Gary: At one time in history, most people in our western culture believed that human existence began in “the womb” as a tiny miniature version of the infant we see at birth. Little did they know, that in reality, every human starts off his or her existence looking like a fish!
But what should we expect? These people had been indoctrinated for more than a millennia that humans were created in the image of God. But if human beings were created by God, in his image, as the Judeo-Christian holy book says, why on earth did God create human embryos to look like fish? Is God a fish??
Jerry Coyne, biologist and professor, University of Chicago: Well before the time of Darwin, biologists noticed some odd peculiarities when studying how animals develop (embryology) and when studying the similarities and differences in the structure of different animals (comparative anatomy) that did not make sense. For example, all vertebrates [creatures with a spinal column] begin development in the same way, looking rather like an embryonic fish. As development proceeds, different species begin to diverge—but in weird ways. Some blood vessels, nerves, and organs that were present in the embryos of all species at the start suddenly disappear, while others go through strange contortions and migrations. Eventually, the dance of development culminates in the very different adult forms of fish, reptiles, birds, amphibians, and mammals. Nevertheless, when development begins, they look very much alike.
It was [Charles] Darwin who reconciled these [odd peculiarities] found in embryology that filled the textbooks of his time, and showed that the puzzling features of development suddenly made perfect sense under the unifying idea of evolution. Embryology rises greatly in interest, when we thus look at the embryo as a picture, more or less obscured, of the common parent-form [ancestor] of each great class of animals.
…Why do different vertebrates, which wind up looking very different from one another, all begin development looking like a fish embryo? Why do mammals form their heads and faces from the very same embryonic structures that become the gills of fish? Why do vertebrate embryos go through such a contorted sequence of changes in the circulatory system? Why don’t human embryos, or lizard embryos, begin development with their adult circulatory systems already in place, rather than making a lot of changes in what developed earlier [in fish and amphibians]? And why does our sequence of mimic the order of our ancestors (fish to amphibian to reptile to mammal)? As Darwin argued in The Origin, it’s not because human embryos experience a series of environments during development to which they must successively adapt—first a fishlike one, then a reptilian one, and so on. …[E]ach vertebrate undergoes development in a series of stages, and the sequence of those stages happens to follow the evolutionary sequence of its [evolutionary] ancestors.
…All vertebrates begin development looking like embyronic fish because we all descended from a fishlike ancestor with a fishlike embryo. [As the embryo develops] we see strange contortions and disappearances of organs, blood vessels, and gill slits because descendants still carry the genes and developmental programs of [evolutionary] ancestors. And the sequence of developmental changes also makes sense: at one stage of development mammals have an embryonic circulatory system like that of reptiles, but we don’t see the converse situation. Why? Because mammals descended from early reptiles and not vice versa!
––Why Evolution is True, pp. 73-79
Gary: Creationists must ask themselves this question: Why did God create humans with gill slits?
End of post.