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I remember reading (a long time ago so can't provide a reference) that in 1000s of years most humans would have an extra finger. I'd assumed that this was because of the evolutionary advantage it would have given their forebears, although I would question how much natural selection applies to rational beings like humans these days. But on a quick bit of reading now, it seems like it could be because it is a dominant trait. Although after a bit more reading, it seems it might not become more common over time due to the Hardy-Weinberg principle[0].

[0] https://en.wikipedia.org/wiki/Hardy%E2%80%93Weinberg_princip...

3 comments

I know it was just an aside, but I can't let this go:

>I would question how much natural selection applies to rational beings like humans these days.

It's a universal principle, why wouldn't it apply? Each generation is composed of the offspring of those members of the previous generation who reproduced, introducing a statistical bias. Why would it be different "these days", and what has rationality got to do with it?

Besides - as for the notion of 'rational' humans, especially in the context of sex and reproduction - I'll get my coat.

> It's a universal principle, why wouldn't it apply?

Because ever since we've invented writing (and arguably even before that - ever since we've invented spoken language), we've left the domain of biological evolution. We now accumulate, evaluate and discard knowledge and technology couple orders of magnitude faster than natural processes. From nature's POV, the entire ~10k years of human civilization happened in a blink of an eye (and note that all the interesting things happened arguably in the last couple hundred years).

There is still differential production of offspring who produce offspring. The selection is against kind of people who have few children or have few children who go on to have children themselves. That’s how it always has been and always will be unless we abolish natural reproduction.

Again, whatever effect this selection has (with quantized increments of the length of a generation), it's completely drowned in memetic and technological evolution(s) which currently operate at the speed of Tweet. In your particular example, this arguably derails biological evolution completely - the decision to have kids, and how many kids to have, is dominated by economic and (secondarily) cultural considerations, which change significantly between generations. Evolution will have hard time identifying genes to promote, when the minimum unit of change is probably "how smart people are" or "how social people are", both having many more reasons for being favoured by natural selection.

It’s a messy process, and we may not be able to see where it’s going, but you can bet that there will be changes in human phenotypes and their prominence over the course of many generations.

>Evolution will have hard time identifying genes to promote, when the minimum unit of change is probably "how smart people are" or "how social people are", both having many more reasons for being favoured by natural selection.

If I understand you correctly, that’s just not true. In his seminal work, The Selfish Gene, Richard Dawkins showed that the individual gene is the unit of selection. A genotype that tends to result in a slightly stronger preference for a family life is exactly the kind of thing that could become more prominent, even within one or two generations. I’m sure this is happening right now.

>In your particular example, this arguably derails biological evolution completely - the decision to have kids, and how many kids to have, is dominated by economic and (secondarily) cultural considerations, which change significantly between generations.

I was not making a particular example at all. That is the function of natural selection: it selects for the genotypes had by those who have children who go on to have children themselves.

The selection doesn’t have to happen at the level of a preference for kids. A gene related to diligence or conscientiousness or just about anything else can have effects that ultimately cause differential reproductive success for you and your offspring.

The fact that it’s all too complicated for us to model has bearing on it at all.

10,000 years isn't that short a time in a rapidly changing environment, though it would be in a static one. Human mematic evolution fed into human genetic evolution in a number of ways over that timeframe. As people started getting most of their calories from farming they didn't have as much dietary vitamin D and their skin got lighter. People in Eurasia got more resistant to contagious disease and were able to live together in larger groups, accelerating memetic evolution.

Gould came up with the excellent name "punctuated equilibrium" for the discontinuous nature of genetic change, though the math describing it had existed before he popularized the concept.

It is true, though, that all the big changes of the last 10,000 years seem to have been simple changes in individual genes or their expression rather than more complex changes.

So you're saying that a 6-finger person has a larger change of having children than the person with 5 fingers?

Here's a reality check: 6-finger people also have a much higher probability to be bullied at school and thus never reproduce than the others.

No, that’s not what I’m saying. I’m responding to the assertion that there is no evolution of humans happening at all.

On the timescales evolution operates over, humans being technological creatures in a civilization is essentially a blip. Not relevant whatsoever.

In a few more thousand years, we'll either have transcended biology altogether, be extinct, or be back to the kind of pre-civilization environment where the slow work of evolution matters again.

I think the brain is currently under tremendous evolutionary pressure and is being pushed in a number of directions at once.

Anatomically modern humans have been around for 100-300 thousand years (definitions vary and evidence is scarce and ambiguous). Our bipedal (i.e. hands free to do dexterous things) ancestors go back ~4 million more. If acquiring extra fingers was a net advantage we'd all have them already.

"If acquiring [new trait] was a net advantage, we'd have it already."

If this principle were true in general, it would imply that evolution didn't exist.

Environments change. Competitive landscapes change. Diets change. Parasites/diseases change.

There are genes in humans that are currently undergoing strong selection.

https://www.nature.com/news/massive-genetic-study-shows-how-...

> If this principle were true in general, it would imply that evolution didn't exist.

But it's not true in general, and I gave a specific context: millions of years of human ancestors using their hands to survive in a wide variety of environments and occasionally being born with extra fingers (~0.2% in modern humans, so probably a huge number of opportunities). We have five fingers, so it is unlikely that our six-fingered ancestors had a significant net advantage in general.

I remember reading an article about a present day man with 12 fingers and 12 toes who believes he has an advantage climbing coconut palms. If needs like that had been providing consistent evolutionary pressure on our ancestors, things might be different. Edit: here's a version of it: https://www.cbsnews.com/news/man-with-12-fingers-12-toes-cal...