Behave: The Biology of Humans at Our Best and Worst
Page 72
Just for everyone’s sanity, I’m going to mostly ignore RNA. For our purposes, what is interesting is what genes, the starting point, have to do with their end products—proteins and their functions.
MUTATIONS AND POLYMORPHISMS
Genes are inherited from your parents (half the genes from each [not entirely true, as covered in the main text]). Suppose that when someone’s DNA genome is being copied for inclusion in their egg or sperm, a mistake is made in the copying of one single nucleotide; with billions of nucleotides, that’s bound to happen sometimes. As a result, unless corrected, the gene, now with its nucleotide sequence erroneously differing in one spot, is passed on to an offspring. This is a mutation.
In classical genetics there are three types of mutations that can occur. The first is called a point mutation. One single nucleotide is copied incorrectly. Will this change the amino acid sequence of the protein coded for? It depends. Back to redundancy in the DNA code, from a few paragraphs ago. Suppose there is a codon in a gene with the sequence GCT, coding for alanine. But there has been a mutation, yielding GCA instead. No problem—that still codes for alanine. It’s an inconsequential, “neutral” mutation. But suppose the mutation instead was GAT. This codes for a completely different amino acid called asparagine. Uh-oh.
In actuality, though, this may not be a big deal, if the new amino acid looks a lot like the one that was lost. Suppose you have a nucleotide sequence coding for the following metaphorical amino acid sequence:
“I/am/now/going/to/do/the/following”
Thanks to a subtle mutation, there is a change of one amino acid, but one without a ton of consequences:
“I/am/now/going/ta/do/the/following”
This would still be comprehensible to most people; the protein would merely be perceived as coming from New York. Translated into protein-ese, the protein has a slightly different shape and does its usual task a bit differently (maybe a little slower or faster). Not the end of the world.
But if the mutation codes for an amino acid that produces a protein with a dramatically different shape, the consequences can be enormous (even fatal).
Back to
“I/am/now/going/to/do/the/following”
What if there is a mutation in a nucleotide helping to code for the first w, a mutation with a big consequence?
“I/am/not/going/to/do/the/following”
Trouble.
The next type of classical mutation is called a deletion mutation. In this scenario a copying error is made during the inheritance of a gene. But instead of a nucleotide being miscopied, it is deleted. For example, in a case where the seventh nucleotide is deleted,
“I/am/now/going/to/do/the/following”
becomes
“I/am/now/oingt/od/ot/hef/ollowing”
This can frameshift everything over to generate gibberish, or even a different message (e.g., “For dessert I’d like the mousse” mutating to “For dessert I’d like the mouse”).
Deletion mutations can involve the loss of more than a single nucleotide. At an extreme, this can involve the deletion of the entire gene, or even a stretch of genes on a particular chromosome. Definitely not good.
Finally, there are insertion mutations. During copying of the DNA to pass on to the next generation, a nucleotide is inadvertently copied twice, duplicated. Thus:
“I/am/now/going/to/do/the/following”
becomes
“I/am/now/ggoin/gt/od/oth/efollowin”
Gibberish, or perhaps a different message, as in the following case, where an e has been inserted near the end of the string of letters: “Mary turned John down for a date because she did not enjoy boweling.” In some cases an insertion mutation can involve the insertion of more than a single nucleotide. At an extreme, this can even involve the duplication of an entire gene.
Point, deletion, and insertion mutations are most of what mutations are about.* Deletion and insertion mutations often have major consequences, usually deleterious, but sometimes produce a new, interesting protein.
Back to point mutations. Consider one that results in the substitution of a single amino acid in the protein, one that works a bit differently from the correct amino acid. As noted above, as a result, the protein still does its old job, but maybe does it a bit faster or slower. This could be the grist for evolutionary change—if the new version is disadvantageous, reducing the reproductive success of anyone who carries it, it will be gradually selected against, removing it from a population. If instead the new version is more advantageous, it will gradually replace the old one in a population. Or if the new version works better than the original in some circumstances but worse in others, it may reach equilibrium in the population with the original version, where a certain percentage of people have the old version, the remainder the new. In this case the particular gene would be described as coming in two different forms or variants, as coming with two different “alleles.” Most genes come with multiple alleles. And the result is individual variation in the functioning of genes (this is covered in far more complexity in chapter 8).
