>Less than a month after four towering dams on the Klamath River were demolished, hundreds of salmon made it into waters they have been cut off from for decades to spawn in cool creeks

Do we understand the mechanisms of this "genetic memory" (my words, no idea if its accurate or if there is a better word for it)? Butterflies knowing where to fly even though it was their grandparents that last did it - eels traveling thousands of miles to breed in a place theyve never seen - countless bird migrations - even something as simple as how it takes a human baby 12-18 months to walk but many animals walk as soon as they are born. I would love to understand better how this knowledge is inherited

Salmon have no "genetic memory" - if you release baby salmon from a hatchery that were bred from adults caught elsewhere, they remember where they were released- not where they are genetically from-, and swim back to the area of the hatchery. It appears to be regular memory learned from experience. It is believed to be mostly chemical sensing, e.g. specific smells that they are remembering and returning to.

Salmon are not 100% effective at making it back to their birthplace, and some small fraction stray randomly- which is what allows them to populate new areas and re-populate others where they were wiped out. This article isn't about a lot of salmon - only hundreds, so this is probably the amount that would naturally stray to this region from others, with or without a healthy returning population.

For example, some ~120k chinook salmon returned to the Columbia river this year, so if 0.01% of them strayed to the Klamath river, you'd get about this many.

Looking at salmon research literature I found a study[0] with the following conclusion:

This study provides convincing empirical support for fine-scale local selection against dispersal in a large Atlantic salmon meta-population, signifying that local individuals have a marked home ground advantage in reproductive fitness. These results emphasize the notion that migration and dispersal may not be beneficial in all contexts and highlight the potential for selection against dispersal and for local adaptation to drive population divergence across fine spatial scales.

Seems like it might simply be that they go where they adapted to thrive.

[0] https://www.science.org/doi/full/10.1126/sciadv.aav1112

If some salmon group had been simplistically "programmed" to go up these waters, they would have been trying and failing to go up the river during the entire time the dam was there and so likely wiped out as a group/subspecies.

It seems like the fish would have to have had some kind of way to test if the river lead to adequate spawning grounds. And if they had that, they wouldn't really need any memory of any given river.

> Do we understand the mechanisms of this "genetic memory"

I don't think there is particular evidence for "genetic" memory here. The salmon were already further down river, they just kept swimming upstream. While most salmon do return to the place of their birth, a small percentage always stray, which is how salmon are able to colonize new habitats and survive things like ice ages.

This news is about the end of a dam removal project. I believe this is also the end of the oldest dam removal project. The Klamath and IIRC the local tribes were the original test for salmon restoration/dam breach projects in the PNW, and subsequent programs are copying their success.

One of the things that makes salmon ladders more effective is introducing artificial noise of falling water. Turns out when salmon find themselves in still water they head for the sounds of the inflow, which dams either don't have, or are from spillways that the salmon cannot navigate.

Most salmon want to go back exactly where they are born, and on a three year cycle (or at least, that's the pattern on the Klamath). So if you were to introduce hatchery salmon in 2024, in 2027 and every three years after you'll have a full run, and only a small number of fish in the remaining years. Which probably isn't good for genetic diversity. So you end up having to stock at least 3 times, or just wait and see what happens.

NOAA page listing the history of work on this river (could use a timeline):

https://www.fisheries.noaa.gov/west-coast/habitat-conservati...

Whites Gulch Dam, ca 2008:

https://www.fisheries.noaa.gov/feature-story/building-networ...

> how it takes a human baby 12-18 months to walk but many animals walk as soon as they are born.

This is because humans are born with, comparably, extremely immature brains. The animals that can walk after birth are born with more mature brain development than humans are born with, so they are capable of walking.

https://www.livescience.com/9760-study-reveals-infants-walk....

There could be an environmental feature they prefer in that spot.

Edit: the article mentions lower concentration of harmful algae and a cooler temperature.

