December 30, 2010

Cranial vault shape in fossil hominids

Homo sapiens is sometimes said to be derived from Homo heidelbergensis a species whose holotype is the Mauer mandible and which is sometimes extended to include the Broken Hill skull (Kabwe, Homo rhodesiensis) from Africa. This study seems to conflict with the earlier one which supported the grouping of H. heidelbergensis as an Afro-European taxon. Tim White suggested that Kabwe is ancestral to H. sapiens idaltu (Herto) which is ancestral to us. However, the Omo 1 skull is more ancient than idaltu and also more modern anatomically.

To say that the palaeoanthropological record is a mess would not be far from the truth...

Homo. 2010 Oct;61(5):287-313.

Cranial vault shape in fossil hominids: Fourier descriptors in norma lateralis.

Lestrel PE, Ohtsuki F, Wolfe CA.

Abstract
Two major views of human evolution have elicited considerable controversy. These are: [1] the "out of Africa" hypothesis and [2] the "multiregional" hypothesis. This paper is an attempt to try to reconcile these two scenarios using hominid cranial vault data. Elliptical Fourier functions (EFFs) were used to describe, in visual and numerical terms, the shape of the human cranial vault in norma lateralis. Using jpeg images, contours of the cranial vault of a large sample of hominid specimens were pre-processed in Photoshop CS and rotated in 2D space (positional-orientation) so that a line drawn from nasion to porion was horizontal. The cranial vault image was then digitized with 72 closely-spaced points and submitted to a specially written routine that computed EFFs normalized by scaling (size-standardization). This ensured that the representation was invariant with respect to starting point, size and orientation. Statistically significant differences were found between the H. sapiens sample and both the H. erectus and H. neanderthalensis samples. In contrast, there were no statistically significant differences between the H. erectus and H. neanderthalensis groups, leading to three conclusions: [1] the similarity in cranial vault shape between H. erectus and H. neanderthalensis suggests a single gradually evolving lineage; [2] The taxon H. heidelbergensis can be embedded into the H. erectus→H. neanderthalensis line; and [3] H. sapiens seems to be a separate evolutionary development and is considered here either as a separate species or as a possible example of an allopatric semispecies (Grant, 1977). The results here suggest that human evolution over the last 2 Ma may turn out to be neither totally multiregional or simply out of Africa but rather represents a considerably more complicated picture.

Link

3 comments:

terryt said...

"The results here suggest that human evolution over the last 2 Ma may turn out to be neither totally multiregional or simply out of Africa but rather represents a considerably more complicated picture".

I think that is the conclusion you've been coming to lately, isn't it? I've certainly considered it to be the case for many years. Haplogroup evidence is not the complete story.

eurologist said...

I have a number of problems with this paper, and I think it highly overreaches its results. They claim that heidelbergensis is basically indistinguishable from erectus and neanderthalensis, and thus should be dismissed as a transitional form. However,

* Just being transitional doesn't mean a grouping is not important (all groups are transitional);
* since they don't evaluate volume, they neglect the main characteristic that changed from erectus towards the end of heidelbergensis: namely, the achievement of sapiens-like brain size;
* just because the characteristic they chose is not suitable to distinguish well, this does not mean species (or groupings) are not well-distinguished: see the latest Mauer mandible analysis that finds clear distinction of heidelbergensis based on the mandible, alone.

We know sapiens did not evolve from neanderthalensis, but it might very well have evolved from heidelbergensis sensu lato, perhaps even twice or three times (including recent admixture). Yet more reason to keep that definition as an important grouping (I think the species terminology is simply useless in this context and just amounts to semantics).

terryt said...

"Yet more reason to keep that definition as an important grouping (I think the species terminology is simply useless in this context and just amounts to semantics)".

You may be interested in reading my take on the situation from some time ago:

http://humanevolutionontrial.blogspot.com/2009/06/human-evolution-on-trial-species-or-not.html