Because hammerhead sharks give birth to live young, studying their embryonic development is much more complicated than harvesting some eggs and watching them develop in real time.
Early human development is a complex, multistep process that’s even more complicated to study in the lab. Models made from stem cells avoid some of the trouble with using real human embryos.
Of the many qualities that make the zebrafish a model organism, the fact that it shares 70% of the genes humans have makes it an ideal candidate for developmental biology research.
Human embryos are far more likely to die than come to term, an evolutionary trait seen across species. Laws granting personhood at conception ignore built-in embryo loss, with potentially grave consequences.
Unlike humans, many animals are able to regenerate their limbs after losing them. Giving the body the right conditions for regrowth might allow people to recover lost limbs as well.
Genes that are thought to play a role in how the SARS-CoV-2 virus infects our cells have been found to be active in embryos as early as during the second week
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