Tag Archives: Stephen Jay Gould

Evolution is progressive: Debunking Gould’s drunkard walk metaphor

14 Sunday Feb 2021

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Maybe the long-term trend across the universe is towards orthogenesis, towards greater intelligence, towards technological singularity. Just like the long-term trend for matter and energy is the formation of stars and planets, galaxies and superclusters__Ganzir, 2021

Because all living things evolved to adapt to their environments, many people deny that evolution is progressive. For example, Harvard biologist Stephen Jay Gould wrote “evolution forms a conspicuously branching bush, not a unilinear progressive sequence…earth worms and crabs are not our ancestors; they are not even ‘lower’ or less complicated than humans in any meaningful sense.”

In his book A Mirror to Nature, Science journalist Peter Knudtson writes “evolutionary theory…sees every living population of organisms on the planet as a proved evolutionary success that has by its very survival shown itself itself to be exquisitely adapted to its environment.”

He quotes anthropologist Emoke J.E. Szathmary as stating “As for superiority or inferiority–any geneticist finds this notion amusing. Each is dependent on the environmental context within which the ‘superior’ or ‘inferior’ trait (not population) evolved. Change the environment, and one may change the labelling attributed to the trait.”

Many scholars might beg to differ:

  • E.O. Wilson (1975) divided life’s history into four major stages: (1) the emergence of life itself in the form of primitive prokaryotes with no nucleus. (2) the emergence of eukaryotes with nucleus and mitochondria (3) the evolution of large multicellular organisms that have complex organs like eyes and brains (4) the emergence of the human mind.
  • In 1980 Arthur Jensen stated “the higher the animal ranks in the phyletic scale, the more seriously do lesions in the cortex of the brain affect its objectively measurable behavioral capacity”.
  • Princeton biology professor John Bonner (1980) noted that there’s been an evolution from primitive bacteria billions of years ago to complex life forms today, and the newer animals have bigger brains than older animals and that it’s perfectly natural to say that older life forms are lower than newer life forms, because their fossils are literally found in lower strata. Even plants can be ranked he argued; angiosperm > slime molds.
  • Paleontologist Dale Russel (1983, 1989) noted that the mean encephalization of mammals had tripled in the last 65 million years and that the mean encephalization of dinosaurs steadily increased for over 140 million years.  Extrapolating from the latter trend, Russel argued that had dinosaurs not gone extinct 65 million years ago, they would have eventually evolved into big-brained bipeds.
  • J. Phillipe Rushton (1989) argued that among modern humans, there was a Mongoloid > Caucasoid > Negroid hierarchy because Mongoloids split off from Caucasoids long after Caucasoids split off from Africans long after our species evolved in Africa.
  • J. Baker et al (2015) found “an overwhelming tendency for rapid morphological change to lead to larger body size in 10 of the 11 largest mammal orders, suggesting that mammals have consistently evolved toward larger size, most likely as a response to selection pressure”
  • And last but not least, pumpkin person (2017) found a positive correlations between the number of splits on the evolutionary tree a taxon was descended from, and the brain size/encephalization of said taxon.
dinosaur
Had they not gone extinct 65 million years ago, Dale Russel believes they would have evolved into big brained bipeds.

However Gould was having none of it. In his 1996 book Full House, Gould argued that life becomes more complex over time, not because complexity is superior and thus favoured by nature, but because there’s a lower limit on how non-complex life can be, so it has nowhere to go but up. In a clever analogy, Gould compared evolution to a drunkard stumbling home from a bar. Even though each step she takes is in a random direction, she can’t get any closer to the bar because there’s a brick wall, so over time she will move further and further from the bar, not because she’s trying to get away from it, but because that’s the only direction in which her random steps can slowly accumulate over time.

Analogously, evolution started as single celled organisms and thus had nowhere to go but up in complexity. So it’s not that complexity was evolutionary favoured, but rather it was all evolution had to work with.

This explanation might explain why it look nearly 3 billion years to go from singled-cell organisms to multi-cellular life, but it can not explain why it took only half a billion years to go from multi-cell life to the most complex known object in the universe: the human brain. That’s like Gould’s drunkard taking 3 hours to stumble ten feet from the bar, and then and only an extra half hour to get from the bar to Neptune.

