The macroevolution of our ancient lineage: what we know (or think we know) about early hominin diversity, Ackermann & Smith, 2007

Ackermann and Smith highlight issues within paleoanthropology related to hominin diversity, such as the lack of information related to interspecific and intraspecific variation of the hominins. They comment frequently about the problematic use of the word 'mosaic' to describe morphological traits.
Specific important questions brought up in the article:

What constitutes the primitive condition?

• Is thick or thin enamel primitive? Does it matter/is this a meaningful question given the information we have? 
• Reduced canines = similar argument

Why have questions of variation been avoided despite hominins being so speciose?

• Small sample size
• Mosaic, resulting in adaptive radiations

Early hominin environment

• broad differences in environment don't provide a lot of information toward the adaptive underpinnings of hominin diversity
• ex: Papio hamadryas  lives in many diverse habitats (only a single species)
• Paranthropus = best info for analyzing adaptive change
• Large teeth suggest diet change, what type of change? People intitially though hard-objects, but isotopes reveal grass? Was it fallback foods that promoted evolutionary change and the need to access a WIDER range of resources (due to seasonality) that promoted phenotypic change? 

Mosaic morphology

• Primates, specifically new world primate share an overall pattern of trait integration and covariation
• vast bulk of cranial diversification is related to size
• Hominins seems to be having very different adaptation patterns, so what is going on? not related to size but shape

Most probably explanation for diversification is that they were occupying distinct niches driven by resource exploitation