Behave: The Biology of Humans at Our Best and Worst

In this chapter, Sapolsky provides an introduction to the science of genetics and coverage of how our individual genome influences our behavior. For those unfamiliar with genetics, Sapolsky suggests reading Appendix 3.

Genes from the Bottom Up

Genes are hugely important to how the human body is organized, but the cultural conversation around genetics often exaggerates their importance to the idea that genes decide everything about us. In fact, environment plays a large role in “deciding” what genes “decide.”

Genes specify the shape, structure, and function of proteins, which are the building blocks of the human body. However, genes do not themselves decide when to “turn on” and start building. Instead, genes are turned on by transcription factors (TFs) which bind to “promoters,” the on switch at the head of the gene on the DNA strand. TFs activate due to environmental factors including those local to the gene, inside the whole of the organism, and the outside world. This can be understood in terms of an if/then clause: “If you smell your baby, then activate the oxytocin gene” (227), which triggers milk release in the breast. If you don’t smell the baby, no oxytocin, no milk release. Environmental inputs also cause TFs to be blocked from binding to promoters,

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