Can you explain the distribution of egg yolk genes in the animal kingdom? Evolution for example would say fish do not have egg yolk genes because they live in a soup of nutrients. Egg yolk was a later development that provides nourishment unnecessary to animals living in the water.
This would also explain why humans do have broken egg yolk genes that could not function. Our egg yolk genes are vestigial structures that point back to ancestors who did not yet have lactation (milk) nor live in a watery soup.
Additionally, it explains why amphibians only have 1 egg yolk gene. Though amphibians live on land they need to remain near water and thus must have a ready supply of water/ nutrient soup for many reasons and only a single egg yolk gene is sufficient. Additionally, we would expect the first animals with egg yolk genes to have fewer genes.
This would explain why reptiles have 3 egg yolk genes. Once they had a more dependable supply of egg yolk, they could live further and further from the nutrient soup of the water that fish and amphibians require. All descendents from reptiles should then have 3 egg yolk genes or remnants thereof, and both mammals and birds do have them.
Furthermore, the most primitive mammals, mammals that don't even have teats do lay eggs and because they lactate they don't rely on their egg yolk genes as much as reptiles. Therefore, 2 of their 3 egg yolk genes are no longer functional - at all, even though they still lay eggs.
The next most primitive mammals, which only have a rudimentary placenta, but do have teats and live birth - the marsupials, do not have any functional egg yolk genes. The genes are still there, but they do not function at all.
Finally, in the most recently developed mammals, we find all the evidence of recent development. Their placenta is more advanced, they have teats, and their egg yolk genes are completely nonfunctional.
If any of these details had occurred in any other order - fish with live births or reptiles with teats, it would not have fit the predictions of Darwin long before genes were even discovered. But in essence, all genetic discoveries ever made -millions of them -have all fit a pattern similar to these few genes mentioned here. Every single one.
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