From: rokimoto557@gmail.com   
      
   On 12/29/2025 11:07 PM, MarkE wrote:   
   > On 30/12/2025 3:55 pm, MarkE wrote:   
   >> On 30/12/2025 1:49 pm, David Canzi wrote:   
   >>> On 12/27/25 06:27, MarkE wrote:   
   >>>> On 24/12/2025 7:27 am, John Harshman wrote:   
   >>>>> You're just avoiding the question, which I will repeat:   
   >>>>>   
   >>>>> But how many genetic changes do you think were necessary to turn   
   >>>>> the human-chimp ancestor into a modern human? Give me a ballpark.   
   >>>>>   
   >>>>   
   >>>> Much more than "a few thousand", i.e. orders of magnitude.   
   >>>   
   >>> Can you say something actually quantitative, ie. something of the   
   >>> form x plus or minus y percent, and if you do this, can you show   
   >>> how you calculated it?   
   >>>   
   >>> It's your job to justify your claim.  If you haven't made the effort   
   >>> to justify your claim, nobody owes you the effort to justify their   
   >>> non-agreement with your claim.  You're freeloading.   
   >>>   
   >>   
   >> I acknowledge that I can't put a number on it. Partly because of a   
   >> lack of expertise/ability, and partly because, well, who can? But that   
   >> does not mean it doesn't exist.   
   >>   
   >> See my more recent post "The information problem", where I attempt to   
   >> grapple with this some more.   
   >>   
   >> I think it's a fascinating area, even setting aside the creation/   
   >> evolution arguments. A single fertilised egg dividing and   
   >> exponentially multiplying to create an new and unique human should   
   >> always astonish us, no matter how much we may understand the processes   
   >> involved.   
   >>   
   >> What do you think?   
   >>   
   >> _______   
   >>   
   >>   
   >> FROM ONE CELL TO A HUMAN BEING: AN OVERVIEW OF THE PROCESS AND ITS   
   >> MYSTERIES   
   >>   
   >> *Fertilisation* begins when a sperm and ovum fuse to form a single   
   >> cell: the *zygote*. In that moment, a new, genetically unique human   
   >> organism exists. Yet nothing visible distinguishes this cell from   
   >> countless others. What follows is one of the most extraordinary   
   >> processes known in nature.   
   >>   
   >> ---   
   >>   
   >> ## 1. Exponential division without growth: cleavage   
   >>   
   >> Within hours, the zygote begins dividing: 1 cell becomes 2, then 4, 8,   
   >> 16, and so on. These early divisions, called *cleavage*, are   
   >> remarkable because the total size of the embryo does not increase.   
   >> Instead, the original cytoplasm is partitioned into ever-smaller cells.   
   >>   
   >> Key features:   
   >>   
   >> * Division is rapid and tightly synchronized.   
   >> * Cells remain enclosed in the original outer membrane.   
   >> * The embryo reaches ~100 cells in a few days.   
   >>   
   >> *What is striking:*   
   >> All cells initially appear equivalent, yet they are already on   
   >> trajectories that will lead to radically different fates.   
   >>   
   >> *What we do not fully understand:*   
   >> How early asymmetries—subtle differences in molecular concentrations,   
   >> mechanics, and timing—bias later cell fate decisions with such   
   >> reliability.   
   >>   
   >> ---   
   >>   
   >> ## 2. Self-organisation and implantation: the blastocyst   
   >>   
   >> After several days, the embryo reorganises into a *blastocyst*—a   
   >> hollow structure with:   
   >>   
   >> * an *inner cell mass* (which will become the body),   
   >> * and an *outer layer* (which will help form the placenta).   
   >>   
   >> The blastocyst implants into the uterine wall, establishing a   
   >> biochemical dialogue with the mother that allows pregnancy to continue.   
   >>   
   >> *What is striking:*   
   >> This organisation emerges without a central controller. Cells “decide”   
   >> their roles through local interactions, gene regulation, and physical   
   >> constraints.   
   >>   
   >> *What we do not fully understand:*   
   >> How global structure arises so robustly from local rules, and why   
   >> implantation succeeds or fails so often despite apparently normal   
   >> embryos.   
   >>   
   >> ---   
   >>   
   >> ## 3. The body plan appears: gastrulation   
   >>   
   >> Around the third week, the embryo undergoes *gastrulation*, often   
   >> called *the most important event in your life*. A simple sheet of   
   >> cells folds and rearranges to form three foundational layers:   
   >>   
   >> * *Ectoderm* → nervous system, skin   
   >> * *Mesoderm* → muscle, bone, blood, heart   
   >> * *Endoderm* → gut, liver, lungs   
   >>   
   >>  From this point onward, the basic body axes—head to tail, back to   
   >> front, left to right—are established.   
   >>   
   >> *What is striking:*   
   >> A consistent human body plan emerges from dramatic cellular movements   
   >> that look, under a microscope, almost chaotic.   
   >>   
   >> *What we do not fully understand:*   
   >> How genetic instructions, chemical gradients, and mechanical forces   
   >> are integrated in real time to yield precise, repeatable anatomy.   
   >>   
   >> ---   
   >>   
   >> ## 4. Differentiation and organ formation: organogenesis   
   >>   
   >> Cells now differentiate into hundreds of specialised types and   
   >> assemble into organs. Neural cells wire themselves into circuits.   
   >> Blood vessels branch through tissues. The heart begins beating while   
   >> still forming.   
   >>   
   >> Cell numbers increase exponentially, eventually reaching *tens of   
   >> trillions*, yet:   
   >>   
   >> * proportions are maintained,   
   >> * left–right symmetry is mostly preserved,   
   >> * errors are detected and corrected.   
   >>   
   >> *What is striking:*   
   >> No cell “knows” the whole plan, yet the whole plan reliably appears.   
   >>   
   >> *What we do not fully understand:*   
   >>   
      
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