Am aflat de curand de la un biolog din Germania despre cercetarile asupra procesului de fetalizare si retardare (cred ca sunt traducerile adecvate pentru "Fötalisation" si "Retardation"). Totusi, cautand informatii pe internet, am fost surprins de faptul ca nu am gasit mai nimic relevant, in afara poate de acest articol.

Ce presupune insa acest proces? Este practic o alternativa la viziunea neodarwinista asupra evolutiei, care afirma ca organismele evolueaza prin mutatie si selectie. Nu este negata aceasta teorie, in schimb este considerata marginala.

Fetalizarea presupune, din cate am inteles eu, faptul ca-n stadiul de fetus si nou-nascut un organism are trasaturile unui stadiu superior al evolutiei, trasaturi ce se atenueaza pe parcursul cresterii prin procesul de retardare.

Am redat mai jos o imagine in care este reprezentat craniul de Australopitecus, apoi omul din Java, din Neanderthal si, in sfarsit, omul actual. Fiecare pozitie este prezentata ca adult si copil, iar prin intermediul liniilor punctate se urmareste redarea asemanarii cu stadiul adult urmator.



Dupa cum se poate observa, in stadiul de adult maxilarul devine mai pronuntat, in schimb partea anterioara a capului se dezvolta mai putin.

Acelasi aspect poate fi observat si la primate. Mai jos sunt doua imagini, prima compara craniul de fetus, pui si adult la cimpanzeu, cea de-a doua pe cel al unui nou-nascut, al unui exemplar tanar si adult de urangutan.



Inca o imagine care compara dezvoltarea craniului la cimpanzeu (stanga) si om (dreapta):



Apoi, avem o imagine care arata distributia parului la fetusul de gorila, cimpanzeu si om. Se poate observa, mai ales la cimpanzeu, similitudinea cu adultul uman. Restul trupului este lipsit de par, ca si in cazul omului.



Cu alte cuvinte, notiunea de fetalizare indica faptul ca in fetus sunt prezente predispozitiile pentru stadiile superioare de evolutie. Dupa parerea mea, acest concept infirma in mare parte afirmatia lui Haeckel, "ontogeneza repeta filogeneza", de vreme ce in fetus poate fi observat stadiul mai dezvoltat al organismului, care este apoi atenuat prin "specializarea" din procesul de crestere. La om, la care specializarea se manifesta cel mai putin, diferentele fata de craniul fetusului sunt mai reduse, dupa cum poate fi observat in cea de-a treia imagine.

Poate cineva sa dea mai multe detalii despre acest proces, sau sa argumenteze in favoarea sau impotriva lui?

Cum ai tras tu o astfel de concluzie?

Am gasit o prezentare a unei carti care trateaza in detaliu notiunea de fetalizare - daca nu gresesc e cea din care au fost extrase imaginile de mai sus.

Poti gasi acolo ca fetalizarea este tendinta organismului de a pastra forma din stadiul fetal. Cu cat se pastreaza mai mult caracterul sau juvenil (care implica specializarea cat mai redusa), cu atat fiinta va fi mai evoluata.

Un rol important in aceasta viziune o are notiunea de hipermorfoza, care presupune ca, datorita ramanerii mai aproape de stadiul de fetus, anumite organe sunt capabile sa faca un salt calitativ, dezvoltand insusiri noi.

Acest topic a fost editat de mărăcine: 19 Nov 2005, 03:21 AM

O notiune importanta pe care nu am clarificat-o foarte bine - si a carei denumire poate induce in eroare - este cea de retardare. Prin acest termen se desemneaza parcurgerea acelorasi faze de dezvoltare intr-un timp mai indelungat decat in cazul stadiilor inferioare ale evolutiei (care parcurg aceleasi faze intr-o perioada mai comprimata).

Acest proces merge "mana-n mana" cu cel de fetalizare, conducand - prin reducerea gradului de specializare a diferitelor organe - la dezvoltarea aptitudinilor superioare.

De pilda, la mana umana vedem pe de o parte rezultatul fetalizarii, prin faptul ca policarul (degetul mare) dezvolta prin hipermorfoza abilitatea de a veni in sens opus celorlalte degete, astfel ca omul poate apuca obiectele cu mare precizie, iar la intreaga mana se poate observa procesul de retardare, in sensul ca necesita o perioada mai lunga (raportat la lungimea vietii) decat in cazul primatelor pentru a se dezvolta pana la maturitate.

Draga maracine, ai inteles foarte bine despre ce e vorba. Ceretarile despre care vorbesti, cu puii de mari primate cu par pe cap si fara par, comparatia profilelor la puii de cimpanzeu si la om, astea reprezinta cercetari vechi. Asta se cheama neotenie, adica pastrarea caracterelor de nou nascut, embrion la adult ( neotenie si pedomorfism). Ideile, nu chiar in forma asta, vin incepand din secolul al XIX-lea de la Saint Hillaire, care a inventat termenul neotenie. Acest cercetator a vazut pui de urangutan in gradina zoologica, si a observat cat de diferit e de adult. Oamenii care descoperisera schelete de pui si de adult credeau ca sunt alte specii!!! Neotenia e considerata un factor implicat in umanizare. Omul e un primat neoten, de-aia are creierul mare, n-are blana etc.
Ceea ce ai citit tu se numeste biologia dezvoltarii, iar ideile extraordinare, pe care le-ai inteles, vin de la inceputul secolului XX, de prin 1922, inainte de Morgan si descoperirea mutatiilor. Teoria lui Darwin era in impas, desi nimeni nu se gandea ca nu e evolutie, dar mecanismele credeau ca sunt altele. Dupa descoperirea mutatiilor, variabilitatea, obiectul selectiei lui Darwin, avea suport fizic in mutatii. Asa ca a explodat sinteza moderna, noua teorie evolutionista, pe cand cercetarile de biologia dezvoltarii au fost uitate.
Daca vrei amanunte exista o carte romaneasca recenta, absolut originala, Civilizatia foametei/ o alta abordare a umanizarii", care e adepta biologiei dezvoltarii, mai mult explica de unde vine neotenia, la nivel biochimic, cu comparatie cu alte specii. Cartea, cum ii spune numele, e despre evolutie, umanizare si explica tot felul de caractere omenesti prin prisma biologiei dezvoltarii. Mai mult, arata ce factor de mediu a dus la umanizare. Cred ca te-ar interesa.

