Why does the human Y chromosome share more sequences with gorillas than chimpanzees?

This post does not have much to do with memes, but it does relate to early human evolution.

In particular it discusses reticular great ape evolution. The main evidential basis for the post is the observation that gorilla Y chromosomes are more similar to human Y chromosomes than they are to chimpanzee Y chromosomes. This is a widely recognized fact. It is true despite the family tree weakly predicting the opposite finding:

The Y chromosomes of great apes represent a particular puzzle: their gene content is more similar between human and gorilla than between human and chimpanzee, even though human and chimpanzee share a more recent common ancestor.

An obvious and conventional explanation for that is that the chimp lineage experienced rapid Y chromosome evolution, leaving humans and gorillas with relatively similar Y chromosomes. This could have something to do with sperm competition and the huge chimpanzee testicles. That's the conclusion drawn here:

we found that the genus Pan, which includes chimpanzee and bonobo, experienced accelerated substitution rates. Pan also exhibited elevated gene death rates. These observations are consistent with high levels of sperm competition in Pan.

Mystery solved - right? Maybe. Here, I would like to draw attention to another pair of possibilities:

Maybe a male gorilla mated with a female human ancestor - and now all human males are now descended from him. Or maybe the opposite scenario is involved: maybe a male human ancestor mated with a female gorilla and now all male gorillas are descended from him.

I think that we have to downgrade the probability of these explanations since they involve unlikely reticular evolution and hybridization. However, while hybrids are rare I think that geological time up-regulates their potential evolutionary significance. Basically, Eugene McCarthy has convinced me that we should consider hybridization much more seriously.

Can we test these theories? Yes, I think they can be tested using geonomic comparison data. In addition to a similar Y chromosome, we should expect subtle changes in the rest of the genome. Back-crossing would dilute, but perhaps not completely eliminate traces of the hybridization event.

Assuming a male chimpanzee donor, some small areas of the human genome would be less similar to chimpanzees and more similar to gorillas. That's expected anyway, but with hybridization, there would be more donor DNA involved. We could compare in both directions (human -> gorilla and gorilla -> human). If there's a big difference, hybridization becomes more likely. We could possibly even use molecular clocks to determine when shared sequences diverged between the lineages.

Which of the two scenarios I mentioned is more likely? I think that is unclear, but the scenario involving the male gorilla seems as though it would be the more dramatic finding for students of human evolution. Relationships between male gorillas and female humans have been dramatized in King Kong and its sequels. It would be a curious finding if those movies mimicked real evolutionary history.

Part Primate, Part Pig

In 1976, Richard Dawkins wrote: "Most of what is unusual about man can be summed up in one word: 'culture'."

Genetic differences between humans and chimpanzees would thus likely be explained by a theory of gene-meme coevolution. Or so I have assumed for a decade or so.

Now a rogue scientist has come up with a very different explanation for the differences between humans and chimpanzees. He substitutes "culture" with "pigs".

"Most of what is unusual about man can be summed up in one word: 'pig'. The hypothesis is that a pig and a great ape mated and produced viable offspring. Some of their genes persisted in the population and eventually came to dominate it. Their descendants are modern humans.

This is not a very new idea. Eugene McCarthy as been promoting it for over a decade. For a while. phenotypic similarities were the main evidence. However, now Eugene has performed a genetic analysis that he claims provides solid evidence for the theory. The paper is: "Human Autosomal Nucleotide Positions Differing from Bonobo Instead Match Pig".

It is an amazing, surprising result. If replicated it will likely turn much of our understanding of human evolution on its head. Eugene's data shows that the Y chromosome has a lot of pig influence, while the X chromosome doesn't have any. This implies that the pig males mated with monkey females - and not the other way around. The Y chromosome doesn't cross over, so it means humans basically have a pig's Y chromosome. How come nobody noticed this before? I don't know, but it does look as though the Y chromosome is similar to that of a pig. Various papers have pointed out its oddities.

The pig Y chromosome estimated to be 50Mb here. That is similar to human at 57 Mb. Different from chimpanzee at 25Mb. The conventional explanation is: more sperm competition in chimps generates selection pressure favoring small size. Another site says: ""Puzzlingly, in terms of shared genes and overall architecture, the human Y is more similar to the gorilla Y than to the chimpanzee Y even though human and chimpanzee have a more recent common ancestor."

The evidence from the sex chromosomes is interesting and it could be easy to verify. However the rest of the genome is where the main evidence lies.

Eugene's study needs to be reviewed and replicated - but it is looking as though this could be an important find for those interested in human evolution.

Update: Eugene checked - and the human Y chromosome is more similar to chimpanzee than it is to pig - according to his metrics. It is consistent with the hypothesis of the hybrid inbvolving a male pig - since the pig Y chromosome could still subsequently go extinct in the population.

For more on the gorilla-related evidence see here.

Memetic strategies

Here are a few lists of meme-related strategies. The first list was inspired bt an Alex Mesoudi paper that laid out a fairly conventional view aligned with the work of Boyd and Richerson. Sorry, no link today.

