Tag Archives: Stephen Jay Gould

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.