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The 2-hour special NOVA: What Darwin Never Knew is a concise overview of Charles Darwin's discovery of evolution by natural selection. The video describes in detail much of the work of Charles Darwin, as well as the modern biologists, medical researchers, paleontologists, and statisticians who have continued to investigate the origin of species.
The worksheet consists of 116 objective questions, mostly multiple choice and true or false. The questions will prompt the students to follow the progress of the video. This may sound like a lot, but I have found that this format enables the students to pay attention to the video while quickly recording their answers. I try to avoid a situation where the students are bogged down by writing long responses during a video.
The zip file download contains the 116 question video worksheet, 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.
NOVA: What Darwin Never Knew Summary
The publication of Charles Darwin’s On the Origin of Species in 1859 was a groundbreaking achievement in the history of science and biology. Darwin outlined a theory of evolution by natural selection, and he was able to document many of his claims using evidence collected while on the voyage of the HMS Beagle to South America and the Pacific Ocean. Other claims lacked corroboration, but later researchers are filling in the gaps of the effort that Darwin had started.
Darwin planned to study medicine, but was revolted by watching an operation on a child in the days before anesthetics. He switched to becoming a clergyman, but his passion for nature led him to a position on the HMS Beagle as a resident scientist. Darwin collected numerous samples on his voyage. For example, he documented the existence of extinct forms now found as fossils. He also collected numerous different types of birds from the isolated Galapagos Islands, and later realized that they were all the same type of animal, the finch, and that their apparent differences could be linked to the individual island upon which they had lived. Some birds required short, strong beaks for cracking nuts, others required long, thin beaks for consuming flower nectar. Darwin later speculated that an ancestral finch had made it to the Galapagos from the South American mainland, and that the birds later deviated and changed depending upon the individual circumstances on each island.
Darwin’s observation of embryos also provided further support for his theory. He observed that human embryos displayed structures analogous to fish gills, and that snake and whale embryos exhibited bumps related to the formation of legs, which are absent in the adult form. He was able to claim that land vertebrate animals evolved from early fishes, that snakes had evolved from a four-legged ancestor, and that whales had evolved from land mammals.
Darwin proposed a model of the development of earth’s life that consisted of a tree with an original ancestor at the bottom. All other resulting species later branched out in their own directions. In this model, any two species can eventually be linked to a single common ancestor somewhere on the Tree of Life.
The breeding of dogs provided for Darwin a well-known example of evolutionary change that had been caused by human intervention. Dogs, a single species, have been selectively bred into myriad forms, everything from Chihuahuas to Great Danes. Darwin suggested that human guided selective breeding resembles an enhanced and accelerated version of what occurs in nature, which he called natural selection. Darwin posited that the struggle for existence and variation in offspring combined to foster the survival of forms most advantageous for survival, and that these enhanced traits were more likely to be passed on to the next generation. In this way, positive changes accumulate and are promoted forward in time.
Despite the initial success of evolutionary theory, many aspects of the origin of species remained unexplained. Darwin did not actually know how evolution took place, and which biological structures were responsible for the transmission of positively selected features. The mysterious method of transfer was discovered in the twentieth century. The DNA molecule is found in the body cells of all life on earth, and it consists of a molecular alphabet that is used to store information that determines the body plan and other features of earth’s life.
DNA is grouped into sections termed genes, which are the individual units of heredity. During, for example, human conception, the fertilized egg receives half of its DNA from each parent, and this information is shuffled to create unique combinations. Mutation is another form of change in DNA. Mutations can often be favorable if they result in changes that help foster the survival of offspring. An example in the video is the pocket mouse, which has evolved dark fur to better survive on the intermittent patches of dark basaltic rock found in Arizona deserts.
A great wellspring of discovery has resulted from the Human Genome Project, an effort started in 1993 to map the entire genome of the human species. Since the completion of the project, human DNA can be compared to the DNA of other life forms in order to estimate the amount of evolutionary similarity between such disparate species as humans and chimps, or chimps and chickens, etc. An unexpected result of the Human Genome Project was that human DNA was found to have fewer genes than other seemingly more primitive forms such as the corn plant. Apparent complexity is not entirely determined by the evolution of new genes, but is likely caused by using older genes in new ways. Scientists have discovered sections of DNA that operate as switches that regulate the activation of other genes. Master genes also exist which are used to choreograph the overall body plan of an organism. Many of the genes found in living things are similar, yet evolution appears to have changed the timing and implementation of an essentially common set of genes to generate the myriad forms of life we see today.
Darwin’s theory of evolution by natural selection encountered great resistance, some of which continues to this day. Yet scientists realized that evolution provided wonderfully plausible explanations for the great diversity and distribution of life on earth, and it has been hugely successful. Darwin’s theory was also seen by some to attack religious beliefs about the special status of mankind as being made in the image of God. The theory also apparently conflicted with the creation story in Genesis, which had once been interpreted as claiming that earth’s life had resulted from individual acts of creation, and that each species was immutable and perfect.
Nothing was more controversial in evolutionary theory than the apparent descent of man from apes. Darwin was savaged for making this assertion. Despite this, the evidence for such human origins has grown exponentially. The ability to sequence DNA has shown that the DNA similarity between humans and chimpanzees, our closest relative in nature, is 99%. Amazingly, that 1% difference results in the essential differences that make us “human”.
The video describes in detail much of the work of Charles Darwin, as well as the modern biologists, medical researchers, paleontologists, and statisticians who have continued to investigate the origin of species. The video itself is based upon the works of University of Wisconsin evolutionary biologist Sean Carroll, who is researching the genome of fruit flies. Michael Nachman’s work studying pocket mice was mentioned above. Comparison of fish and manatee DNA has led to a description of how species such as snakes and whales were able to “turn off” the genes that grow legs. Cliff Tabin described his research into the genetic switches responsible for the differing beak morphologies of Darwin’s Galapagos finches. The discovery of archaeopteryx in Darwin’s time was the first known transitional fossil, and the linkages between dinosaurs and birds have been supported by other recent fossil discoveries. Neil Shubin discovered a remarkable transitional fossil named Tiktaalik, which appears to be an intermediate form between fish and four limbed, land-walking vertebrates. Shubin also studies the DNA of modern paddlefish which are thought to be “living fossils”, and which also exhibit similarities to the Tiktaalik fossil. Modern researchers such as Jim Noonan, Hansell Stedman, and Chris Walsh are striving to identify the specific genes needed to form the human brain. Katie Pollard is a biostatistician who used computer programs to narrow down the specific genetic differences between chimps and humans that has led to the evolution of the human brain.