthcoming frog, as if it were a physical necessity.

8. Figure 19.5 credit: Kevin Bauman (CC BY-1.0).

Tags: development (ontogeny); evolution; evolution/and development


Dennett, Daniel C. (1995). Darwin’s Dangerous Idea: Evolution and the Meanings of Life. New York: Simon and Schuster.

Graur, Dan (2008). “Single-Base Mutation”, Wiley Online Library, eLS. doi:10.1002/9780470015902.a0005093.pub2

Carroll, Robert L. (1997). Patterns and Processes of Vertebrate Evolution. Cambridge UK: Cambridge University Press.

Pennisi, Elizabeth (2018). “Hybrids Spawned Lake Victoria’s Rich Fish Diversity”, Science vol. 361, no. 6402 (August 10), p. 539. https://science.sciencemag.org/content/361/6402/539

Holdrege, Craig (2017). Diversity in Human Fossil History — A Teaching Unit on Hominid Evolution. https://www.natureinstitute.org/book/craig-holdrege/diversity-in-human-fossil-history/about

Holdrege, Craig (2021). Seeing the Animal Whole — And Why It Matters. Great Barrington MA: Lindisfarne.

Mayr, Ernst (1961a). “Cause and Effect in Biology”, Science vol. 134, no. 3489 (November 10), pp. 1501-6. Available at https://www.jstor.org/stable/1707986

Popov, Igor (2008). “Orthogenesis Versus Darwinism: The Russian Case”, Revue d’histoire des sciences vol. 61, no. 2, pp. 367-97. https://www.cairn.info/revue-d-histoire-des-sciences-2008-2-page-367.htm

This document: https://bwo.life/bk/devo_l.htm

Steve Talbott :: Development Writ Large