Sunday, April 4, 2010

The Human Missing Link

Scientists hoping to provide more evidence of evolution often attempt to locate fossils that are the most recent common ancestors of two species that are extant today. This common ancestor is called the missing link. On page 194, Jerry Coyne states that even Darwin “remained unconvinced that natural selection could explain the higher mental faculties of humans.” Thus, we needed to find fossils in human ancestry that could show our own evolution. What were these fossils, and how did it help us show that our mental faculties did indeed develop by natural selection? Also, the exact missing link that would provide us our most recent common ancestor with chimpanzees and bonobos has never been found. What would such a link look like, and what kind of effect might it have on the scientific community and the public at large if it was found?


  1. The first question posed in this prompt is easy enough to answer, as specific examples are provided in the text. Those examples include the bones of Neanderthals found in 1871, the first Homo erectus bones found by Eugene Dubois that included “a skullcap, some teeth, and a thighbone” (Coyne 194), the Taungs child found in 1924, the find of “Lucy” in 1974 by Donald Johanson, and, as Coyne puts it, “a host of other finds” (Coyne 194). Also, DNA evidence from many apes allowed us to further demonstrate our close relationship with other apes. It turns out that there are “lesser apes” and “greater apes” (Coyne 195), and we are part of the greater apes. All of the apes, be it lesser or greater, have similar traits, yet the greater apes show higher intelligence. This is further demonstrated in a Richard Dawkins presentation, when he states that “we are all cousins, we are not descended from chimpanzees” (Dawkins) yet we have a common ancestor that split off into two different species at one point, creating chimps and humans. The cool thing is that chimps have the highest intelligence (besides humans) of all the greater apes, which means that that intelligence is somehow linked to evolutionary passing of traits into the two species, human and chimp. This point is backed up in a Talk.Origins article, stating that “the intellect is not unique to the human, it is quite well developed in a number of the other higher animals” (Talk.Origins). However, this also begs the question of what this transitional species would look like, as it is well known that the fossil of one has not been discovered yet.

    Since no concrete evidence exists yet of such a transitional species because of early humans only living in “Africa under dry conditions not conducive to fossilization” (Coyne 195), the only sort of attempt we can make at determining what the looks of the transitional species would be is our best educated guess. Like with the Tiktaalik roseae discovered by Neil Shubin (Coyne 37), the best way of determining looks is by deducing what traits would be shared by both species and going on a basis of comparison between those traits and different ones. Those traits in humans and chimps would be forward-facing eyes, thirty-two teeth, a hinged jaw, and a thick cranium. Then, we take an “average” of the looks of both species, but in this case, the ancestor would probably look more ape than human in features because all apes look similar and humans are the “odd ones out” (Coyne 195). A common ancestor would definitely display those shared traits like the teeth, and look like a morphed human-chimp conglomeration otherwise. Deductive reasoning is all we have to go on now, and until that very fossil is discovered providing the “missing link” between humans and chimps, that’s our best shot at this particular issue.

    Page 194 of the book
    Page 195 of the book
    Page 37 of the book

  2. Over the past century and a half, scientists have found human like fossils which help explain how Homo sapiens evolved and possessed higher mental faculties as compared to other species. In 1891 Eugene Dubois discovered bones of a species with a rounder and smaller skull than humans which is now known to be fossils of Homo erectus. Also, in 1974, the bones of "Lucy" proved the existence of a bipedal humanoid living approximately 3.2 million years ago. Most recently, discovered in 1992, "Ardi" closed another gap in the humanoid fossil record by being the oldest known specimen with feet better suited for walking and smaller teeth as compared to chimpanzees.

    These fossils help show how humans came to acquire a large mental capacity. A modern chimpanzee's brain has a volume of 450 cubic centimeters as compared to a modern human with a volume of 1450 cubic centimeters. The fossils records of humanoids such as "Lucy" and "Ardi" so an increase in cranium volume over time. Also, the discovery of tools along Neanderthal fossils shows some proof that intelligence for the species was a selective advantage. Such fossil records show the divergence of a species with mental capacity away from the rest of the group.

    Scientists believe humans diverged from other Hominoidea approximately seven million years ago. Chimpanzees are believed to be the closest of the "Great Apes", sharing 98.5% of DNA with people. The "Great Apes" all have similar anatomies such as forward facing eyes, fingernails, color vision, and opposable thumbs. Since Homo sapiens are relatively different in appearance to the other members of Hominoidea, it would be assumed that the "missing link" would show greater resemblance to the chimpanzee than to a human. However, it is unrealistic to find fossil records of the "missing link" because determining which fossil is the "missing link" would require a complete fossil record of both chimpanzees and humans. This is unrealistic because the dry conditions of Africa are not prime for fossilization.

    Page 194-196 of "Why Evolution is True" by Jerry Coyne