Hunting the First Hominid
What to Look For?
What happened, exactly, and to whom,
remain to be discovered. Two newly discovered fossil species
have each been proposed to be the First Hominid. This circumstance
raises a significant issue: How would we know the First Hominid if
we saw it?
Making a list of key features that differentiate apes from people is
not difficult, but misleading. It is absurd to expect that all of
these differences arose simultaneously during a single evolutionary
event represented by the final fork on the hairy Y diagram. The
first ape on the gorilla-chimp lineage was neither a gorilla nor a
chimpanzee, for modern gorillas and chimps have had at least 5
million years to evolve in isolation before arriving at their modern
form. In the same way, the First Hominid on our lineage was not a
human and did not possess all of the characteristics of modern
Using a hairy Y diagram, we can limit the number of contenders for
the essential or basal hominid adaptation:
—Hominids might be essentially bipeds. All known
hominids are bipedal; no apes are.
—Wishful thinking aside, hominids are not simply brainy apes.
Alas, until about 2 million years ago no hominid had a brain larger
than an ape's relative to its body size.
—Hominids might be apelike creatures that have lost their
sexual dimorphism. Sexual dimorphism is exhibited as male-female
differences that are not related to reproduction. For example, male
orangs are typically much larger than females and have longer canine
teeth that hone sharper with wear. The fossil record shows that
hominids lost their dental sexual dimorphism first, since all known
hominids have small and flat-wearing canines. In contrast, sexual
dimorphism in body size persisted in hominids until about 2 million
years ago, when the genus Homo first appeared.
—Thick dental enamel may be a key hominid trait. All hominids
have thick enamel, whereas all fossil and living apes (except those
in the orang-utan lineage) have thin enamel. Because the fossil
record of apes is so poor, we do not know whether the primitive
condition for apes and hominids was thick or thin enamel. Indeed,
how enamel thickness is to be measured and evaluated has generated
many pages of debate.
—Hominids are hand-graspers or manipulators (from the Latin
for hand, manus), whereas apes are foot-graspers. These
differences are reflected in the sharp contrasts in the hand and
foot anatomy of apes and humans. Apes have divergent big toes and
long, curved toe bones for holding onto branches; their thumbs are
short and cannot be opposed to the other fingers for skillful
manipulation. Human beings are the opposite, with long, opposable
thumbs and big toes that are closely aligned with the remaining
short, straight toes. Human feet are nearly useless for grasping but
are well adapted to bipedalism. An intermediate condition occurs in
early hominids such as Lucy (the best-known individual of
Australopithecus afarensis), who had opposable thumbs
and numerous adaptations to bipedalism, and yet retained rather long
and curved toes. Lucy and probably other types of
Australopithecus were walkers, hand-graspers and
somewhat compromised foot-graspers.
A description of our desired prey, then, might read like this:
An ape-brained and small-canined creature, with dental
enamel of unknown thickness. Large if male but smaller if female.
May be spotted climbing adeptly in trees or walking bipedally on the
ground. Last seen in Africa between 5 million and 7 million years
From this description, can we identify the First Hominid? Well,
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