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Evolutionary Progress

2750 words

Phylogeny-reading is hard for some. So hard that there are numerous papers in the literature that correct many students’ misunderstandings that come along with reading these trees (eg Crisp and Cook, 2004 Baum, Smith, and Donovan, 2005; Gregory, 2008; Omland, Cook, and Crisp, 2008). Some may read certain trees as showing a type of “evolutionary progress” in the history of live, from “primitive” to more “advanced” life forms. Notions of “progress”—both in society and evolution—still continue even to this day (see Bowler, 2021 for a great discussion). That if one hasn’t “branched” on the tree, they are then “less evolved” than organisms that “branched more.” This is illustrated wonderfully by PumpkinPerson’s misunderstanding where he claims:

If you’re the first branch, and you don’t do anymore branching, then you are less evolved than higher branches

This conceptual confusion comes from his idea that more branching = more evolution, therefore more branching equals “more evolved” organisms. But, unless an organisms is extinct, all organisms have evolved for the same amount of time, so this defeats his claim here.

Such fantastical claims of “evolutionary progress”, in humans, come from JP Rushton who, although he didn’t explicitly state it (Lynn did), Rushton (1997: 293) said he “had alluded to similar ideas in previous writings.” But Rushton (1992) was more explicit—he said that “One theoretical possibility is that evolution is progressive and that some populations are more “advanced” than others.” This is in reference to his long-debunked theory that Asians are more K-selected than whites who are more K-selected than blacks, dubbed “r/K selection theory” or “Differential K theory.” But I’m not aware of Rushton wrongly inferring this from tree-reading, that’s a PP thing.

So Rushton, like PP, assumed that those groups that emerged after older groups are more “evolutionarily advanced” than others. But, although Rushton has a few editions of his book after the publication of Gould’s (1996) Full House where he refutes the claim that evolution is “progressive”, Rushton is strangely silent on the matter. In any case, any form of “progress” to evolution—if it did exist—would be upended by decimations leading toward species extinction.

Progressionists think that evolution is both directional and, obviously, progressive. That is, there seems to be a goal to get more and more complex, or at least a bigger body size, and that this is “good.” But there seems to be a kind of inherent, unspoken of “value” one has to attach to views about “evolutionary progress.” For instance, Bonner (2015: 1187) states that “If we look at evolution from a great distance, we see a progression.” For example, see Bonner’s (2019) Figure 1 where he shows an apparent increase in body size which can be said to be “progression.” This can, though, be explained passively, that is, explained by a non-directedness for body size in evolution as Gould (2011: 162), using his drunkard’s walk analogy writes (Gould’s emphasis):

Given these three conditions, we note an increase in size of the largest species only because founding species start at the left wall, and the range of size can therefore expand in only one direction. Size of the most common species (the modal decade) never changes, and descendants show no bias for arising at larger sizes than ancestors. But, during each act, the range of size expands in the only open direction by increase in the total number of species, a few of which (and only a few) become larger (while none can penetrate the left wall and get smaller). We can say only this for Cope’s Rule: in cases with boundary conditions like the three listed above, extreme achievements in body size will move away from initial values near walls. Size increase, in other words, is really random evolution away from small size, not directed evolution toward large size.

Such notions of “evolutionary progress” do date back to Aristotle, as Rushton rightly notes, who classified “lower” and “higher” organisms. The modern view of the scala naturae is that there is a steady line from less complex to more complex organisms, with humans at or near the end. Bonner, in his 1988 book, does argue for “higher or lower” species, but in his newer 2013 Randomness in Evolution he argues that evolutionary change is mostly passive or non-driven. Rushton (1997: 294) cites Bonner (1988: 6) saying that it is acceptable to use the terms “higher” and “lower” organisms. But Diogo et al (2013: 16) write:

There are two main problems with this latter statement. Firstly, there are many examples of how older animals (from
‘lower’ strata) are often considered, in various aspects of their biology and physiology, more complex than more recent ‘higher’ animals (from ‘higher’ strata). … Secondly, and perhaps more important in the context of the present review, in the original idea of scala naturae the term ‘higher’ taxa referred to humans and to the animals that are anatomically more similar to humans, and this is still the way in which this term is used by many authors nowadays (reviewed by Diogo & Wood, 2012a, 2013)

Although humans went through more transitions than other primates, this did not result in more muscles than in other primates and that “there is effectively no general trend to increase the number of muscles at the nodes leading to hominoids and to modern humans” (Diogo et al, 2013: 18). Thus, using the tortured logic of progressionists, humans are less evolved than other primates.

