Stephen Jay Gould's blind spot

It is 20 years ago that Stephen Jay Gould died, and 50 years since Niles Eldredge and he proposed the theory of punctuated equilibria. Here I discuss how their ambition to build a macroevolutionary theory led to a striking conceptual blind spot that continues to cause negative ripples in the pond of evolutionary biology.

[pedromartinez-serra]

This is another great video. Brought me old memories, when in the 90’s I was eagerly expecting the new issue of Natural History, mostly to read Steve Gould’s pieces. Memorable writing!
By the way, I would like to hear a bit more on your opinion of punctuated equilibrium (not necessarily two hours!). I got the impression that the theory was more about timing of phyletic change in different lineages. Is that still standing? Is punctuated equilibrium representing the rate of morphological change in different clades?
OK, time to get a glass of wine….
😀

[IvoTichelaar]

Funny thing, I met you in Scheltema bookstore circa 1999 after you supervised some course work of mine, and you told me which books you were looking at. You mentioned Gould and I bought a Gould book. I think it was The Panda's Thumb. I enjoyed it and it introduced me to a more holistic way of thinking about biology. I later picked up Wonderful Life about the Burgess shale and enjoyed that a lot too.

I tend to be mild on Gould. He seemed to get into a line of reasoning and then defend it at all cost. He didn't seem aware. In that sense, he was a very normal person. :-)

In some ways, his reasonings in his popular science writing are quite romantic and I think this goes to the heart of his conflict with Dawkins. Dawkins reduced evolution to changes in and selection on alles of individual genes. Gould insisted that natural selection works on organisms, the combination of all its alleles of all its genes. They are of course both right.

I was taught punctuated equilibrium as fact during my master's. I think the idea had merit, since environments tend to buffer themselves and keep environmental conditions stable. No selection pressure for a well adapted species.

[IGLUPhylogeny]

Hello, the concept of the lineage thinking and the cladistic blindfold surely deserves more attention from public educators and teachers.

I've always been baffled by arguments such as "humans haven't evolved from apes, we just share a common ancestor with them". But the chimp-human last common ancestor was rather accurately reconstructed and it was clearly an ape (hairy, quadrupedal and so on), of course it was not a chimp but overall it was more similar to chimps and gorillas than to modern humans.

Similarly I was baffled by the rejection of linear evolutionary imagery. I have always thought that phylogenetic trees can be visualized as a long line of parents, grandparents, great-grandparents and so on, stretching back to the origin of life (or in the most simplified version (in case when I'm interested only in my ancestors and not in the ancestors of eg. barnacle) just a single long line beginning with me, my mother standing next to me, grandmother standing next to my mother, and the rest of mothers forming a line all the way to the origin of life ca. 4.4 billion years ago). Such linear evolutionary imagery of course doesn't imply that a lobe-finned fish was destined to become a rabbit or a triceratops or a human in the distant future, it's just looking back at the history - it's just like genealogy: my ancestors 1000 years ago had no intention to "create" me, although their actions were totally neccessary for me to exist.

Fortunately I have read Dawkins' book "The Ancestor's Tale" and several other books on evolution long ago. From one of those books, I remember a cladogram (composed of taxa A, B and C, taxa A and B are sister taxa) explaining how a taxon A (for example sheep) is cladogenetically closer to a taxon B (for example whale) and at the same time the taxon A (sheep) is ANAGENETICALLY (but not cladogenetically) closer to a taxon C (for example llama) - this I think is an another often ignored aspect of evolution and explains the preconception of the following style: for example "morphologically, chimps are the most closely related to humans so they must be the most similar of all animals to humans", when in fact humans could be more similar to gorillas (this is just an illustrative example which may not be completely true in the case of humans and chimps, but there are many such similar cases where paraphyly is involved, i.e. the sister monophyletic taxon doesn't have to be automatically the most similar one - this must be decided by the ancestral state reconstruction and cannot be just seen from a naked cladogram). In other words, each lineage of a cladogram can be assigned a number of changes between each nodes and terminal taxa and to decide which species are more similar means to sum up these numbers of changes and not just count the number of nodes between terminal taxa. Maybe some people think of the phylogenetic trees as diagrams depicting how similar species are instead of the real depiction of genealogy?

