In 2004, paleontologist Neil Shubin made the discovery of a lifetime: A fossil, later named Tiktaalik, that appeared to bridge the gap between ocean dwelling fish and land walking amphibians. As explained in NOVA: Your Inner Fish, the discovery of Tiktaalik reveals evidence of the shared ancestry of humans with ancient fish.
NOVA: Your Inner Monkey extends Dr. Shubin’s inquiry into the origins of the human body. The 1870 discovery of Notharctus, a 50-million-year old North American primate ancestor, revealed one of the earliest animals to have fingernails like our own. This creature also possessed a hand and divergent thumb, ideal for life among the trees. Primates also feature excellent color vision, which is likely the gift of a mutation that duplicated an opsin gene regulating vision. Color blindness in humans harkens back to a time when our distant primate ancestors lacked the rich color vision that we now possess. This new ability apparently came at a price, the degradation of our sense of smell. Today’s dogs possess a sense of smell thousands of times more sensitive to humans, and we humans rely more upon our sense of sight. Much of the mammalian capability to smell has become dormant, with these genes becoming inoperative but still present in the human genome.
That most human of abilities, that of bipedalism, or walking on two legs, can be traced back to Ethiopian fossils dating 4.4 and 3.2 million years ago. Lucy, the famous fossil of Australopithecus afarensis, is described by her discoverer, Neil Shubin’s childhood hero Donald Johansen. The evidence that Lucy walked on two legs comes from the examination of her inward directed leg bones and human-like pelvis. An earlier human ancestor, Ardipithecus or Ardi, dates back to 4.4 million years. Ardi was likely bipedal, but also spent time in the trees due to evidence of feet still possessing grasping toes. Ardi’s pelvis displays a mosaic of human and ape features, and she is a representative of an important milestone in human history; the descent from the trees towards bipedalism. Walking on two legs likely led to the advancement of our species, it freed the hands for tool building and manipulation of the environment. Despite this, the “engineering nightmare” of our once horizontal back becoming upright has resulted in the preponderance of back problems we face. 80% of Americans will report back problems at some time during their lives. The human predisposition to back problems is illustrated by a visit to the Hamman-Todd collection of 3000 human skeletons at the Cleveland Museum of Natural History.
The development of the human brain is illustrated by a visit to an African site littered with 2-million-year-old stone tools, the work of Homo habilis (Handy Man). Next, the abilities of monkeys and human infants of the same age are compared, in particular an experiment involving object permanence, the knowledge that once visible hidden objects still exist, which is readily displayed in a 3-month old monkey, but not in a human infant of the same age. This leads to a discussion of the advantages of the long developmental period of human infants whereby cognitive abilities are allowed to become manifest over an extended period of nurture and learning.
The video now takes us back much further with the dissection of a shark and a human brain. Each brain, though vastly different in many respects, displays the same three-part geometry of forebrain, midbrain, and hindbrain. Even further back along the evolutionary tree of life, we see Amphioxis, a primitive creature related to some of the earliest known pre-verterbrate ancestors dating back over 500 million years. Amphioxis is a rod shape pre-vertebrate found in ocean sands. It exhibits a stiff rod along its body, a prototype of the vertebrate spine, and an elongated nerve running its body length terminating in a small protuberance at the front end of the animal, a sort of proto-brain. The DNA of Amphioxis possesses genes similar to those in humans that form a “zip code” for brain development, telling which areas to grow and where. This indicates that the genes responsible for human brain development can likely be traced back to pre-vertebrate ancestors that lived 500 million years ago!
Your Inner Fish is a magnificent documentary series that demonstrates how the human body is related to several ancestral creatures such as ancient fish, reptiles, and primates. We are able to see vestiges of these past forms in our own bodies today, and we can experience a sense of awe and wonder at the depth of time represented in earth’s history, and of our kinship with all other life on earth. Viewing humanity in an evolutionary sense heightens our appreciation of all of earth’s diverse life, and calls on us to be better stewards and caretakers of this planet.
The zip file download contains a two-sided video worksheet consisting of 48 multiple choice and true-or-false questions, along with an answer key, and files in both MS Word and PDF formats. You will need to obtain a DVD of the video, use the PBS Internet site, or YouTube.
The entire video series, Your Inner Fish, Your Inner Reptile, and Your Inner Monkey is available on the Howard Hughes Medical Institute (HHMI) Biointeractive Internet site.
Neil Shubin's wonderful book Your Inner Fish was the inspiration for this video series.
Note: The video contains brain dissection scenes.