How are the East African gracile australopiths different from each other:How might the Variability Selection Hypothesis be tested against new fossil finds, and what is the potential role of climate in this process

How are the East African gracile australopiths different from each other

With increased emphasis on fieldwork and survey in paleoanthropology, we have seen a significant increase in fossil finds over the last several decades, including a new species not discussed in lecture (but included in your textbook, Ch. 10:303-304). These discoveries were made at the sites of Burtele and Wayteleyta in Woranso-Mille (central Afar region), Ethiopia and include a 3.4 Ma partial foot and 3.3 – 3.5 Ma craniodental remains of a new species of australopith, Australopithecus deyiremeda. These remains are from deposits that are slightly earlier that those associated with Australopithecus afarensis.

Here are two blogs about these recent discoveries:

Australopithecus deyiremeda: New human ancestor in Ethiopia (Links to an external site.)Links to an external site.. Science 2.0

Burtele hominin – New kid on the evolution block (Links to an external site.)Links to an external site.. Science 2.0

Here is a ‘News & Views’ summary of the new finds published in Nature in the same issue that published the peer-reviewed paper announcing the new species:

Spoor, F. (2015) Palaeoanthropology: The middle Pliocene gets crowded (Links to an external site.)Links to an external site.. Nature 521:432-433.

Here are the original peer-reviewed papers, if interested:

Haile-Selassie, J. et al. (2012) A new hominin foot from Ethiopia shows multiple Pliocene bipedal adaptations (Links to an external site.)Links to an external site.. Nature 483:565-569.

Haile-Selassie, J. et al. (2015) New species from Ethiopia further expands Middle Pliocene hominin diversity (Links to an external site.)Links to an external site.. Nature 483:565-569.

As you explore the required websites for this (and later modules), the Smithsonian’s website ‘What does it mean to be human?’ includes a number of excellent reviews on current topics in the field. One page entitled ‘Climate Effects on Human Evolution (Links to an external site.)Links to an external site.’ highlights the work of Rick Potts, who argues for environmental instability as a catalyst for hominin evolution. The first half of this page focuses on his ‘Variability Selection Hypothesis’ and his arguments for the evolution of the genus Homo. Similar arguments can be made for the increased diversity of fossil hominins in the Pliocene epoch (5.3 – 2.6 Ma) as exemplified by myriad australopith species that have been recovered in deposits associated with the East African Rift Valley (e.g., Kenyanthropus not included in your text, and the new species Australopithecus deyiremeda discussed above).

For this week’s discussion, consider the merit of the Variability Selection Hypothesis as a means to evaluate the diverse Pliocene hominin fossil record of East Africa. As indicated on the Oxygen isotope curve figure on this webpage, there is an arrow with the text ‘Increased climatic fluctuation, environmental uncertainty’ at this point in time that coincides with the dates for these new fossil discoveries.

How are the East African gracile australopiths different from each other? How might the Variability Selection Hypothesis be tested against new fossil finds, and what is the potential role of climate in this process (hint ‘directional selection’ Ch. 4:105-107)?

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