Scientific Methods

Thursday, March 30, 2006

Wood & Collard's "Human Genus..."

Wood & Collard's "Human Genus..."


After reading the paper by Wood and Collard several times, I noticed that the paper does not mention Australopithecus afarensis (Lucy) except in review of two cladograms as opposing view points from other authors. I was rather concerned, since A. afarensis is probably one of the most important paleoanthopological finds in history, discovered in 1974 in the Northern Rift Valley in Ethiopia in the Hadar region.

It is suggested that A. afarensis may be the basis for human evolution, and that this species marked the transition from a completely acronomic life-style to bipedalism.

In one of my earlier comment entries on the blog site, I mentioned that in my opinion the removal of A. afarensis and A. garhi strengthened the hypothesis that Homo habilis and H. rudolfensis more strongly represent the Australopithecus genus, since there is a stronger definite character difference between both genuses without the confusion of the inclusion of A. afarensis and garhi, which both have a definite mix of features (mix of ape-like and human-like features)...I posed the question of exclusion to the senior author of the paper "The Human Genus" to which he responded the following:

"A. afarensis is masquerading under the binominal 'Praeanthropus africanus'." Binominal is the term in scientific language given for something that shares two names. "Praeanthropus afarensis is the result of a cladistic analysis carried out by Strait et al. (1977), which suggested that Australopithecus afarensis was the sister taxon Australopithecus africanus and other later hominins. The authors argued that the continuation of the use of the same genus name for A. afarensis and A. africanus, made it inevitable that the genus Australopithecus would be a paraphyletic taxon." (The term paraphyletic means very basically one clade minus another clade, for example, monophyletic groups are called clades, consisting of what is considered as being the only natural kind of group (a clade remember, is a theoretical family tree, representative of theoretical species only, and is not a true family tree of known individuals like your mother, father, aunt, sister etc.). Lets make a theoretical example to explain: If we took a non flying insect and a flying insect, which are both insects, and suggesting that they evolved along separate paths, if we take the non flying insects (in theory now, not true!) they would be a paraphyletic group, since an individual insect can't be defined as the non-flying insect and all its descendants, but rather as one clade minus another, or, the non flying insects minus the flying insects...this is confusing. [A search for the term "Paraphyletic taxon" is explained as: "a group of organisms in which the most recent common ancestor of all those organisms and some, but not all, of that ancestor's descendents are included. Paraphyletic taxa are recognized in Linnean and evolutionary systematics but not in cladistics

( http://www.palaeos.com/Systematics/Cladistics/paraphyletic.htm Accessed: 17/3/06 at 20:021).

Based on Strait et al. (1977), Wood explains that the suggested hypodigm [The definition of a hypodigm is all the material of a species available to a taxonomist] of A. afarensis be transferred to a different genus, that of Praeanthropus Senyurek, 1955, but, if Praeanthropus was used as the genus name, then the species name of afarensis no longer had priority, since Weinert's species name of Meganthropus africanus (yes, africanus), introduced in 1950, had priority over A. afarensis Johanson et al. 1978. This is rather confusing, however, the change in nomenclature (Name classification) would result in two hominin species called "africanus" (Australopithecus africanus Dart, 1925, and Praeanthropus africanus (Weinert, 1950), Senyurek, 1955).

Application was made to the International Commission of Zoological Nomenclature (ICZN) to have the specific name africanus Weinert, 1950 suppressed. The ICZN upheld the application in 1999. The ICZN also ruled that a news report in the "New Scientist" should have priority over Johanson et al., 1978. This ruling runs opposite to the guidelines set out in the ICZN handbook and Wood suggests that it be disregarded. Wood suggests therefore that if the A. afarensis hypodigm is removed from Autralopithecus then it should be referred to as Praeanthropus afarensis (Johanson et al., 1978), Strait et al. 1997.

In addition, Dr. Wood explained to me that the reason A. garhi was not mentioned in his paper was because it had not been discovered yet.

Dr. Wood suggests some reading for us class-mates, of the booklet:
"Human Evolution: A Very Short Introduction," with a description of the book available at http://www.oup.co.uk/isbn/0-19-280360-3.

I hope the above answers some questions. It certainly made me realise just how detailed the science can be. In addition, my initial assumptions based on my interpretation (and suspicion) of "The Human Genus," were incorrect.

Cheers
David Vaughan










David Vaughan
Senior aquarist, Quarantine
Two Oceans Aquarium
Cape Town, South Africa

dvaughan@aquarium.co.za
davidvaughan.b-logging.com
(021) 418 38 23

5 Comments:

  • Hi David
    Thanks for sharing that with us! Very interesting... Just don't know how your day somehow has more hours than mine?
    And as far as the names in italics etc. It came out perfect!

    By Anonymous Karen Marais, at Thursday, March 30, 2006 2:14:00 PM  

  • Magic and lots of coffee!

    How did you manage in the thick bush in the reserve today? I certainly had lots of fun!

    Cheers

    By Blogger davidvaughan, at Thursday, March 30, 2006 2:23:00 PM  

  • Dear DAVIDVAUGHN
    Bru you need to get out more, not everything i about insects and parasites!!

    By Anonymous Anonymous, at Thursday, March 30, 2006 3:43:00 PM  

  • Hello anonymous...

    Well, virtually every living thing is parasitised in one form or another, it could be argued that indeed everything is about parasites?

    Off to a movie...

    Cheers

    David

    By Blogger davidvaughan, at Thursday, March 30, 2006 8:52:00 PM  

  • Hi David,
    Yes I have to say I also do find the stuff you are posting interesting, thanx because I still have a lot to learn, especially about the parasites! See you! Elizabeth

    By Anonymous Elizabeth van der Merwe, at Friday, March 31, 2006 5:53:00 PM  

Post a Comment

<< Home