I’m sure you’ve heard the assertion that everyone who has blue eyes is descended from the same person.
Wouldn’t that mean that the mutation occurred only once in all of human history? How likely is that? Every blue-eyed native African shared an ancestor with every native Sámi?
What about heterochromians?
Not necessarily. The mutation could have occured multiple times, but in all but one case, the individual did not have children (or had children who did not have children…)
Given thousands of years for the gene to spread, that is certainly plausible.
Both of those hypotheses seem very unlikely to me. And they seem to contradict each other in principle
You have to define “blue eyes”. For example, apparently a number of members of the Ari people in Ethiopia have blue eyes, but this is linked to Waardenburg syndrome.
Doesn’t every human share an ancestor with every other human?
I assume he meant that every blue eyed native African shares a blue eyed ancestor with every blue eyed Sami.
Which doesn’t appear correct, or at least, depends on your definition of “blue eyed”.
That is exactly what is claimed.
This one goes into a bit more detail, and it’s not quite all, but very nearly:
Notably, the study didn’t include any blue-eyed Africans, but I’m guessing stuff like Waardenburg syndrome falls into that 3%.
Gotcha, that makes a lot more sense then
I assumed that claims of “all” were considering stuff like Waardenburg syndrome to not be “true” blue eyes. That the claim would be made that they look blue, but the underlying cause is different, therefore they aren’t “the same thing” as “true” blue eyes.
Which, sure, you could define “blue eyes” to mean something like that, but then “all people with blue eyes due to this specific underlying mechanism caused by this specific mutation” is nearly tautological.
Isn’t that how all evolution works? A mutation happens once, and then spreads.
Some sites are prone to mutation so that mutations can occur in multiple individuals.
Some traits can occur due to multiple different mutations (lactose tolerance occurred multiple times, in different ways).
Also, some important mutations take only the mutation of a single gene, and so are much more likely to spontaneously happen over and over. The mutation that causes sickle cell anemia for example; it happens all over the world, but as it grants malaria resistance it gets selected for in malarial regions despite its downsides (malaria is nasty).
By analogy, as far as I know, every person in the world with the last name “Asimov” is descended from Judah Asimov - because he is the one who adopted that spelling of the last name otherwise transliterated as Azimov (or Azimoff) - a simple mutation. If his descendants spread around the world, every one of them will be able to trace their last name back to Judah
Every person in North America who was born Tremblay at birth (ie not counting people who married someone named Tremblay) are descended from one couple in New France, Pierre Tremblay and Ozanne Achon.
Not always - sometimes similar traits evolve over and over.
This book really expanded my understanding of how evolution works. It describes a couple of experiments in evolutionary biology, the most notable of which involved anoles in the Caribbean.
Long story short: a bunch of Caribbean islands have anole lizards. Anoles come in a wide variety of shapes, colors, and sizes, but on these islands they fell into five or so groups. Some were big and short legged and brown and lived on the trunks of trees; others were small and green and had long legs and lived in the canopies.
For a long time, it was assumed that they evolved as you suggest. A mutation happened and the lizards became short legged and brown, well adapted to trunks, and then they spread to the other islands on vegetation rafts or whatever; meanwhile, another anole became green and a high climber, and then spread to all the islands; etc.
But when they did genetic studies, they found something fascinating: the different lizard species on each island were more closely related to other lizard species on the same island than to lizards who looked like them on other islands. It turned out that each island was colonized by an ancestral population of anoles, who then evolved along one of five or so paths with remarkable regularity.
The experiment described in the book took anoles to tiny islands, ones so small that when a big enough hurricane came through they were completely submerged and thus wiped clear of animal life (and so had no anoles). They put a few anoles on each island, and came back after a handful of years (they kept having hurricanes reset their progress so they couldn’t get an interrupted stretch longer than something like a decade) but even in that limited time they were able to show that the anoles they’d catch and measure were noticeably browned and shorter legged if they were living on a trunk, greener and longer legged if they were living high up, etc - in other words, they observed the very beginning of the process of speciation. And it happened in years, not decades.
The book shares a number of other examples - guppies who colonize rock pools higher up on their home island after big rainfalls (because there’s enough water coming down the side of the hill that they can swim upstream) and finding pools with no pike cichlids become far more colorful in a handful of generations, for example.
Now, what’s interesting is, the book points out that it doesn’t always work that way. It shares another study, one where the opposite happened, closer to our traditional understanding - a mutation happened only once and the only examples of the trait are in daughter populations from that mutation.
In this study, they took 12 jars of E coli and grew the bacteria inside, studying how they and how quickly they reproduced. The strains followed similar paths, and when they tested what mutations had occurred and how they impacted the chemistry going on in the jars, they found that the same things were happening across the populations, although at different rates and in different order.
And then, after this study had gone on for a long time, many thousands of generations, something completely new happened: one population gained the ability to grow on a new substrate (Citrate) which E coli usually cannot do (in the presence of oxygen, which the jars had).
This had happened roughly 30,000 generations in. They went back to frozen samples from prior generations and found that they could “replay” the evolution of this trait, but only if they started with a sample after the 20,000th generation - if they started any earlier, the Cit+ trait never evolved. And almost 20 years later, the same trait never appeared independently again.
So it seems as if evolution works quickly and predictably most of the time, but every once in a while something that’s truly rare happens and changes the course of evolution in entirely novel ways.
I really recommend the book - it blew my mind the first time I read it.
In this thread are the only examples seen describing this phenomenon that employ qualifiers. “All,” the only way I’ve ever heard this, is an absolute. “97%” is not.
Of course “all” isn’t really as simple as just “all”.
“All” is actually “All for the definition of the condition (blue eyes in this case) the author is implicitly using, and ignoring all exceptions, known and unknown, about which this particular author is ignorant.”
Lotta ways for digging into the details to discover that “all” is only superficially 100%, not actually 100%.
Is this how Isaac got the idea for “Spell My Name with an S”?
Yes, it was
Previous threads on topic (including one started by OP of this thread three years ago) :