Finally, a clarification of the confusion where two sound bites about genetics collide. The first is that, on the average, full (non–identical twin) siblings share 50 percent of their genes.* The other is that we share 98 percent of our genes with chimps. So are we more related to chimps than to our siblings? No. Comparisons between humans and chimps are about types of traits—we both have genes coding for traits related to having, for example, eyes, muscle fibers, or dopamine receptors, and both lack genes related to having, for example, gills, antennae, or flower petals. So there’s 98 percent overlap at that level of comparison. But comparison between any two humans is about versions of those traits—both have a gene that codes for, say, this thing called eye color, but do they share the version that codes for the same particular color? Same for blood type, type of dopamine receptor, and so on. We have 50 percent overlap with siblings at this level of comparison.
Glossary of Abbreviations
ACC
anterior cingulate cortex
ACTH
adrenocorticotropic hormone
ADHD
attention-deficit/hyperactivity disorder
AIS
androgen insensitivity syndrome
APA
American Psychological Association
ASD
autism spectrum disorders
BDNF
brain-derived neurotrophic factor
BLA
basolateral amygdala
BMI
body mass index
BNST
bed nucleus of the stria terminalis
CAH
congenital adrenal hyperplasia
CBT
cognitive behavioral therapy
COMT
catechol-O-methyltransferase
CRH
corticotropin-releasing hormone
DAT
dopamine transporter
DHEA
dehydroepiandrosterone
dlPFC
dorsolateral PFC
DZ
dizygotic
EEA
equal environment assumption
EEG
electroencephalographic; EEGs electroencephalograms
ERPS
event-related potentials
fMRI
functional magnetic resonance imaging
FTD
frontotemporal dementia
GABA
gamma-aminobutyric acid
GnRH
gonadotropin-releasing hormone
GSR
galvanic skin resistance
GWAS
genomewide association studies
HG
hunter-gatherer
HH
high-warmth/high-competence
HL
high warmth/low competence
IAT
Implicit Association Test
LH
low warmth/high competence
LH
luteinizing hormone
LL
low warmth/low competence
LTD
long-term depression
LTP
long-term potentiation
MAO-A
monoamine oxidase-A
MHC
major histocompatibility complex
MZ
monozygotic
NCAM
neural cell adhesion molecule
PAG
periaqueductal gray
PD
Prisoner’s Dilemma
PFC
prefrontal cortex
PMC
premotor cortex
PMDD
premenstrual dysphoric disorder
PMS
premenstrual syndrome
PNS
parasympathetic nervous system
PTSD
post-traumatic stress disorder
PVN
paraventricular nucleus
RNA
ribonucleic acid
RWA
right-wing authoritarianism
SDO
social-dominance orientation
SES
socioeconomic status
SHRP
stress hyporesponsive period
SNPs
single-nucleotide polymorphisms
SNS
sympathetic nervous system
SPE
Stanford Prison Experiment
SSRI
selective serotonin reuptake inhibitor
STG
superior temporal gyrus
TF
transcription factor
TH
tryptophan hydroxylase
ToM
Theory of Mind
TPJ
temporoparietal juncture
TRC
truth and reconciliation commission
vlPFC
ventrolateral prefrontal cortex
vmPFC
ventromedial PFC 54
Abbreviations in the Notes
In order to save forests’ worth of paper, references cite only the first one or two authors. The following abbreviations are used for entire journal titles or words within them:
AEL: Applied Economics Letters. AGP: Archives of General Psychiatry. Am: American. AMFP: American Journal of Forensic Psychology. Ann: Annual. ANYAS: Annals of the New York Academy of Sciences. Arch: Archives of. ARSR: Annual Review of Sex Research. BBR: Behavioral Brain Research. BBS: Behavioral and Brain Sciences. Behav: Behavior or Behavioral. Biol: Biology or Biological. Biol Lett: Biology Letters. BP: Biological Psychiatry. Brit: British. Bull: Bulletin. Clin: Clinical. Cog: Cognitive or Cognition. Comp: Comparative. Curr: Current. Dir: Directions in. EHB: Evolution and Human Behavior. Endo: Endocrinology. Evol: Evolution. Eur: European. Exp: