Could you elaborate on your last statement? You're much better educated about this than I am, so I'm curious to hear more of what you have to say on the matter.
The developmental bio bit? I don't want to go too much into it cause it is a little off topic, but I will be brief and you can PM me about anything else. I will concede that we might be having a semantic disconnect, but presuming we are not, you have severely underestimated the complexity and sophistication of insects (which by extension I am assuming will stand in for all non-human animals), or severely overestimated that of humans. There is remarkably little variation in complexity across higher eukaryotes. Variation tends to come in matters of scale and timing.
-To grab the example on hand (since I am currently slacking off from preparing my presentation on it
) there is so much homology between the human and drosophila brain function that we can express mutantHtt or alpha-synuclein within the drosophila brain, generate the symptoms of Huntington's or Parkinson's respectively, and perform drug trials to determine treatments in humans.
-The study of apoptosis grew out of observations of C. elegans, a roundworm that has 18,424 protein coding genes, which is not very far off from your ~20,000 protein coding genes. One actual benefit of the human genome project was that it finally put to rest the human genomic super-complexity nonsense. And if you really care about raw genome size (coding and non-coding), flowering plants are more complex by at least an order of magnitude.
-If functional complexity and sophistication were a meaningful rubric, bacteria have significantly more complex and sophisticated metabolisms than any
With rare exception humans share a large degree of structural and functional organ homology with other animals, a proteomic functional homology, and an almost complete functional gene homology. The same biochemistry happens in all of us, the same building blocks are manipulated in the same way, to result in similar functions. Nothing about our systems is particularly more complex.
What makes humans (and indeed any other lifeform) unique is what is expressed and when. The embryo is significantly less complex than any organism, because it is largely undifferentiated and does not even have basal components of all systems. The fetus is more developed, but still lacking in a great deal of functional sophistication (which is why it can't live outside the mother). The born human is quite complex and sophisticated, in almost all ways as complex as the adult (there is still a bit of neural and immune development to be done), which is to say: not that much more complex than an ant
So that wasn't as brief as I would have liked, but: It is incorrect to describe a fetus as largely more complex or sophisticated than other animals, it is absurd to describe it as "infinitely" so. It is correct to call a fetus closer to a human than an ant. Although, the same is not true about a human embryo depending on the stage of embryonic development. Which is why, incidentally, I find the idea of being against embryonic stage abortion confusing. And as we see from the CDC data the majority of abortions are of embryos, not fetuses.