CH 6- THE FIRST HOMININS
What’s a Hominin?
• A phylogenetic species is one encompassing the smallest set of organisms that share a
common ancestor and that can be distinguished from other such set of organisms that
share a common ancestor and that can be distinguished from other such sets of
• Gibbons genus (Hylobatidae)& Humans (Hominindae)& Orangutans ( Pongo)
• Hominini: Tribe within the Homininae comprising humans (Homo), chimpanzees (pan) and
our most recent common ancestors.
Morphological Trends In Hominin Evolution
• Reviewing morphological trends in homini evolution is important for two reasons
1) Understand what features contributed to an adaptive radiation of hominins at a time
when contemporaneous fossil apes were disappearing,
2) Understand that there is no singular feature that resulted in the biological evolution of
human beings. Rather, modern humans are the result of millions of years if mosaic
Mosaic Evolution: this evolution is ongoing meaning that our species continue to be
subject to natural selection. We will change and eventually go instinct. The evolution at
different rates of various related or unrelated features or unrelated features within a
lineage or clade.
• Bipedalism: Habitual upright locomotion on two feet.
Dental & Cranial Morphologies
• Robust: physically strong, durable
• Gracile: slight, slender
• Increased Brain Size
Why Did Humans Evolve Bigger Brains?
1) Ecological- early hominins evolved larger brains to improve their ability to hunt or forage
for unpredictable food sources. A hominin would presumably need to improve its mental
map of a large area in order to assure access to food, particularly during periods of
2) Epiphenomenal- an increase in hominin body size resulted in a concomitant increase in
brain size. Epiphenomenal ( refers to a secondary by-product of some process)-ex pain is
an epiphenomenal result of damage to parts of our body)
3) Socialization-hominins evolved larger brains to deal with the increasing complexity of an
increased ability to network and scheme in large, complex societies.
• How to know its hominin bipedalism?
-adducted or valgus knee characterizes bipedal hominins? Adducted: Toward the midline
of the body. This means that the top of the femur is naturally farther away from the
middle of the femur.
• How Did Humans became bipedal?
- 1) Feeding Postures: this hypothesis holds that early hominins were pre-adapted to an
upright posture due to their evolving from an ape-like primate that maintained an
upright body posture in the trees. As early hominins transitioned from an arboreal to a
more terrestrial lifestyle thy maintained their upright feeding patterns, which led
eventually to habitual bipedalism. - 2) Behavior- this hypothesis holds that bipedalism evolved to improve the ability of
males to carry food resources to their mates and offspring. In this theory male
provisioning was a necessary outcome of the monogamous, bipedal hominins enjoyed
increase fitness because they could invest more care and protection into a few
offspring. This theory implies a sexual division of roles in infant caregiving, with a
female looking after the immediate physical needs of the offspring and a male
undertaking much of the foraging needed to feed the female, offspring and himself.
- 3) Thermoregulation: this theory holds that bipedalism evolved to improve the heat-
dissipating abilities of early hominins. The earliest hominins evolved in equatorial
Africa, which has intense solar radiation and heat, particularly in open environments. A
vertical body pos