Thread by @soychicka

Until a fetus reaches ~28 weeks, it doesn't feel pain.

What is pain? You know what it feels like, but from a functional perspective, it's a switch in a circuit, meant to cause you move away from a harmful stimulus - like a hand on a hot stove, or a chemical...

And pain also helps keep you from engaging in normal activity that adds further injury to an existing wound.

How the circuit works:

1) nerve cells in epithelial tissue, like skin, called "nociceptors" have sensors that detect harmful stimuli, like heat, chemicals, pressure/impact

2) when switched on, nociceptors release some molecules called Calcitonin gene-related peptide (CRGP) & Substance P which pass through to receptors, dilating blood vessels, signaling there is a painful stimulus, and mediating repair to any local damage
aimovig.com/what-is-aimovi…

3) Those messages go through two circuits -

first, some messages reach the spinal column and instantly switch on the motor circuit, leading to muscle contraction and movement away from the stimulus - this is a "reflex"

second, other messages travel up the spinal column, through the brain stem, into the thalamus, then out to the cortex, where pain is finally perceived, and long-term behaviour can be modified.

Think back to middle school science:

The brain stem is like the thermostat, helping the body maintain homeostasis (breathing, temperature) - like a proprietary processor with hard-coded software

The limbic system (incl the thalamus) receives and pre-processes sensory input...

And the cortex is where information is processed and assigned meaning - it's where perception and free will reside.

IOW, it's where our humanity is.

Now, take out any of the connections in that circuit, and you don't have the sensation of pain.

And if you look below, you'll see that the connection between the Thalamus isn't made until at least 24 weeks.

Now, this makes total sense from an evolutionary perspective:
fetuses develop so that viability is possible as early as technically possible.

If the reason we perceive pain is to modify our behaviour to prevent injury, what benefit would a pain provide a fetus, existing in a closed environment, with a low probability of encountering unintended external stimuli?

If something showed up, they wouldn't be able to escape..

So deferring the use of resources to generate connections pain off to later during pregnancy, closer to when a fetus has a chance of surviving make sense from an evolutionary, resource-based perspective.

Point blank, until a fetus's lungs are developed enough to breathe, they are not viable. And until the connections between the cortex and the lower brain are established, the fetus is not capable of sensing pain, thinking...

and, TBH, I'd say should be considered no more a 'person' with its own legal rights than an axolotl is a person.

If you want extend personhood to animals, that's a frame where restricting abortion earlier than 20 weeks *could* make rational sense -

but if God wanted a 6 week old fetus to have a "soul," or full personhood from conception onward, the time frame for connecting up the cortex would have taken priority over other organ systems.

But she didn't - and there's a reason that medicine considers 24 weeks to be the point of inflection between a miscarriage and a stillbirth:

It's because a fetus can not be considered a living person until cortical function has begun.

[ I've shorthanded a lot of stuff here because Twitter. Ask for clarification before you hate on anything. ]

[ But, TBC, the Heartbeat bills are damn stupid. ]