The book Bird Sense by Tim Birkhead covers birds’ magnetic sense in Chapter 6. Research has demonstrated that seabirds have a magnetic map and compass that they use to navigate home, but it doesn’t discuss how this knowledge is inherited.

I believe Salmon use a similar mechanism, but it might be supplemented with chemical signatures. For Salmon, it’s possible that they genetically inherit the capability but learn the location at birth.

these are hatchery fish; they were born on the klamath and they're returning to it. the only difference is that now they can make it to tributaries and spawn naturally, instead of being collected and having their eggs harvested and fertilized by humans back at the hatchery

I was also curious about how a popular beaver [1] was raised by humans and "instinctively" knew how to build dams.

[1] https://www.youtube.com/watch?v=DggHeuhpFvg

It's not a genetic memory. They return to the place they were born. This is probably based on the "scent" of that place, and maybe other factors.

Some percentage either accidentally or deliberately go up a different river, which is how the species spreads. That's very likely who this story is about.

I know it's going to sound like a bunch of hooey, but information really is the most intrinsic element of all aspects of this universe, especially when it comes to life. The life force is a thing that is interrelated with our physical bodies, but is not the physical body. It's just like the zen concept of "Not 2, not 1". Our minds have the same relationship with our brains. They're not separate, they're not the same; they're interrelated.

That we can't "see" the other side of the connection with our science is due to our science being built with our physical world's constituents (matter & energy), thus those other dimensions are immeasurable with our science's tools. Rupert Sheldrake speaks of this when he says that the genetic code's protein construction genes do not and can not account for the resulting organism's shape. That coordinated construction requires a separate guiding force. That interrelationship is similar to the "memory" that creatures such as salmon have, which is intrinsic to their entire being, not just their physical body, which is only half of our being's totality.

> even something as simple as how it takes a human baby 12-18 months to walk but many animals walk as soon as they are born.

That's just a matter of muscular development. Human babies are born early; I believe this is usually attributed to the difficulty of getting the head through the birth canal.

My 100% speculation is emergent behaviour from the brain itself. Same way human interactions have remained largely the same over thousands of years. Also, we don't notice the salmon that swam up dead ends elsewhere.

The story about eels is especially fascinating. I was told in my fishing course they can even get across small patches of land to continue on their journey. I did not bother to fact check it though.

Human babies physically cannot walk. It’s not merely a knowledge check.

Pretrained brain modules aren’t the most surprising thing. Humans have plenty of pre trained behaviors, some of which kick in a while after birth.

The simplest answer in this specific case is that there is no genetic memory involved, and salmon will just swim upstream into any fresh water stream they come across.

> Do we understand the mechanisms of this "genetic memory" (my words, no idea if its accurate or if there is a better word for it)?

It’s not actually a memory that gets encoded in genes.

It’s a tendency to behave in certain ways as influenced by combinations of genes

Ancestors who had the same tendencies, drives, and preferences would have some similar behaviors, resulting in some of them going toward the same places.

So not an actual memory that gets inherited, more like personality traits (but in a more general sense) that lead to similar outcomes.

There is a field of epigenetics which studies heritable changes in cells that occur without DNA alteration, but these signals are much simpler than memories and not a mechanism for carrying memories across generations. A lot of pseudoscience has been written around epigenetics right now so you have to be careful about where you source info on this.

magnets...

but I am not even kidding. they include a tiny bit of magnetic material in their ear. but it must be a genetic construct that informs them what to do with north, they use it to move to particular undersea canyons out in the ocean they have never been to.

It is a mystery, like lots of other phenomena that science fails to explain. Personally I think all those creatures are much more intelligent and aware than we give them credit for. Viewing these creatures as simple automatons is as silly as viewing humans as such.

I’d assume that evolution in salmon is just not fast enough to catchup with the dam.

EDIT: I don’t mean that as a joke. I think on the timescale of evolution the dam was never there.