excerpts from an interview with an evo-devo researcher:

* everything said here should be questioned and researched independently - it's just a friendly conversation my lecturer videotaped with a colleague.

"primitive vertebrates" - lamprey and hagfish.

- the lamprey is a jawless fish. it was found that it has genes that in other species are responsible for the appearance of jaws.

when talking about genes that are "responsible for the appearance of jaws", they are not the osteoblasts or the ones that regulate the mineralization of the bone. they are genes that regulate the development of a certain area of ​​the body.
found in the lamprey, yet it has no jaws, so what are they regulating?
they regulate something in the front of the mouth.
at the next stage, when the jaws appear, they will function in this task.

(...) this is exactly the essence of evo-devo. we see the same genes used in many, many different roles.

for example, SHH, BMP.
found in bone development. yet it is also related to the development of muscles, skin, eyes, etc.
the gene does something specific, but its function depends on the context

similar to exaptation (a shift in the function of a trait during evolution) - this happens at the molecular level.

another example - kidney development -

in embryonic development there are three kidneys - pronephros, mesonephros, (opisthonephros,) metanephros.
early embryonic state in vertebrates, later embryonic state in vertebrates, (the functioning kidney in fish and amphibians,) the functioning kidney in reptiles, birds and mammals.

is the nephridium found in the left part of the mouth of the amphioxus (nephridium - an invertebrate organ performing a similar function ro the kidney) - in the front of the head - is it homologous to our kidneys or not?

relying on embryonic development - it develops from the ectoderm and the mesoderm. (our kidneys develop only from the mesoderm)

in 1999 - first article published about a gene called PAX2, the first renal marker of the pronephros in the models tested.
it can be seen in the chicken, at the border between the head and the neck, the middle of the 6th somite.
somites - mesodermal segments of vertebrate embryos that become the vertebral column, skeletal muscle and dermis.

we can find this gene in the amphioxus, in the nephridium that appears in the head.

in 2006, the second gene appears which is our marker, LIM1, both appear in the amphioxus.

at the deep homology level - hatschek's nephridium is homologous to our kidneys.

(...) the kidney leaves the head - there are no more kidneys in the head (from an evolutionary point of view, in vertebrates).
we look at the lamprey again, the same genes are expressed in it, in a kind of nephridium, in the 6th somite, same as the chicken.

a line is formed - the 6th somite, which allows what is above it to develop into a head, and below it to develop into a kidney.

(...) we take the embryonic development of one animal, we can learn from it about the general evolutionary process, about the development of vertebrates in general.

the field of molecular evolution, which belongs to developmental biology, found that the regulation mechanisms of the development of these forms - there is a fundemental level, a level of genetic regulation, which is common to all processes.

you can ask - how is it that we are not all the same (appearance, function) if the regulation is the same?
within the regulation we see the small nuances that lead us through gradual changes from a state that is very general.

the early stages of embryonic development show high similarity between different species. they are tightly regulated by conserved genes becuase of how crucial they are to the growing embryo.
variation becomes possible as the fetus grows and the changes become less lethal.
the main differences appear in the periphery of the development process.

also mentioned during the interview: tunicates and not cephalochordates are the closest living relatives of vertebrates.