And how does Gould’s metaphor explain why an organ as precise as the eye “has evolved independently more than 50 times in species such as flies, flatworms, molluscs and vertebrates.”. If drunk women stumbling away from bars just happened to stumble into a location as precise as your bed on 50 different occasions, would any jury believe they all just randomly stumbled there? No they’d think you drove them there, so we should think natural selection is somehow driving the evolution of an eye because it’s a superior trait to have on pretty much any planet near a star bright enough to provide light. And once you have an eye you have sensory input, and once you have sensory input, and once you have input you need intelligence because in the succinct words of a friend’s brilliant mother, intelligence is the ability to “synthesize information usefully”.

Another example of a progressive evolutionary trend is increasing body size among mammals. Now the obvious reason why mammals would get bigger over evoultionary time is all else being equal, bigger is better. Duh. But Gould would have us believe it’s because there’s a lower limit on body size, thus there’s no where to go but up. Fortunately, Baker et al explicitly tested this theory and debunked it:

We use our PAD comparisons to test for the presence of a lower bound by drawing on ideas developed in the paleontological literature (12, 21, 23, 24) while explicitly accounting for shared ancestry. If some lower boundary on size is enforced, we expect most ancestor-descendant size changes to be positive when the ancestral size is near to that limit; it is only possible to get larger. However, as the ancestral state moves away from that limit, we predict that the distribution of body size change will become increasingly centered about 0 (i.e., size decreases are equally likely as size increases) (24). Taken over all branches of the phylogeny, this pattern predicts a negative relationship between a branch’s ancestral size and the average body size change observed along that branch (12, 21). When ancestral size is small, changes will tend to be positive, but when ancestral size is large, size can change in either direction.

We do not find the predicted negative relationship (Fig. 3D and SI Text). Instead, we find that size change actually slightly increases in magnitude when ancestral size is larger (β = 0.020, P < 0.001; Fig. 3D). This pattern is also found in the paleontological data using FAD comparisons (12). To retain the idea that some physiological lower limit could produce these PAD changes and results from paleontological data (12), proponents would have to invoke a new physiological lower limit for each new species that comes into existence. Why or according to what processes these mysterious and dynamically shifting constraints arise imposes a steep hill for this explanation to climb.

Is human evolution speeding up or slowing down?

11 Saturday Jul 2020

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When I was growing up everything was nice and simple. Australopithecus evolved into Homo Habilis who evolved into Homo Erectus and about 200,000 years ago, Homo Erectus evolved into Anatomically Modern Humans who evolved into Behaviorally Modern Humans by the Upper Paleolitic. The End.

Stephen Jay Gould famously stated:

There’s been no biological change in humans in 40,000 or 50,000 years. Everything we call culture and civilization we’ve built with the same body and brain.

Or to quote Karl Marx: “Man creates himself”

Even people like J.P. Rushton who believed in racial differences in intelligence believed they were ancient differences that predated the Holocence.

I love Gould’s idea of evolutionary stagnation because it allows us to study cultural evolution holding genetics constant. Even though Gould rejected the idea of man as the evolutionary pinnacle, he nonetheless agreed that we had reached a point where we transcended the laws of nature. Cultural evolution had replaced biological evolution. We no longer had to adapt genetically because we had the intelligence to adapt behaviorally.

Unfortunately, a new crop of discoveries are challenging this beautiful notion. These scientists see culture not as a replacement for genetic evolution, but as something that accelerates it.

Brian Mattmiller writes in 2007:

…a team led by UW–Madison anthropologist John Hawks estimates that positive selection just in the past 5,000 years alone — around the period of the Stone Age — has occurred at a rate roughly 100 times higher than any other period of human evolution. Many of the new genetic adjustments are occurring around changes in the human diet brought on by the advent of agriculture, and resistance to epidemic diseases that became major killers after the growth of human civilizations…

…The findings may lead to a very broad rethinking of human evolution, Hawks says, especially in the view that modern culture has essentially relaxed the need for physical genetic changes in humans to improve survival. Adds Hawks: “We are more different genetically from people living 5,000 years ago than they were different from Neanderthals.”

Gould must be spinning in his grave over that last quote.