What strategies do people (adopters) use to acquire good memes from others (sources)?

• Are the memes popular?
• Are the memes repeated?
• Do the memes attract attention?
• Do the sources have high-prestige?
• Are the sources related to the adopters genetically - do they share genes with them?
• Are the sources related to the adopters in other ways - do they share memes or environment with them?
• Are the memes likely to benefit the genes of the adopters?
• Are the memes likely to benefit the existing memes of the adopters?

As well as sources resembling them, the adopters can sometimes be interested in whether the sources resemble the adopters in *relevant* ways.

Some of these strategies can be faked or corrupted. For example, high-prestige people could be being paid to appear to associate with the meme, in order to manipulate others into adopting it. This is a common advertising trick. What strategies do memes use to get acquired by others?

• Be memorable
• Be copyable
• Acquire and gain control over resources
• Promise to benefit the host - and deliver on the promise.

To persist in their new host, candidate memes typically have to pass additional hurdles once acquired:

Are the memes compatible with existing attitudes and beliefs?

Are the memes sufficiently memorable?

Prevent rival memes from being adopted

Destroy rival memes already present in the host

Do the memes cause conflict or trouble?

Are the memes useful or helpful?

If memes do not appear to be helpful, might they be so in the future?

Robin Hanson - Beware cultural drift

Robin Hanson has become interested in cultural evolution in 2024. He read Not By Genes Alone, The Secret of our Success, Cognitive Gadgets: The Cultural Evolution of Thinking - and a number of other books on the topic. He has also made some blog posts and videos in the area. Here's a recent video on the topic:

My picture seems significantly different from Robin's. I see meme reproduction at the expense of gene reproduction - likely followed by a machine takeover. I do not forsee innovation grinding to a halt - instead intelligent machines will promote innovation. Robots will become the main consumers. The economy is unlikely to go into decline. The Amish are irrelevant - their rise is too slow to make a difference. We didn't break civilization and civilization is unlikely to collapse. I suspect that the basic problem is that Robin's timelines for the development of machine intelligence are too long.

Rob Boyd & Pete Richerson - Cultural Evolution, Human Brain Increases, AGI, & Fertility Declines

A new Boyd & Richerson interview:

Are AIs really our descendants?

While I'm criticising the positions of Robin Hanson, I reviewed his 2023 article titled: "AIs Will Be Our Mind Children" - which contains the following:

But — and here is my main point, so please listen carefully — future human-level AIs are not co-existing competing aliens; they are instead literally our descendants. So if your evolved instincts tell you to fight your descendants due to their strangeness, that is a huge evolutionary mistake. Natural selection just does not approve of your favoring your generation over future generations. Natural selection in general favors instincts that tell you to favor your descendants, even those who differ greatly from you.

I think this paragraph shows a basic failure to distingush between memes and genes. Robin says as much - by defining "genes" as follows:

Your “genes” are whatever parts of you code for your and your descendants’ behaviours.

That definition classifies memes as genes. AIs are our "Mind Children". They are likely inherit from our memes, but not from our DNA genes - at least not unless we expend considerable effort to preserve information in our genes.

You can't just throw around terms like "descendants" and "generations" in the way that Robin does. Descendants on which lineage? Generations of which lineage? Are we talking about memes or genes here? It really does matter. What Robin is doing is "muddling together" all forms of inheritance.

To call such machines our "descendants" ignores the fact that modern organisms - like humans - are menageries. They contain many indpendent inheritance pathways. Each has its own notion of what consitututes a "generation". Machines will inherit from our memes, but our genes are unlikely to be impressed by that. Rather they will complain about their germ line being wiped out. We do indeed see protests of exactly that kind. This is not a "huge evolutionary mistake" as Robin claims - instead it is one lineage complaining about competition with another lineage.

Natural selection does not favor instincts that tell you to favor your descendants indiscriminantly. According to Robin's classification scheme, excreted gut bacteria are classified as "descendants". It seems as though my DNA genes are likely to get prioity treatment if there is much of a conflict of interest.

Overall, I was not very impressed with Robin's argument here.

References

• Problems with Robin Hanson's Quillette Article On AI

The demographic transition revisited

I have an existing article about "Memes and the demographic transition". It has a number of pointers and references, but I reviewed it recently and one thing it doesn't really have is a brief summary of the theory. So, here goes:

Memes are the cause of the modern fertility fall now seen in most western nations. The phenomenon is widely known as "the demographic transition". How does that work? Like this:

• Organisms are typically resource-limited;
• Memes compete for reproductive resources with DNA genes;
• Memes are getting the upper hand in this battle due to a number of factors including progress;
• Meme interests are now less aligned with host interests due to meme horizontal transmission.

That's it. Between them these four points explain the vast majority of the dynamics of the demographic transition.

