I left this a little bit unanswered in the last post.
I explained how pregnancy is so long in humans mainly due to our brains. By that logic a lot of people might assume neurulation is the most important.
I also mentioned that one of the biggest problems with premature births is poor lung development. So that might suggest that organogenesis might be the most important.
But no it’s Gastrulation.
It is not birth, marriage or death which is
the most important time in your life, but Gastrulation.
– Lewis Wolpert, 1989
That is because our entire life will be more or less defined by what happens at this stage. It only lasts a day or two, but it organises your entire body into the right components. From this point on, your body knows what it is and how it is meant to work. This is where development really starts. If it went wrong, we would most likely not survive as different parts of our body would end up in the wrong place.
If neurulation or organogensis goes wrong, we could be seriously disabled, but it won’t be as badly as if Gastrulation went wrong.
Granted in all cases stillbirths can happen.
Cleavage, although the first and most basic stage, is not as important. If cleavage goes wrong, we get three primary outcomes:
So there you go, that is why Gastrulation is the most important.