New species designation in doubt
A species is the fundamental taxonomic category we use in biology and it’s a very difficult judgement to make, especially in the fossil record where you’re invariably looking at only a small portion of the animal, in this case it’s a few teeth and jaws.

You’re making the judgement as to whether or not this constitutes a new lineage that lies outside the variation that you’d expect.

And some of us recognize much higher ranges of variation than others.

Here you’re comparing things like molar and enamel thickness and size, and various characteristics of the dentition, and having to make the judgement as to whether these are significantly different than anything we’ve seen in Lucy’s species to justify a new lineage.

Many of us feel that, in this case, it’s probably not justified.  That includes Lucy co-discoverer Tim White at Berkeley, one of Haile-Selassie’s mentors, and William Kimble, director of the Institute of Human Origins at Arizona State University. 

Sharing habitats with Lucy 
Lovejoy says part of his skepticism stems from the behavioral implications of adding a new species side-by-side with Lucy.

If in fact Haile-Selassie’s specimens do represent a new lineage, then it means there were two contemporary lineages that must have had at least something called character divergence, which means they were occupying different niches within the environment.  That would be one of the implications.

When we look at hominids in this particular time range however, they all seem to share the same set of very clear, unmistakable specializations -  upright walking; small canines, which has social implications – so undoubtedly even if Yohannes’ specimens are a separate species, they still had the same social structure as did Lucy’s species.

So it’s a matter of scientific debate.

Theories vs facts in human origins debate
AS Darwin pointed out,  shooting down someone’s theory is a positive thing, as long as you get the facts right.

In this case the facts are still in dispute - that these teeth represent a new species.

Some scientists say they’re within the variation seen within Lucy’s species Australopithecus afarensis, but Haile-Selassie says they’re not.

And we won’t be able to answer the question fully until more specimens are found that can be satisfactorily added to the proposed new species, Australopithecus deyiremeda.

Haile-Selassie needs to build up the hypodigm, the individuals that we define as members of the new species.

But whenever new fossils are found, no matter how much we disagree about it, it always adds to our understanding of human evolution.