The Sense of Self by Richard W. Sears

Author:Richard W. Sears
Language: eng
Format: epub
Publisher: Palgrave Macmillan UK, London

Evolutionary Biology

In 1858, Charles Darwin and Alfred Wallace published a journal article entitled, “On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection” (Darwin and Wallace 1858), which was quickly followed by Darwin’s classic book, On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life (Darwin 1859). Their work sparked a flurry of scientific activity and research to explain how human beings came to be (Costa 2014).

Human beings had already recognized for centuries that certain qualities could be artificially selected for by breeding animals or plants with the most desirable qualities. In the mid-1800s, Gregor Mendel scientifically investigated heritability, and coined the terms “recessive” and “dominant” in regard to certain traits. His work laid the foundation for the field of genetics, which investigates how certain traits are passed along from generation to generation (Hartwell et al. 2015; Mukherjee 2016).

The work of Watson and Crick (1953) on the structure of deoxyribonucleic acid (DNA) provided a biological explanation for the previously mysterious mechanisms of genetics. Amazingly, only four nucleotide molecules (cytosine, guanine, adenine, and thymine), joined together in a specific sequence in a double-helix strand, contain all the information necessary to grow a human being or any other life form on Earth (Bronowski 1974; Futuyma 2006; Gould 1993; Pierotti 2010; Shapiro 2011). In a fairly new field known as epigenetics, scientists are studying the external and environmental factors that turn certain genes on and off (Allis et al. 2015; Carey 2013).

Early in the study of evolution, many believed organisms changed very smoothly and steadily, a concept known as phyletic gradualism (Sepkoski 2012). However, closer investigations of the fossil record showed evidence of “punctuated equilibrium,” times when evolutionary branches changed relatively quickly, often due to major events like meteor strikes or major volcanic activity (Eldredge and Gould 1972).

The molecular ingredients for life were present on the early Earth, and many of them were likely brought by comets as the Earth was newly forming (Pierazzo and Chyba 2010; Sagan and Druyan 1985) (Fig. 5.4). In the 1950s, Stanley Miller and Harold Urey first began experimenting with how organic chemicals could have formed from common inorganic chemicals (Miller 1953; Miller and Urey 1959). Basically, they put water (H2O), methane (CH4), ammonia (NH3), and hydrogen (H2) into a flask, sparking it with electricity (to simulate lightning), and produced amino acids, the building blocks of life, in only a week. Later experiments confirmed that even the building blocks of DNA can form relatively quickly from the chemicals that were likely to exist on the early Earth, and these chemicals are fairly abundant in the universe (Cleaves et al. 2008; Fox 1965; Jain 2015; Oró and Kimball 1961; Oró and Kamat 1961; Ruiz-Mirazo et al. 2014; Seeds and Backman 2016).

Fig. 5.4Comet Halley (W. Liller, Easter Island, International Halley Watch Large Scale Phenomena Network/NASA)

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