ADM presents a set of observations showing that a phenotypical character evolved following a particular direction, and done show in a discontinuous manner, with several steps becoming shorter over time. And as reversion isn’t observed, she conclude to irreversibility of the process.
Those are well documented facts, and I trust ADM as paleontologist. I regret that people talked about falcification, probably without taking enough time to think about such a severe accusation.
The central point, which wasn’t considered as far as I know about this case, is that ADM presented data about a phenotypical variation, and that’s all. No genetic data. Of course fossils can’t provide this information, and this is maybe the reason why she didn’t considered the genetic aspect of the problem. But she make an interest parallel with embryogenesis, and this is probably the source of genetic data one would like to consider, as embryos are available from several species of primates, including humans.
I will present, and try do do it in the simplest manner, a quite simple model presenting all the characteristics that leaded ADM, and other, to consider that these observations where incompatible with darwinism. This isn’t the model I would start with to explain ADM findings; a more elaborated one must be constructed, taking in account all information available about the development of the skull, including genes’ expression variations which determine at the molecular level the steps of the process.
What is the interest of the model I’m presenting? Showcase that random alterations at the genome’s level, associated with natural selection factors (at least one) may lead to the directional, discontinuous evolution of a phenotypical trait.
I kept the model as simple as possible: one gene, one selection factor; thus it will be accessible to everybody with a basic knowledge of biology. I present it in three steps:
One to showcase directional evolution of a phenotypic trait, and it’s reversibility if external conditions change, due to randomly occurring mutations.
One to show how phenotypic jumps may be observed, corresponding to particular, randomly occurring, genetic events.
One to make evident that the succession of such phenotypical jumps may be accelerated while mutations are kept random.