Using PP’s tortured logic on tree-reading, I asked him “Who is more evolved?” in the following tree from Strassert et al (2021):

PP then says that “new research inspires fresh look at evolutionary progress.” But some confusions from PP must first be noted. He “predicted” Amorphea to be “less evolved” than Diaphoretickes; but humans are in Amorphea, therefore humans—to PP—are less evolved than plants. PP then said that Wiki says that Amorphea is “unranked”—but all “unranked” means here is that the classification is not a part of the traditional Linnean taxonomy. PP likes his simpler trees where he can get the “conclusion” that he hopes for—that there are more and less evolved organisms which conform to his a priori biases on the nature of evolution. He then said that Amorphea does not appear to be a widely recognized taxon… but it has been noted that “Amorphea is robustly supported in most phylogenomic analyses” (Burki et al, 2019: 7) while Amorphea and Diaphoretickes form two Domains in Eukaryotes (Adl et al, 2019). So, it seems, Amorphea IS a widely-accepted accepted supergroup.

The philosopher of biology and mind Jianhui Li (2019) argues against many of Gould’s arguments he forwarded in Full House and Wonderful Life (Gould, 1989, 1996). Attempting to refute one of Gould’s arguments—that evolutionary progress is due to human arrogance—Li (2019) tries to argue that Gould objects to the idea of evolutionary progress on the basis that such “a belief in evolutionary progress may cause human arrogance and racism and even inequality among different species, and arrogance, racism, and inequality are morally wrong; thus, the idea of evolutionary progress is wrong. Such an argument is obviously untenable” (Li, 2019: 301). The thing is, Gould is not incorrect in his argument that a view of evolutionary “progress” (social Darwinisim) would lead to racism and the thought that we hold dominion over other animals. Social Darwinistic thought was indeed used to enact racist policies (Pressman, 2017), and this thought was based on a view of progress in evolution. (Rushton’s attempted revival of the scala naturae in humans can, of course, be seen in Gould’s eyes as using evolution to justify certain types of attitudes—in this kind, racist attitudes—which are due to certain kinds of thought in society.)

In attempting to refute Gould’s next argument—that value terms have no use in evolution—Li tries to show that, going off the previous argument, Gould used value judgments in trying to show that belief in evolutionary progress would lead to racist and speciesist views. In a nutshell, Li says that evolutionary progress is, quoting Ayala, “directional change toward the better.” But, as Gould has always argued, these kinds of value-judgements do not make any sense. What is “better” in one environment may mean that, in comparison to another environment, we may say that it is “worse” than another so-called adaptation. I have even said in the past that the terms “superior” (higher) and “inferior” (lower) only make sense in light of anatomy, where the head is superior to the foot and the foot is superior to the head.

Li then discusses the possibility that “natural selection” can serve as the basis for evolutionary progress, contra Gould. Gould did say that, if progress in evolution was real, any kind of progress would be wiped out during mass extinction events. Invoking Gould’s punctuated equilibrium theory, Li says that the theory states that there are mass extinctions as well as mass explosions (rapid speciation) and that those organisms that do not go extinct continue on to show forms of progress. Li then says that certain traits are not only local adaptations but non-local adaptations since they can be seen to be useful in all environments. That certain traits are useful in all environments does not mean that evolutionary progress is real; it only means that, at that time and space for that organism, the trait is useful and will persist and, if it becomes non-useful, the trait will desist in the lineage. It is only, like most everything, based on context. Li says next that although a replaying of life’s tape will lead to unpredictability as regards what kinds of animals evolve, we do know that there will be complex organisms. The emergence of a similar organism like humans would be an inevitability, says Li, which means that evolution is both directional and driven towards complexity. But, as argues Gould, McShea, and Bonner, evolution is a series of random, non-driven, processes that, through our biased lens looks like “progress.”

Li then tries to show that Gould’s drunkard’s walk argument is false. The argument goes: Imagine a drunk person leaving a bar. Now imagine a wall and a gutter. After being kicked out of the bar, the drunk has the bar’s wall behind him on one side, and the street gutter at the other. Although the drunkard has no intention of doing anything since he is extremely drunk, by statistical chance, he will eventually end up in the gutter after bouncing around the wall, near the gutter and everywhere in between. Using this argument by analogy, Gould likens the evolutionary process the same way. Li then tries to argue that Gould’s rejection of adaptationism and natural selection is the wrong way to go—but Fodor and Piattelli-Palmarini (2009; 2013) argue that “natural selection” is not and cannot be a mechanism since there are no laws of selection for trait fixation and no mind behind the process of selection. So this argument from Li, too, fails.

