[image caption and credit John Hawks: DH1 (left) and DH3 (center) of Homo naledi compared to KNM-ER 3733 from the Turkana Basin, usually attributed to Homo erectus. These skulls, shown to scale, illustrate the very small size of the Homo naledi cranium compared to African Homo erectus.]
From Hominins to Early Homo
Comment page for two readings about human origins, taking us from hominins to early Homo:
- Lavenda & Schultz chapter 5 (part 1 of 2), “What Can the Fossil Record Tell Us about Human Origins?” (119-132)
- “The Latest on Homo naledi” by John Hawks in American Scientist (2016).
for the Hartwick College Introduction to Anthropology 2016 course.
Rough notes below followed by Disqus comments.
Human Evolution: Mysteries, Debates
Why so much about teeth? In part, because teeth are what survive. However, sometimes much more difficult to deduce diet from teeth alone. See Dietary divergence of robust australopithecines for a great recent example.
Fossil record incomplete (does 5% even exist? 1%?)
Certain regions produce, others do not
Time gaps even in productive regions
Creatures don’t want to become fossils, and often eaten before they do
Almost no early chimp or gorilla fossils
Difficult to deduce “interbreeding species” from fossils
And–surprise!–genetic evidence has made things more complicated, not less
What we used to look for
Idea of intermediary creatures or “missing links”
Nice straight lines
Only fossil evidence
What we know now
Common ancestors, not missing links
Ancestor probably like, but not exactly the same as, chimp-bonobo
Feature separating last common ancestor of chimps-humans, 6-8mya = Bipedalism
Ape-like brain size, but becoming habitually bipedal
Diversity of bipedal species through most hominid-to-human history
Bushy models of “mosaic evolution” (Lavenda & Schultz:120)
Converging evidence from fossils, genetics, geology with computerized reconstructions
Used to think striding onto savanna
But probably more forested than previously thought (Lavenda & Schultz:122)
Seeing prey and predators; reaching into trees; thermoregulation; freed the hands; saved energy; cooperation
Endurance walking & possibly endurance hunting (Lavenda & Schultz:121)
None proved–could be combination or perhaps no single factor
Ardipithecus ramidus(Lavenda & Schultz:121)
Differently bipedal on ground, but grasping in trees?
Is Ardi really on what would become the main line, or another bushy branch?
Bipedalism also called walking
Endurance walking enables covering varied terrain (Lavenda & Schultz:121)
is a learned behavior
can vary by group (cultural styles) and among individuals
Learned behavior incorporated into biology?
[I’ve posted about this at Bipedalism is Also Called Walking.]
“Lucy” (Lavenda & Schultz:123)
Skeletal and other “hard” evidence of habitual bipedalism
(Lavenda & Schultz:125-126)
Or see The most complete Australopithecus skeleton in Lawnchair Anthropology (December 2017).
Early homo and stone tools
Co-evolving with durable tools since 2.5 mya (Lavenda & Schultz:131)
Importance of learned behavior
Culture vital to survival
New opportunities for niche construction
May have something to do with brain expansion? (Lavenda & Schultz:130)
And who was making those tools? See Kathryn Weedman Arthur’s work on Feminine Knowledge and Skill Reconsidered: Women and Flaked Stone Tools.
[I’ve posted about this at Stone Tools for 2+ Million Years.]
Where does Homo Naledi fit in?
“doesn’t fit in clearly yet” (Hawks, The Latest on Homo naledi)
“adapted like a human, without anything like a human brain” (Hawks)
Initially thought 2mya, although others now arguing 1mya: See Why don’t we know the age of the new ancient human? (noting the bizarre article title).
Long survival of other Homo lineages?
Perhaps yet another instance in which we get fooled by brain size
Stone tools, also known as culture, coincide with the origin of the genus Homo. Some experts believe that there are 12 species recognizable within the genus Homo, of which 11 are now extinct. I guess culture wasn’t such a great adaptation, after all.
–Jonathan Marks, “A first lecture on primate taxonomy”