sábado, marzo 22, 2008

Whereupon Lewontin is criticized, and "Phyloepigenetics" is born

In "The triple helix" Lewontin seems to contradict himself a bit on the importance of genes. Consider this paragraph:

"Of course it is true that lions look different from lambs and chimps and humans because they have different genes, and a satisfactory explanation for the differences between lions, lambs, chimps and us need not involve other causal factors"
(Italics are mine)

Since Lewontin in his next breath talks quite a bit about the importance of environment and random noise in development, we are forced to wonder why they would not count as causal factors when it comes to explaining inter-species differences.

I suspect this is the result of a typically neodarwinian mistake born from the circular logic of their definition of evolution. Because "evolution is genetic change of populations", when observing a difference that is species-level (evolutionary) they get confused and think they can assume that difference to be the result of natural selection for genetic mutations (unless it is a very obviously a non-adaptive difference, in which case it is still genetic mutations, and drift rather than selection) . This argument in fact is repeatedly encountered in the discussion over whether human "intelligence genes" exist or not. "Evolutionary" psychologists (ultradarwinians) argue that the fact the human brain has evolved from smaller, less-smart brains like those of other apes implies natural selection for "intelligence genes" must have occurred in the human line, and thus that genes capable of increasing fitness through intelligence must indeed exist (The fact being that their effects are difficult to detect. Only using lots of data, statistical correlations for only very small increases in IQ scores is all that is ever detected for an alleged "intelligence gene)"

This argument, that seems so impeccable to those accustomed to thinking with a neodarwinian cap, can be exposed for the misleading definition-game it is when we stop to analize a few case-studies. The human trait of bipedism for instance. Below is the photograph of one of two "wolf girls", Amala and kamala, that were raised by wolves in India and then "rescued" into civilization in the 1920's. Extensive written and photographic documentation were produced by the priest who took care of them. As you can see in the photograph, the girls used quadrupedal, rather than bipedal, locomotion. The priest tried hard but made little progress training them into walking like people. They did not speak and and had obviously subnormal cognitive capacities for human standards .

You would think that genetic influences over general human anatomical structure would be sufficient to lead to bipedality. However, let us remember that in our ontogeny we do, in fact, learn to walk bipedally. This important difference between humans and other animals seems to not come about without an appropiate context, provided by interactions among humans, which are in fact required for preserving the behavior of bipedal walking .

Let's talk about symbolic language, another difference between humans and other species. Beyond Amala and Kamala, it is clear from numerous documented cases of feral or cruel upbringing of children, that children deprived from human interaction will not learn to speak and will develop a severely subnormal intelligence. But perhaps more interesting is the reverse experiment, that is, not only is it possible that a human may not learn to speak despite of any "language genes", but also, it is a fact that non-human primates can learn sign language and use it to communicate, despite any lack of "language genes". In this case, an important part of that species difference has been phenocopied in the other species, once again, with the aid of an adequate environmental context.

So, there definitely is an epigenetic component to the explanation of cross-species differences. A purely genetic causation could never be a satisfactory explanation. We will find that, as we compare the terminal taxa of a phylogentic tree, we will be able to see nodes in which clearly different epigenetic conditions have become established and can be directly responsible for great phenotypic differences or epigenetic apomorphies ; the sublime confirmation of everything is, of course, the experimental phenocopy or reversal through alteration of the suspect epigenetic factor.

I can think of several confirmed examples from non-human organisms and simple phenotypic traits, as well as several epigenetic hypotheses that have never been discussed before as explanations of differences between species, perhaps for lack of a more formal approach. I thus propose we begin by calling this approach Phyloepigenetics.

The intention of this post is to start several posts where we will be studying and discussing probable cases of epigenetic differences at the species-level, and thus make ourselves with a litte more "cultural baggage" to defend this new approach. I invite everyone to share examples!! I will soon be posting one about ...dinosaurs! Phyloepigenetics can be paleo, too.

Lewontin, R. 2000 The triple Helix: Gene, Organism and Environment. Harvard University Press.

17 comentarios:

RSuárez dijo...

Excelente iniciativa. Así, además de darle robustés empírica al modelo, mostramos su poder explicativo... y predictivo!! (justamente lo que más alegan quienes no entienden la autopoiesis).

Anónimo dijo...

aí segue um link de um site de biblioteca online na área de biologia. São mais de 3000 títulos da área, muitos deles antiguíssimos.

aí nesse endereço eu consegui o pdf do livro "Regeneration" de TH Morgan (1901)

Ps.: Chico, aí também tem aquele livro do Hertwig: "The biological problem of today: epigenesis or preformation?"



Anónimo dijo...

aliás, esse livro do Hertwig sobre "the biological problem of today", é de 1900!!!

Sanders dijo...

harto de bateson, de driesch, de roux...excelente sitio

RSuárez dijo...

chucha el link bueno!! puros clásicos para el deleite de la historia de la biologia!!!
Está la obra de Erasmus Darwin, el abuelo, quién era medio genio, fundó su "nucleo decenio" llamado sociedad lunar de divagaciones científicas y con su idea de "zoonomía" anticipaba a lamarck en la idea de evolución por herencia de modos de vida... ja!

