How do genes tell a baby turtle to follow the moon to the ocean after birth?
In: Biology
The instinct they have is “move toward the light”. When they hatch the moon shines off the ocean and that direction is brighter than the darkness of plants and dunes at night. The light is attractive and they move toward it. Moving toward light is one of the simplest possible instincts, even plants can do it…heck even some single cell organisms do it.
They don’t follow the moon. They follow light. It’s just that moonlight reflects off the ocean really well.
There’s a problem here in that now there are other light sources- namely cities. So you’ll get baby turtles following lights across busy streets instead of going down to the ocean.
Responses to certain stimuli are “hard-wired”. This happens in humans too. Genetics guides how pathways develop in the brain (idk if this is even well understood yet, lots of brain stuff is poorly understood and a lot of theories about even well known neurological diseases are just educated guesses).
Take a cat for example. They naturally develop a response to certain movements indicative of prey. Nobody taught them that. Just put a prey-like thing in their field of view and they will reflexively look at it and you can see their pupils reflexively dilate too. The turtles are likely hard-wired to follow the light.
Here is how i imagine it, the turtles that where’nt born with a mutation to look at the “moon” or hear the waves went in a wrong direction and died. The ones that did went on to reproduce. This mistake is a tool to evolution and its the way 90+% of “adaptations” work. I say adaptations with quote marks because its a bad word to describe success by chance, witch is how it really goes. The other % of traits are random mutations that arent bad for you and they stick around just because of aestetics or because some other trait was so good that that one didnt matter for the mating process (silly example: monobrow, i mean what happened there, i guess the guy had amazing hunting skills so he got some ass dispite the face).
Daniel Dennett discusses the analogous behaviour of frogs eating flies to illustrate the (under)determination of meaning. In brief, it seems that frogs don’t really see flies; they just detect black blurs moving in front of them. But changes in circumstances (such as an invasive species of fly arriving) cause adaptive responses in frogs, so changes in meaning emerge (not in individuals but across the species) as nature selects the optimal fly detectors. If sea turtles don’t go extinct too quickly, we will see a similar recalibration of their instincts, as meaning and function distinguish between moonlight and boardwalks. (See Intuition Pumps, ch. 47.)
I see a little gap in what people are saying, so I’ll try to explain the process of “hard-wiring” others are mentioning in a simple way:
When the embryo is just a couple of cells, the DNA is being read by a long process that eventually works as like an instruction manual on how to build all sorts of different proteins. Proteins do everything and anything kinda, so they can act as signal molecules that tell all the cells how to develop and such ie there are cells that give off more of a certain protein that tell the cells around them to start making arms, legs etc. In the process of building a body from scratch, these proteins also dictate how the brain works, and what chemical stimuli the brain should respond to. One of those signals is the light from the moon, or tragically, light posts, flashlights, etc. The light hits their eyes and sends chemical/electrical signals to the brain which is primed to send the turtle in that direction (whether or not that’s the ocean) at that early(ish) stage in the brain’s development.
Edit: For those asking for more details and/or a more authoritative or generalized explanation of some of this, u/PotatoBasedRobot shared [this](https://www.reddit.com/r/askscience/comments/irxncu/how_does_a_cell_know_what_to_become_if_they_all/g54ffw9?context=3) link to another reddit comment I found to be informative and clearly written.
Because the ones who randomly mutated that gene originally survived more. Reproduced more. That’s how all of it works. Why do people think genes are sentient in 2020
Same way that your genes tell you that sugar is tastey, girls are pretty, and sex feels good.
There’s patterns in the genes which tell the cells in your brain how to get made. Brains are not entirely blank slates where everything has to be learned. Some bits are hard-wired or baked-in. We’re specifically wired to learn languages btw. We’ve got dedicated hardware for it. Some of that also influences things like… behavior, personality, and fight-flight responses. And to go make babies at puberty.
Everyone is getting really in depth with this, but im certain the moon isnt always over the coast of the ocean. Isnt the questioned flawed? What about the baby turtles born on a different coast? The turtles go inland?… Maybe the post should have left the moon out of this?
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