We All Begin as One the Same

I know for most people, waking up every morning and looking down a microscope at a developing embryo might not seem that exciting, but for me, it is what I have come to live for.

I’m fascinated, because when you really sit down and think about it, at one point in your existence you were exactly the same as your mother, father, sibling, friend, partner…smelly person next to you on the train.

But not only that, you essentially were exactly the same as your pet dog, cat, rabbit, mouse. As pretty much all mammals.


Because we all started out as a single cell.

And from this single cell, we divided into two cells and then into four and so on. Creating  all of the different types of cells in our body that allow us to function as humans.

You think about how different the liver looks to the lungs or your brain functions compared to your heart. But all these extremely different structures came from that one tiny cell.

Not only that, but this one cell, which essentially looks the same across all mammals gives rise to so many different forms. Just think about how different we are to a tiger or a whale.

But fundamentally, we all started out as the same one cell.

I have the amazing opportunity of tracking the development of a mouse embryo from this one cell until day five after fertilization. I get to see it go from a 1-cell to a 2-cell on Tuesday. By Wednesday it is compacting, and individual cells can no longer be easily recognized. On Thursday, if I’m lucky, I may get some blastocysts. And Friday they start to hatch, a bit like a pimple.

From left to right: Single cells (aka two pro-nuclei cell) mouse embryos, two cell embryos, compacting/morula embryos, bastocysts and hatching blastocysts. Each picture represents one day, Monday to Friday. Source: own photos

And what these mouse embryos are doing, how they are developing is exactly how we humans develop in the beginning. Not as quickly of course as a mouse’s gestation is less than ours, but these fundamental initial process are the same.

Now I may be a little weird, thinking this is fascinating and all. But even if you don’t, and you come away from reading this and think ‘what a crazy’, you have to admit, the pictures are pretty cool.


3 Responses to “We All Begin as One the Same”

  1. Glen Bain says:

    You’re only a crazy if you don’t find this interesting and amazing as far as I’m concerned. I still refuse to admit that I was once the same as the smelly person on the train though!

  2. Rebecca Wilson says:

    It is well into the differentiation I would say. I don’t really work with embryos past the 5 day stage, 1. because it gets harder to culture them unless you put them on an outgrowth plate and 2 when you put them on an outgrowth plate they spread as they would during implantation but we are not quite at the stage of then creating a little mice on a dishes.
    I would guess neurulation and somitogenesis which is still at the very beginning of differentiation would probably be when you can start seeing minor differences. But even at these stages it is still very hard to tell a difference.
    I wish I could provide a more conclusive answer, may have to do a bit more reading and get back to you.

  3. Andrew Katsis says:

    Nice set of photos, Bec! Like you, I’ve always found it amazing to think that everything – every single little instruction – needed to make a human is present in that tiny little zygote. While I’m not as enamoured with microscopes as you are (that’s why I’m in animal behaviour), I did enjoy tracking the development of a chick embryo in Developmental Biology last year. At what stage of development can you distinguish a human embryo from, say, a mouse?