... de wikipedia:
"Would it be too bold to imagine that, in the great length of time since the earth began to exist, perhaps millions of ages before the commencement of the history of mankind ... all warm-blooded animals have arisen from one living filament, which the great First Cause endued with animality, with the power of acquiring new parts, attended with new propensities, directed by irritations, sensations, volitions and associations, and thus possessing the faculty of continuing to improve by its own inherent activity, and of delivering down these improvements by generation to its posterity, world without end!"

Sanders dijo...


Cristian dijo...

guena Gustavo! Super buen dato!!!

Ta guena la reflexion de la evolucion del lenguaje..

Interesante, por que desde el punto d vista del desarrollo del comportamiento es el extremo de la contextodependencia...

Chico dijo...

Porra!! E tem Cope, Hyatt e vários outros que construiram o "eclipse do darwinismo" no fim do século XIX! Que achado, tu devias tá desesperado por este livro do Morgan!

Eu conhecia este sítio: http://www.archive.org/index.php
Tem algumas coisas interessantes também, mas este tá muito melhor.

Chico dijo...

A última edição do Philosophical Transactions of the Royal Society B: Biological Sciences (363, Number 1497 / May 12, 2008) está intitulada ‘Integration of ecology and endocrinology in avian reproduction: a new synthesis’. Quem sabe revirando lá haja um bom caso de Phyloepigenetics (provavelmente não apreciado pelos autores). Acho que vale a pena dar uma olhada.

Sanders dijo...

excelent, Chico
The case of Amala and amala could be questioned because it could be a case of combined congenital bad equilibrium and retardation, as reported in quadrupedal families in Turkey ad Chile. However the facial morphology of Amala and Kamala are conspicuosly "normal" in comparison to these. If we are to believe the priest, they exhibited several behavioral traits of wolves, such as howling.
There are some pictures of Amala standing up, one of the few achievements of the priest, which I'm not sure is possible with congenital bad equilibrium. In fact the priest got her to walk bipedally, but she frequently reverted to quadrupedal.

Anónimo dijo...

consegui esse link via Kay Saalfeld!


Anónimo dijo...

hola decenios

encontre este paper bien pulento de exaptacion en el origen de los cachos en escarbajos machos del genero Onthophagus. algunas especies de este genero tienen prominentes cachos en la cabeza que ocupan para pelear con otros machos. en ojos de los seleccionistas un clasico ejemplo de seleccion sexual...... hasta ahora. estos autores estudiaron el desarrollo de varias especies del genero, incluidas especies que no tienen cacho y ademas chantaron sus resultados sobre una filogenia. como siempre el estudio comparativo revelo la verdad oculta. resulta que todas las especies del genero presentan un evaginacion en la cabeza, un proto cacho, durante la etapa de larva. este cumple como funcion romper la cuticula en la transicion larva-pupa y es reabsorbida durante la ultima etapa pupal. la filogenia indica que este caracter es ancestral en el genero. osea , el origen de este rasgo es un simple cambio en el desarrollo, solo hace falta que no se reabsorba la estructura larval durante la pupacion.
otros datos interesantes es que en especies sin cachos, no es extrano encontrar individuos con proto-cachos, probablemente como resultado de la no reabsorcion de los cachos larvales. si a esto le sumamos que los machos de todas las especies, cachos o no, pelean por la hembras, pareciera que el echo de que tengan cachos es una mera casualidad, un error en el desarrollo que queda co-optado en el modo de vida, solo por que este lo permite, y que el origen del rasgo no tiene nada que ver con las peleas. (si fuera asi todas las especies tendrían cacho dado que todas pelean).

espero les guste el ejemplo, si es que no lo conocían de antes.



Sanders dijo...

está buenísimo el caso. hace mucho que los darwnistas no pueden explicar porque la seleccción sexual no continúa exagerando y exagerado los rasgos sexis. Y es que no, no son cambios gradualmente acumulados.El caso del cacho de escarabajos ejemplifica bastante claro lo fácil que es tener un "monstruo" para un rasgo "sexualmente seleccionado"

Cristian, si quieres escribir un pst, pos ya sabes! espero que ya tengas la clave...

Anónimo dijo...

I wish not agree on it. I think warm-hearted post. Particularly the designation attracted me to be familiar with the unscathed story.

Anónimo dijo...

Genial fill someone in on and this enter helped me alot in my college assignement. Say thank you you on your information.

Anónimo dijo...

The story of Amala and Kamala is a fake, as you can easily check on google. See Serge Aroles, L'Énigme des enfants-loups. Une certitude biologique mais un déni des archives (1304-1954), 306p, ed. Publibook, nov. 2007, (ISBN 978-2-7483-3909-3). Cheers.

Anónimo dijo...

The story of Amala and Kamala is a fake, as you can easily check on google. See Serge Aroles, L'Énigme des enfants-loups. Une certitude biologique mais un déni des archives (1304-1954), 306p, ed. Publibook, nov. 2007, (ISBN 978-2-7483-3909-3). Cheers.