Lastly, Li attempts to take down what Gould terms his “modal bacter” argument in Full House. Bacteria are some of the simplest organisms on earth, while humans are some of the most complex, says Li. He also says that Gould does not deny that complexity has increased since the dawn of bacteria—another fact. Upon a close reading of Full House, it can be appreciated that the evolution of complexity is not driven; it is passive and non-driven. But Li (2019: 307-308) says that “although bacteria rule the earth, human beings are higher than them, not only because human beings have more complex organic structures but also because human beings have abilities that are higher than those of bacteria. The evolutionary history of life from bacteria to humans is a history of constant progress.” But what Li fails to realize is that Gould’s modal bacter wonderfully illustrates his case: Life began at the left wall of minimal complexity, while the bacteria are right next to this left wall of minimal complexity with random “walks” dictating the evolution of complexity. The mode of life—bacteria—as Gould (2011: 170) rightly asks, “can we possibly argue that progress provides a central defining thrust to evolution if complexity’s mode has never changed?” The bacterial mode never alters but the distribution of complexity becomes increasingly skewed toward the right away from the modal bacter during evolutionary time. But Gould (2011: 171) swiftly takes care of this claim:

A claim for general progress based on the right tail alone is absurd for two primary reasons: First, the tail is small and occupied by only a tiny percentage of species (more than 80 percent of multicellular animal species are arthropods, and we generally regard almost all members of this phylum as primitive and non progressive). Second, the occupants of the extreme right edge through time do not form an evolutionary sequence, but rather a motley series of disparate forms that have tumbled into this position, one after the other. Such a sequence through time might read: bacterium, eukaryotic cell, marine alga, jellyfish, trilobite, nautiloid, placoderm fish, dinosaur, saber-toothed cat, and Homo sapiens. Beyond the first two transitions, not a single form in this sequence can possibly be a direct ancestor of the next in line.

Li, it seems, is confused on the modal bacter argument—it is an inevitability that more complex organisms (the right wall) would arise after the less complex left wall, but this does not denote progress in the Darwinian sense; it only denotes that change and evolution is random. What this does show is, as Gould argued, our anthropocentric biases lead us to the conclusion that we are “higher” than other animals, on the basis of our accomplishments.

Using Gould’s arguments in Full House, I constructed this syllogism with the knowledge that “progress” can be justified if and only if “more advanced” organisms outnumber “less advanced” organisms:

P1 The claim that evolutionary “progress” is real and not illusory can only be justified iff organisms deemed more “advanced” outnumber “lesser” organisms.
P2 There are more “lesser” organisms (bacteria/insects) on earth than “advanced” organisms (mammals/species of mammals).
C Therefore evolutionary “progress” is illusory.

York and Clark, in their article Stephen Jay Gould’s Critique of Progress (2011) put Gould’s opposition to evolutionary and social progress well:

However, Gould also focused on contingency and the critique of progress to make a larger point about science and society. The belief in progress is a prime example of how social biases can distort science. Gould aimed to show that the natural world does not conform to human aspirations. Nature does not have human meaning embedded in it, and it does not provide direction to how humans should live. We live, instead, in a world that only has meaning of our own making. Rather than viewing this situation as disheartening, Gould saw it as liberating because it empowers us to make our own purpose. Gould stressed, similar to Karl Marx and other radical thinkers, that we make our own history and that the future is open.


Hold-outs for the claim that evolution is progressive are rare in today’s contemporary biology. Rushton was one of the last big names to try to argue that evolution is progressive. (These arguments are discussed here, here, and here.) Although Bonner used to be a progressionist, he changed his view in 2013, agreeing with Gould and McShea that evolution is random and non-driven—that it is passive. Dogo et al (2013) showed that there is no increase in muscles in the nodes leading towards Homo sapiens, so “humans are relatively simplified primates” (Diogo et al, 2013: 18). Li (2019) has some of the best attempts at taking down Gould’s anti-progress arguments but he comes up really short. Evolution just is not progressive, no matter who wants it to be (Ruse, 1996).

All in all, the concept of progress in evolution seems to be trending away from being touted as reality. As we learn more and more about the passive and non-driven evolutionary process, we will put to rest such simplistic notions of “more or less evolved”, “superior and inferior” organisms to rest. Because all organisms that are not extinct have undergone the same amount of evolutionary time and therefore have been evolving for that amount of time. This does not, of course, speak to the fact that MORE evolution could happen in certain species in certain timespans, but this DOES NOT mean that the species that undergoes more evolution is “more evolved” or “superior.” Gould, contrary to some, has definitively and convincingly put these kinds of anthropocentric arguments to bed. By conflating value judgments with evolution, we lose the beauty of what evolution really is—random, non-driven change that has caused all of the biological wonder we see around us today.