To unpack the points:

• Resource limitation - means that resources available for one application are not available for other appications. In other words using resources is subject to an opportunity cost. Resource limitation is ubiquitous.
• Memes and genes compete for resources - resources spent producing babies and DNA genes are resources not spent on learning and propagaing memes - and visa versa.
• Memes are winning - or at least their power and influence are rising.
• More memes are parasitic - This is due to horizontal transmission of memes with respect to the host generations. Once, humans lived in small groups and got many of their memes from family members. This is no longer the case and most memes are obtained via "horizontal" transmission. This path is more likely to be occupied by parasites. Some will behave like the Ebola virus: liquidate their host as fast as possible. Others will merely sterilize their hosts and redirect their resources into meme propagation.

For more details and some references, see the "Memes and the demographic transition article.

This article is partly in response to Robin Hanson's article titled: Beware Cultural Drift.

Robin claims: "The clearest proof of biologically maladaptive culture drift is fertility". That does not seem right to me. "Drift" has a specific meaning in biology - it refers to the absence of selection. Here the memes are not "drifting" away from some adaptive peak. They are actively and deliberately sabotaging the fertility of their human hosts and using the resulting resources for their own ends. Drift is a sideshow.

Rob Boyd - A Different Kind of Animal: How Culture Transformed Our Species

I read through some of the the reviews of Rob Boyd's 2017 book "A Different Kind of Animal: How Culture Transformed Our Species". To my surpise I saw that Boyd was ravaged by a meme enthusiast:

Although Boyd clearly focuses on norms, unfortunately he does not dare to 'leap' and come to the – in my view – logical conclusion: That the focal entities in cultural evolution are not individuals or even groups of individuals, but non-genetically transmitted pieces of information: ideas, norms, practices … or what others have called 'memes'.

Boyd writes: „...competition among groups can lead to the spread of some norms at the expense of others“. „Norms causing a group to survive will become more common compared to those that lead to extinction“.

That is very close to what Dan Dennett or Richard Dawkins would call a 'meme's-centered view' of cultural evolution. In biological evolution, the last sentence would be like this: „Genes causing an organism to survive and reproduce (compared to other organisms) will become more common compared to those that lead to a reduction of fitness or even death“. Therefore, imo the logical conclusion of „cultural group selection“ would be a 'meme's-centered view' of cultural evolution, but since Boyd does not like the concept of 'memes' he continues to speak of 'norms', sometimes in a rather ambiguous way.

The reviewer goes on to say:

That is one of the weaker points of Boyd's book: His poster examples from anthropological studies make perfect sense in a functionalist framework, as they are all about norms that have a strong (positive) effect on survival of HUMAN beings (useful food taboos, detoxifying material to obtain food, building shelters, etc..), but many, maybe even most of cultural variants (aka 'memes') do not have such effects. A lot of those entities culture is made of exist - and are reproduced - just because people find them interesting and memorable. That is exactly what is predicted by scholars who consider cultural variants aka 'memes' as a second replicator with its own independent 'fitness'.

I didn't read " A Different Kind of Animal" yet - but to be fair, this might be being a bit unfair to Rob. He's authored (or coauthored) many papers that use the "meme" terminology. He does understand that memes can be deleterious to their human hosts. There's a while chapter on this topic in "Not By Genes Alone". However constant use of "norm" as a substitute for "meme" does seem to be a kind of cancer in the field. Cultural evolution involves the study of memes, not just norms. Not all memes are norms.

Meme adjectives

A recent "Know Your Meme" editorial reminded me that I had never seen a list of meme categories or meme adjectives. I thought I would make a list of meme adjectives (loosely defined) - ordered by popularity:

• new memes (118,000,000 results)
• best memes (111,000,000 results)
• internet memes (46,400,000 results)
• funny memes (44,300,000 results)
• old memes (41,200,000 results)
• cat memes (40,500,000 results)
• girl memes (37,800,000 results)
• dog memes (32,100,000 results)
• great memes (23,200,000 results)
• boy memes (19,600,000 results)
• dank memes (13,400,000 results)
• viral memes (11,500,000 results)
• funniest memes (8,000,000 results)
• wholesome memes (7,720,000 results)
• fail memes (6,810,000 results)
• horror memes (6,870,000 results)
• fine memes (5,630,000 results)
• romantic memes (5,090,000 results)
• worst memes (3,540,000 results)
• greatest memes (3,140,000 results)
• asmr memes (2,080,000 results)
• creepy memes (1,940,000 results)
• moldy memes (1,590,000 results)
• deep-fried memes (343,000 results)

This is probably not an exhaustive Am I missing anything big? Can you improve on my methodology? Let me know in the comments. Thanks.

Dan Dennett: From Genes To Memes:The Evolution of Language and AI

One notable part is around 25 minutes in. Dennett complains about intelligent machines creating counterfeit people - and then proposes making counterfeit people illegal. No more Batman. No more Spiderman. No more Superman. It seems like an absurd proposal to me. What can Dennett be thinking about?

Memes start around 45 minutes in.