Vitellogenin and Common Ancestry: From Egg to Placenta


(system) #1
How did egg-laying creatures evolve into creatures that have "live births"?
This is a companion discussion topic for the original entry at https://biologos.org/blogs/dennis-venema-letters-to-the-duchess/vitellogenin-and-common-ancestry-from-egg-to-placenta

(Dcscccc) #2

“Why such (repeated) transitions within reptiles is viewed as trivial, but such a transition within mammals would be “notoriously difficult” is not explain”-

i think because its need a new genes or structures. i dont think its the case with the “dual mode lizards” because they have this ability to switch between the 2 mode just from the beginning. the fact that this transition happaned about 100 times in the past (according to evolution) only in lizard support this claim.


(Dennis Venema) #3

Hi dcs,

The transition from egg laying to live birth has happened numerous, numerous times in skinks, lizards, fish… it’s not a phenomenon seen “only in lizards”. It seems to be a very easy transition to make.


(Dcscccc) #4

hi dennis. according to this paper about 115 times (from a total 150) in squamate reptiles only(snakes and lizards):

so its a far from a chance that only in this group its happaned. if they have this dual ability then it cant prove evolution. another option may be indeed that its a degeneration. and therefore dont need any new structure.


(Dennis Venema) #5

Do you even read what you post?


(Dennis Venema) #6

Also, here’s the point you need to understand: evolution works through tweaks and minor modification of previously existing structures and mechanisms - it’s called exaptation. In this case there was no need for “new genes” or “new structures” - just modification of prior structures.


#7

Dennis, I don’t think it’s about reading. It’s a style of argument by references with no overall synthesis of a bigger picture.


(Dcscccc) #8

yes. i actually refer to the fact that about 80% of those cases happaned in a specific group of species. what doest it may mean? that those species have the ability to switch between 2 modes.

if its indeed true then its actually support the creationists claim that its only a variation. all we need is just to change the regulatory of the egg formation\degeneration. or something close to that.


(Dennis Venema) #9

Evidence for the ease of the transition and the exaptation of similar prior structures cuts across all groups that have shifted to viviparity - including for mammals. Creationists are claiming the mammal transition is inexplicable, but the transitions in other groups are trivial. You can’t have it both ways - unless you can provide a decent reason why the mammal transition could not have happened, despite the ease of the transition we see (repeatedly) in other groups.

This is, in a nutshell, the problem with “baraminology.” It cannot be made into a coherent discipline. YECs posit that there was massive, massive speciation and huge morphological change in the blink of an eye (within a 1000 years of the flood) - but that somehow this rapid evolution could not, even in principle, cross their pre-determined boundaries. As one example, the amount of DNA diversity within baramins is HUGE - even within mammal baramins. Yet YECs confidently tell us that humans and chimpanzees cannot be related even though they have DNA which is much, much more similar to one another than for other mammals within a baramin (and thus descended from a common ancestor on the ark). So, on the one hand they posit massive change, and on the other hand they must decree certain groups as somehow separate even though they hold to a model that easily produces far more change at the DNA level on a hundreds-of-years timescale.


(Dcscccc) #10

it may be possible that some mammals do have the ability of “dual mode”. as some mammals also have a functional vit gene.

true. because it’s not just about genetic variation (neutral mutations in the noleculalr clock) but about a new complex structures. so even if the different between chimp and human was about 300 bases (but we need all of them at once) it doesnt mean that we can move from one to another step wise. the type of different that’s what make it different.


(Doug B) #11

David Attenborough’s “Life of Mammals” shows the transition on the mammalian side in marsupials. That series is excellent–much like these posts!


(Chris Falter) #12

This is interesting. Which mammals? What is your source?

That’s another interesting statement, and again it is presented entirely free of evidence. It would take a lot of hard analytical work to validate this statement. Are you basing your statement on your own empirical investigation, dcs? Or are you relying on the published empirical observations of a biologist/geneticist?

@dcscccc - So you would agree with the statement that mammals evolved from egg-laying reptiles?


(Dennis Venema) #13

Egg-laying mammals retain functional vitellogenins - i.e. the platypus and echidna. They use them in exactly the same way other egg-laying species do - to form their egg yolk.


(Dcscccc) #14

try this one:

no. im just open to the possibilty that some mammals have the ability to switch between the 2 modes.


(Dennis Venema) #15

Hi dcs,

This is another case of you not understanding what you are posting. That paper describes how new genes arise - but they don’t arise from nowhere. These “new” or “de novo” genes have highly similar sequences that are not genes in related organisms. If you look at the table with average substitution rates you’ll see numbers on the order of 30-70 per 1kb (thousand base pairs) when comparing them between species. Note that 930/1000 = 93% identical.

So, what we see for “de novo” genes is that they don’t arise whole cloth at once - they arise from small changes to pre-existing, near-gene sequences.


(Dcscccc) #16

hi dennis.

first- many of those genes may be false genes. even according to the paper:

“De novo genes showed characteristic promoter and splicing signals and were expressed in a consistent manner across different individuals. However, they had very weak purifying selection signatures in general. This is interesting because it means that even if these genes are expressed in a stable manner, many of them are likely to lack functionality and thus can be considered protogenes”-

so they may be “background noise”.

secondly- the chance to get a functional protein from a random sequence is extremely low even according to evolution. so even evolutionist cant agree that those genes are just evolve by chance from a random sequence. its no more the step wise model for a new protein but a big jump in the sequence space (20^100 for a small protein).

i just gave this paper to show that there is many unique genes among a lot of species. and only one gene that is unique to human is to much for evolution.

not according to the paper (at least for hominoid):

“we used BLAST-based sequence similarity searches [49] to identify the subset of de novo genes that could have originated in human, chimpanzee, or the common ancestor of these two species since the divergence from macaque (hominoid-specific genes). These genes lacked homologues in other species after exhaustive searches against the transcript assemblies described above”

"


(Dennis Venema) #17

Again, you do not understand what you are reading. Let me try explain…

The comparisons are against transcript assemblies - i.e. transcribed regions, i.e. genes. The authors of the paper want to be sure that they are looking at new genes, so they are looking for homologous genes (transcribed regions) in other species.

The de novo genes they find are not transcribed as genes in other species. There are, however, sequences nearly identical to the transcribed genes in those other species. Not finding a homologous gene is not the same thing as there not being any sequence like that in other genomes, as you are claiming.


(Dennis Venema) #18

Look back at my recent post on nylonase - it’s a truly “new” protein, “from nowhere” with respect to its amino acid sequence, it’s 392 amino acids long, it folds beautifully, and it’s a functional enzyme that came under natural selection. Sequence space for functional proteins is not a problem for evolution.


(Dcscccc) #19

. yep. i have notice it just now. but where they discuss about a match sequence in other species that lack those transcript?

but remember that even several amino acid can be functional. it doesnt mean that you can go from several amino acid to a complex biological systems like a blood clothing or a ttss.how many amino acid from the 392 need to digest a nylon? i think that not more then one or two.


(Dennis Venema) #20

All 392 amino acids are part of the nylonase enzyme - they form its 3D structure and folds, which are necessary for its function (digesting nylon).

Also, systems like the blood clotting cascade are not proposed to have flashed into existence from nothing, but rather, the evidence we have supports the hypothesis that they were built up over time.