Hover Steven Hsu writes:

Roughly speaking, modern humans differ from chimpanzees with probability 0.01 at a particular base in the genome, from neanderthals with probability 0.003, and from each other with probability 0.001 (this final number varies by about 15% depending on ancestral population).

So if random members of different different races only differ by 0.00085 to 0.00115, and if random humans differ from random Neanderthals by 0.003, how is it even mathematically possible for people 5000 years ago to be closer to Neanderthals when modern races split long before 5000 years ago? Indeed the split between Africans and non-Africans occured about 70,000 years ago and splits within Africa may be as old as 250,000 years.

But perhaps Steve Hsu is talking about the total genome while Hawks is only talking about the part of the genome that experienced adaptive selection. But it begs the question, if people 5000 years ago were more similar to Neanderthals in such important ways, then were they even people? By definition, shouldn’t members of our species be more similar to us than they are to members of another species?

Further confusing the issue, recent headlines claim human evolution is slowing down, at least if mutation rate is any proxy:


Over the past million years or so, the human mutation rate has been slowing down so that significantly fewer new mutations now occur in humans per year than in our closest primate relatives. This is the conclusion of researchers from Aarhus University, Denmark, and Copenhagen Zoo in a new study in which they have found new mutations in chimpanzees, gorillas and orangutans, and compared these with corresponding studies in humans.

[Correction July 11, 2020: a previous version of this article incorrectly dated Stephen Jay Gould’s quote. Thank you commenter RR for pointing out the error]

Is evolution progressive?

20 Thursday Jun 2019

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Paleontologist Dale Russell believed that had dinosaurs not gone extinct, they would have evolved into big brained bipeds very similar to us

In a trivial sense, almost everyone agrees that evolution is progressive in some ways. The average life form on Earth today is far bigger, more complex, more intelligent and more beautiful than the average life form 3.5 billion years ago, when life began.

However this does not prove that evolution favors more complex organisms because they’re superior, which is what is truly meant by evolutionary progress. It could just be that it takes time for complex life to evolve, and since life started with minimal complexity, it had nowhere to go but up.

Stephen Jay Gould uses the analogy of a drunkard’s walk. Gould’s anology is explained by Robert Wright:

A drunk is heading down a sidewalk that runs east-west. Skirting the sidewalk’s south side is a brick wall, and on the north side is a curb and a street. Will the drunk eventually veer off the curb, into the street? Probably. Does this mean he has a “northerly directional tendency”? No. He’s just as likely to veer south as north. But when he veers south the wall bounces him back to the north. He is taking “a random walk” that just seems to have a directional tendency.

If you get enough drunks and give them enough time, one of them may eventually get all the way to the other side of the street. That’s us: the lucky species that, through millions of years of random motion, happened to get to the far north, the land of great complexity. But we didn’t get there because north is an inherently valuable place to be. If it weren’t for the brick wall—that is, the fact that no species can have less than zero complexity—there would be just as many drunks south of the sidewalk as north of it, and the randomness of all their paths would be obvious. Gould writes, “The vaunted progress of life is really random motion away from simple beginnings, not directed impetus toward inherently advantageous complexity.”

The problem with this metaphor is how far North does the drunk need to get before the wall no longer explains his progression? If you found 100 drunks that were all 100 miles North of the wall and came back a month later and found those same drunks were now on average 200 miles North, then obviously something other than the wall is moving them North because once you get 100 miles North, the odds of randomly stumbling 100 miles South are like the odds of flipping a coin and getting 100 consecutive heads.

So Gould’s argument can plausibly explain why single cellular organisms evolved into multi-cellular organisms, but it can’t seem to explain why organisms that are already 100 miles North of the wall also show increasing complexity.

Paleontologist Dale Russell (1989) found that the encephalization quotient (ratio of brain weight to expected brain weight for body size) of mammals more than tripped in 65 million years of evolution. It seems extremely unlikely that this tripling can be explained by Gould’s “no where to go but North” metaphor because brain size can certainly decrease in size, and even vanish all together.

On the other hand, there might be a survivor bias in Russell’s dataset in that the descendants of those mammals that decreased their brain size are no longer considered mammals, leaving only bigger brained mammals in the sample.

What is needed is a study that compares the brain size of extinct animals with the brain size of their living descendants. If most of the latter are bigger brained than most of the former, then Gould’s metaphor is debunked, and evolution really is progressive.