Aseel’s Reviews > Your Inner Fish: a Journey into the 3.5-Billion-Year History of the Human Body > Status Update

Open and close your mouth:
your teeth always come together in the same position, with
upper and lower teeth fitting together precisely. Because
the upper and lower cusps, basins, and ridges match closely,
we are able to break up food with maximal efficiency. In
fact, a mismatch between upper and lower teeth can shatter
our teeth, and enrich our dentists.

Reptiles also lack the precise occlusion—the
fit between upper and lower teeth—that humans and other
mammals have. Also, whereas we mammals replace our
teeth only once, reptiles typically receive visits from the
tooth fairy for their entire lives, replacing their teeth
continually as they wear and break down.

Our limbs exist in three dimensions: they have a top and a
bottom, a pinky side and a thumb side, a base and a tip. The
bones at the tips, in our fingers, are different from the
bones at the shoulder. Likewise, our hands are different
from one side to the other. Our pinkies are shaped
differently from our thumbs.

But there is a big limitation to working with
fossils. We cannot do experiments on long-dead animals.
Experiments are great because we can actually manipulate
something to see the results. For this reason, my laboratory
is split directly in two: half is devoted to fossils, the other
half to embryos and DNA. Life in my lab can be
schizophrenic.

From common parts came a very unique
construction. We are not separate from the rest of the living
world; we are part of it down to our bones and, as we will
see shortly, even our genes.

Do the facts of our ancient history mean that humans are
not special or unique among living creatures? Of course not.
In fact, knowing something about the deep origins of
humanity only adds to the remarkable fact of our existence:
all of our extraordinary capabilities arose from basic
components that evolved in ancient fish and other
creatures.

The important, and
often surprising, fact is that most of the major bones
humans use to walk, throw, or grasp first appear in animals
tens to hundreds of millions of years before.

the
earliest creature to have the bones of our upper arm, our
forearm, even our wrist and palm, also had scales and fin
webbing. That creature was a fish.

The bones of the front fin of Tiktaalik— a fish with a
wrist.

Our upper arm
has a single bone, and that single bone, the humerus,
attaches to our shoulder. In the lungfish, we have a fish with
a humerus. And, curiously, it is not just any fish; it is a fish
that also has lungs. Coincidence?