Experimental. Front: Frontiers in. Horm Behav: Hormones and Behavior. Hum: Human. Int: International. J: Journal or Journal of. JAMA: Journal of the American Medical Association. JCP: Journal of Comparative Psychology. JEP: Journal of Economic Psychology. JESP: Journal of Experimental and Social Psychology. JPET: Journal of Pharmacology and Experimental Therapeutics. JPSP: Journal of Personality and Social Psychology. JSS: Journal of Sports Sciences. Med: Medical or Medicine. Mol: Molecular. Nat: Nature. NEJM: New England Journal of Medicine. Neurobiol: Neurobiology. Neurol: Neurology. Nsci: Neuroscience or Neurosciences. Nsci Biobehav Rev: Neuroscience and Biobehavioral Reviews. PLoS: Public Library of Science. PNAS: Proceedings of the National Academy of Science, USA. PNE: Psychoneuroendocrinology. Primat: Primatology. Proc: Proceedings of the. Prog: Progress in. PSPB: Personality and Social Psychology Bulletin. PSPR: Personality and Social Psychology Review. Psych: Psychology or Psychological. Rep: Report or Reports. Res: Research. Rev: Review or Reviews. SCAN: Social, Cognitive and Affective Neuroscience. Sci: Science or Sciences. Sci Am: Scientific American. Soc: Society or Social. TICS: Trends in Cognitive Sciences. TIEE: Trends in Ecology and Evolution. TIGS: Trends in Genetic Sciences. TINS: Trends in Neuroscience.
Notes
Introduction
1.R. Byrne, “Game 21 Adjourned as Thrust and Parry Give Way to Melee,” New York Times, December 20, 1990.
2.For reviews of these two “easy” topics, see M. Winklhofer, “An Avian Magnetometer,” Sci 336 (2012): 991; and L. Kow and D. Pfaff, “Mapping of Neural and Signal Transduction Pathways for Lordosis in the Search for Estrogen Actions on the Central Nervous System,” BBR 92 (1998): 169.
3.J. Watson, Behaviorism, 2nd ed. (New York: Norton, 1930).
4.Footnote: J. Todd and E. Morris, eds., Modern Perspectives on John B. Watson and Classical Behaviorism (Westport, CT: Greenwood Press, 1994); H. Link, The New Psych of Selling and Advertising (New York: Macmillan, 1932).
5.E. Moniz, quoted in T. Szasz, Schizophrenia: The Sacred Symbol of Psychiatry (Syracuse, NY: Syracuse University Press, 1988).
6.K. Lorenz, quoted in R. Learner, Final Solutions: Biology, Prejudice, and Genocide (University Park: Penn State Press, 1992).
7.For discussions of Lorenz’s activities during the Nazi era, see B. Sax, “What is a ‘Jewish Dog’? Konrad Lorenz and the Cult of Wildness,” Soc and Animals 5 (1997): 3; U. Deichman, Biologists Under Hitler (Cambridge MA: Harvard University Press, 1999); and B. Müller-Hill, Murderous Science: Elimination by Scientific Selection of Jews, Gypsies, and Others, Germany 1933–1945 (Oxford, UK: Oxford University Press).
8.The
Wellesley effect was first reported by Martha McClintock of the University of Chicago: M. McClintock, “Menstrual Synchrony and Suppression,” Nat 229 (1971): 244. While a number of studies have replicated the Wellesley effect, some have not, as summarized in H. Wilson, “A Critical Review of Menstrual Synchrony Research,” PNE 17 (1992): 565. A critique of that critique can be found in M. McClintock, “Whither Menstrual Synchrony?” ARSR 9 (1998): 77.
9.V. S. Naipaul, Among the Believers: An Islamic Journey (New York: Vintage Books, 1992). And for the definitive book on this entire field of behavioral biology, see M. Konner, The Tangled Wing: Biological Constraints on the Human Spirit (New York: Henry Holt, 2003). This is the finest book in existence on the biology of human social behavior—subtle, nuanced, nondogmatic, and wonderfully written—by the anthropologist/physician Mel Konner. To my vast good fortune, Konner was my academic adviser and mentor when I was an undergraduate, and he has had the greatest intellectual impact on me of anyone in my life. Those who know Mel will recognize his intellectual imprint on every page of this book.