Neotenia a avut un rol major in aparitia omului, la fel poate si fuziunea cromozomiala, insa ramane de stabilit cum au evoluat lucrurile.

Fuziunea cromozomului 2, 2 ', de la antropoide si rearanjarea a alti cativa cromozomi !



48 – 46 cromozomi

It is assumed that in humans two chromosomes fused to produce a total of 46, because most gorillas also have 48.
When you take the two chromosomes that chimps and gorillas have, and put them end to end beside chromosome number 2 of humans, the banding pattern is almost identical. Click on this link to see a diagram of this: http://www.indiana.edu/~ensiweb/lessons/chr.bk1.html
What you are looking at is a diagram of chromosomes 1-4 with the human
chromosome on the left and the chimpanzee chromosome on the right.
Note that for chromosome 2, humans have one long one, but the chimp has two short ones there. This also shows only one of each chromosome for each species, so when you add the other set, that gives humans 46 and chimps 48.







Comparison of the Human and Great Ape Chromosomes as Evidence for Common Ancestry

When one looks at the chromosomes of humans and the living great apes (orangutan, gorilla, and chimpanzee), it is immediately apparent that there is a great deal of similarity between the number and overall appearance of the chromosomes across the four different species. Yes, there are differences (and I will be addressing these), but the overall similarity is striking. The four species have a similar number of chromosomes, with the apes all having 24 pairs, and humans having 23 pairs. References 1 and 2 each contain high resolution photomicrographs and diagrams showing the similarity of the chromosomes between the four species (ref. 1 only covers humans and chimpanzees, ref. 2 covers all 4 species). Furthermore, these diagrams show the similarity of the chromosomes in that every one of 1,000 nonheterochromatic G-bands has been accounted for in the four species. That means that each non-heterochromatic band has been located in each species. (I hope to add a scan of the full sets of chromosomes for all four species in the very near future. In the meantime I'll have to make do with a couple of examples of the most rearranged chromosomes that Don Lindsay has posted.)
Creationists will be quick to point out that despite the similarities, there are differences in the chromosomal banding patterns and the number of chromosomes. Furthermore, they will claim that the similarities are due to a common designer rather than common ancestry. Let's address the differences first, and then we will see if we can tease apart the conflicting scenarios of common ancestry vs. a common designer.
The following observations can be made about similarities and differences among the four species. Except for differences in non genetic heterochromatin, chromosomes 6, 13, 19, 21, 22, and X have identical banding patterns in all four species. Chromosomes 3, 11, 14, 15, 18, 20, and Y look the same in three of the four species (those three being gorilla, chimps, and humans), and chromosomes 1, 2p, 2q, 5, 7 - 10, 12, and 16 are alike in two species. Chromosomes 4 and 17 are different among all 4 species.
Most of the chromosomal differences among the four species involve inversions - localities on the chromosome that have been inverted, or swapped end for end. This is a relatively common occurrence among many species, and has been documented in humans (Ref. 8 ). An inversion usually does not reduce fertility, as in the case I have referenced. Don Lindsay provides a diagram of the chromosome 5 inversion between chimpanzees and humans scanned from ref. 1. Note how all of the bands between the two chromosomes will line up perfectly if you flip the middle piece of either of the two chromosomes between the p14.I and q14.I marks. The similarity of the marks will include a match for position, number, and intensity (depth of staining). Similar rearrangements to this can explain all of the approximately 1000 non-heterochromatic bands observed among each of the four species for these three properties (band position, number, and intensity).
Other types of rearrangements include a few translocations (parts swapped among the chromosomes), and the presence or absence of nucleolar organizers. All of these differences are described in ref. 2 and can be observed to be occurring in modern populations. The biggest single chromosomal rearrangement among the four species is the unique number of chromosomes (23 pairs) found in humans as opposed to the apes (24 pairs). Examining this difference will allow us to see some of the differences expected between common ancestry as opposed to a common designer and address the second creationist objection listed above. There are two potential naturalistic explanations for the difference in chromosome numbers - either a fusion of two separate chromosomes occurred in the human line, or a fission of a chromosome occurred among the apes. The evidence favors a fusion event in the human line. One could imagine that the fusion is only an apparent artifact of the work of a designer or the work of nature (due to common ancestry). The common ancestry scenario presents two predictions. Since the chromosomes were apparently joined end to end, and the ends of chromosomes (called the telomere ) have a distinctive structure from the rest of the chromosome, there may be evidence of this structure in the middle of human chromosome 2 where the fusion apparently occurred. Also, since both of the chromosomes that hypothetically were fused had a centromere (the distinctive central part of the chromosome), we should see some evidence of two centromeres.

Human Chromosome 2 and its analogs in the apes - from Yunis, J. J., Prakash, O., The origin of man: a chromosomal pictorial legacy. Science, Vol 215, 19 March 1982, pp. 1525 - 1530





Acest topic a fost editat de cyber-sapiens: 22 Jun 2008, 10:21 AM