Another common misconception is the case when for example ctenophores were found to branch off as the first lineage from the rest of animals, then many people wrote that the ctenophores were the first animals, without realizing that the stem lineage of Ctenophora was inhabited by ancestors which were not ctenophores and ctenophores could be much younger than some cladogenetically more distant taxa, eg. chordates. But of course evolution is gaining/losing one character after another and not gaining all characters defining a taxon at the same time, for example I have read an article claiming Yanjiahella can't be an echinoderm because it lacked the stereom despite the fact it was considered to be a STEM echinoderm and thus to be expected not to have some features of the crown group echinoderms.

It's a shame that we don't see more phylogenetic trees with images of reconstructed last common ancestors at the individual nodes. Many common ancestors were accurately reconstructed, especially when paraphyletic taxa were identified - for example last common ancestor of rabbit and carrot was an excavate flagellate which lived cca 2 billions years ago. This excavate flagellate was reconstructed in great detail (types of flagella, groove, size etc.), unlike the last common ancestor of rabbit and scorpion, a marine worm living more than 540 mya about which we know almost nothing (flattened or cylindrical?, sessile or motile?, segmented?, through gut?, microscopic or 20 centimeters long?, ventral mouth?

Unfortunately most of depictions of evolution, like for example "OneZoom-Tree of Life Explorer", are just mere naked cladograms - at least they should have put reconstructed last common ancestors at those nodes where possible.

Recently it looks like we are approaching the true phylogenetic tree (for example Xenacoelomorpha sister to monophyletic Nephrozoa, Ctenophora sister, eukaryotic root among Excavata, Archaea paraphyletic). Then fossils will be "grafted" on this stable tree to elucidate morphology of those lineages for which there are no living examples, for example vetulicolians and yunnanozoans could be paraphyletic assemblage of stem chordates, Ediacaran dickinsoniomorphs ("Proarticulata") could be stem planulozoans (clade comprising Cnidaria, Bilateria and Placozoa).
Ancestral state reconstruction then can reveal that a certain fossils are indistiguishable from the last common ancestor so that Tiktaalik-like fishapod can be depicted not as a sister branch but as a direct ancestor (for example the reconstructed last common ancestor of the fishapod Tiktaalik and rabbit was so similar to the fossil Tiktaalik that a Tiktaalik fossil and the fossil of the real last common ancestor were indistiguishable because fossils are always more or less incomplete).
Fortunately in some case we don't even need any fossils to reconstruct the common ancestors - an example: the last common ancestor of living eukaryotes, because the living excavates are highly paraphyletic AND they are all morphologically very similar AND they are not similar because of the convergent evolution.

And this I think is the main goal of this whole research endeavor: to have an accurate "linear evolutionary imagery" and not just the naked cladogram with mere bifurcating black lines connecting the taxonomic names at the tips of the branches. Those black lines are where the real interesting evolution happened.
In other words, one of the main goals of reconstructing cladogenesis is to reconstruct anagenetic changes which happened along the individual lineages.
This accurate "linear evolutionary imagery" will depict the maximal amount of ancestors between any living/extinct species and the LUCA (or FUCA), documenting as many evolutionary changes between the generations as possible, without any large gaps.

[mapleveritas]

I am definitely not an evolutionary biologist. And I read Gould for fun. Obviously I will get some (or all) of the concepts wrong. I don't know whether what you say about Gould is correct or not. I don't have the background to be able to tell for sure. I am confused about what you about his idea, that evolutionary lineages are bushy. I am a birder, once in a while, I would find a woodduck with a mallard mate. I also see ducks that are obviously hybrids. Now, I don't know whether these hybrids are fertile or not. If for whatever reason, like the descendants of neanderthals and human beings, the hybrid is indeed fertile, how do we draw the lineages? That is not even a bush, as each branch of a bush has exactly one "ancestor". In this case, these human beings have two ancestral species. Unless neanderthals are not considered a separate species. Then how do we define what a species is?

Of course, I can be completely confused about each and every point I raised here. If so, I would like to be enlightened.

[gunterwagner]

Well I do not agree with Gould but what makes his stance logically possible is that his theory of punctuated equilibria says that change ONLY happens during speciation and not during the existence of the species lineage between speciation events. I think that makes his point coherent, event though factually false. Günter Wagner