A new book has just been published on evolution: Daniel Fairbanks’ Evolving: The Human Effect and Why It Matters. Fairbanks is a noted DNA biologist at Utah Valley University, and also the author of the 2007 book Relics of Eden: The Powerful Evidence of Evolution in Human DNA.
In this book, Fairbanks presents a fairly broad overview of modern evolutionary theory, including evidence from human anatomy, from the fossil record (geology and paleontology), from the human genome (in substantial detail), and, finally, in the ongoing “arms race” between farmers and agricultural scientists on one hand, and increasingly sophisticated pests and pathogens on the other.
Comparisons between human anatomy and those of other living and extinct creatures are quite telling. The human spine was clearly adapted from four-footed creatures, as exhibited by the back problems that afflict millions of humans. Precursors of our wrists and ankles are clearly seen in the fossil record.
Vitamin C (ascorbic acid) is required for a wide range of essential metabolic reactions, and is produced by all mammalian species, with the notable exception of humans and some other closely related primates. Scurvy, that scourge of British seamen, and of Mormon pioneers crossing the Great Plains, results when humans don’t get enough Vitamin C. Curiously, while humans have the same overall biochemical machinery that produces Vitamin C in other mammals, it doesn’t work because mutations have inactivated a key final step. Evidently these mutations occurred after our primate ancestors adopted a diet rich in fruits and vegetables, so that when some individuals lost the ability to generate their own Vitamin C, it was not deleterious to their survival, and the trait was passed on to posterity.
Another interesting anomaly is the human eye. In human eyes (and indeed the eyes of all other vertebrates), the optic nerves emerge from the front of the retina, and then travel to the back, resulting in a blind spot, which can be demonstrated by a simple test involving marks on a card. By contrast, the eyes of cephalopods (including the octopus, squid, cuttlefish and nautilus) are designed more logically with nerve connections on the back of the retina. Again, the human design is a historical artifact from a stage early in the evolution of vertebates.
Some of the most dramatic evidence of evolution comes from recent studies in DNA (which is, in fact, Fairbanks’ specialty). For example, scientists noted long ago that humans have only 23 pairs of chromosomes, whereas other great apes (chimpanzees, bonobos, gorillas and orangutans) have 24. Thus they were led to conjecture that two of the human chromosomes have fused since the split between ancestral human and ape lineages. This hypothesis gained credence in 1982, when scientists found that chromosomes from humans, chimpanzees, gorillas and orangutans are highly similar and can be aligned with one another, with human chromosome #2 corresponding to the slightly overlapped union of ape chromosomes 2A and 2B. The final confirmation came in 1991 from a detailed analysis of human DNA, which found two complementary telomeres (repeated sequences of a certain DNA string that normally appear only at the end of a chromosome) spanning the exact spot of union:
Fusion site
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... TTAGGGG TTAGGG TTAG CTAA CCCTAA CCCTAA ...
... AATCCCC AATCCC AATC GATT GGGATT GGGATT ...
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(Note that the second row is a almost exactly a reversal of the first, pivoted about the fusion site.)
As it turns out, there are numerous other examples of chromosome rearrangements in the human genome. Inversions (where a segment of DNA consisting of hundreds of thousands or millions of base pairs is inverted) have occurred within several of our chromosomes, and can be employed as a means of understanding our species’ evolutionary history. For example, there are nine inversions that distinguish human and chimpanzee chromosomes, each of which must have arisen in either the human or chimpanzee ancestral lineage after these two lineages diverged. Comparisons with other primates show that inversions that have been identified in human chromosome 1 and 18 occurred exclusively in the human lineage, while those in chromosomes 4, 5, 9, 12, 15, 16 and 17 happened exclusively in the chimpanzee lineage. Numerous other such examples are given in Fairbank’s latest book.
Fairbanks summarizes as follows:
The evidence of ancient and ongoing human evolution is overwhelming. The examples in this book are merely a select few of thousands that fill volumes of scientific journals, and the number of examples continues to grow as evolutionary biologists publish new discoveries. Beyond the evidence of our own evolution, we’ve seen how an understanding of our place in evolution helps improve our health, feed our growing population, and protect our environment. These are practical reasons for studying evolution. They illustrate why evolution matters for the future of our planet and for our quality of life.