Human Diversity in a Nutshell By William Lama, Ph.D.
Human Diversity in a Nutshell
By William Lama, Ph.D.
British diplomats returning from China recounted a Chinese saying: “May you live in interesting times.” They took it as a curse with “interesting times” a euphemism for war. The Chinese disclaimed ownership of the curse, but indeed, the most fascinating periods in history were filled with tumult and upheaval. To be sure, the last century was “interesting.” There were two world wars, the Spanish Flu pandemic, the Great Depression, and the rise and fall of global communism. Political upheavals were robust and widespread. The 20th century was also filled with cultural and scientific upheaval. Who can forget the Chinese “Cultural Revolution” or Woodstock and the hippie counterculture in America? Not for nothing was the youth culture characterized by sex, drugs and rock n roll.
In science physics took center stage with new findings and theories that overturned centuries- old established laws. Einstein predicted that all motion is relative, that space-time is curved and that matter can be completely transformed into energy according to the formula formula E = mc^2. All of these remarkable predictions were soon validated. When astronomical measurements showed that the universe is uniformly expanding, Einstein was surprised that his General Relativity theory predicted that as well.
In the realm of the living, biology became a “hard science” following the discovery that the structure of the DNA molecule contains the genetic code that determines who we are. Even more remarkable is the fact that sociology is becoming a science. This despite the resistance of mainstream social scientists who cling to an orthodoxy that doesn’t recognize the importance of human biology. This fascinating story is told by Charles Murray in his new book.
Genetics define us
In order to follow Murray’s arguments some basic biological terms are needed. Genes are the key that distinguish our species. About 99% of our genes are shared with all other human beings. The 1% that are different determine who we are as individuals. To understand genes and genetics we must look to the DNA molecule. Its structure, (worked out by James Watson and Francis Crick in 1953) is a linked double helix composed of sugar and phosphate molecules. Between the helixes like rungs on a ladder are pairs of chemicals called nitrogenous bases: Adenine (A), Thymine (T), Guanine (G) and Cytosine (C). These bases link up in a very specific way: A always pairs with T, and C always pairs with G. The base pairs are loosely held together by Hydrogen bonds. The DNA molecule containing about 3 billion base pairs is found in the nucleus of every cell in your body. Sets of three of the four DNA bases are employed to encode the 20 standard amino acids used by living cells to build proteins. Some of the genetic code words (“codons”) include AAA which codes for phenylalanine, AAT codes for leucine, ACT codes for tryptophan and GGA codes for proline. The 4 bases taken 3 at a time allow a maximum of 4³ = 64 amino acids. However, most of the amino acids are coded for by two to six codons resulting in useful redundancy.
DNA Structure https://www.genome.gov/
DNA is the key to genetic diversity. Genes, the basic units of genetics, are lengths of DNA that determine the specific proteins to be produced by the cell.
Backbone__________________________________________________________
I I I I I I Base I
I I I I I I pairs I
site 3 4 5 3B
I…..chromosome ……………………….I ….
I..gene..I
Chromosomes are lengths of DNA containing many genes. Human beings have 23 pairs of chromosomes in every cell, 46 chromosomes in total. A child receives 23 chromosomes from mother and 23 from father. The sex chromosomes X and Y determine whether you are a boy (XY) or a girl (XX). The male Y chromosome contains a gene called “sry” (pronounced sorry for obvious reasons) that determines several gender differences.
The human genome contains about 23,000 genes in its 46 chromosomes. Chromosome 1, the largest, contains about 240 million base pairs in 8000 genes. Chromosome 21, the smallest, contains about 300 genes.
Human Genome Introduction to Genomics (genome.gov)
Vive la difference!
Of the 3 billion base pairs in the DNA of every human, the vast majority are common. However, there are human to human differences and these are the source of our diversity. Single nucleotide polymorphisms, or SNPs (pronounced “snips”) are the most common type of genetic variation among people. Each SNP represents a difference of a single base at a given site. For example, two DNA sequences from different individuals, AAGCCTAG to AAGCTTAG, contain a difference at a single site. In this case we say that there are two alleles: C and T. Almost all common SNPs have only two alleles. The figure below illustrates this case where the pair CG is replaced by TA.
The enormous variety of human traits depends on the diversity of genomes. A phenotype is an individual's observable traits, such as height, eye color, blood type, intelligence and personality. The genetic contribution to the phenotype is called the genotype.
Single-Nucleotide Polymorphism SNP
Welcome to ISOGG... | International Society of Genetic Genealogy
“The first law of behavioral genetics is that all psychological traits show a significant and substantial genetic influence.” (Robert Plomin, Blueprint: How DNA makes us who we are, Penguin Books, 2018) SNPs create genotype differences which produce different traits for different folks. How this works will require a second nutshell. Tune in next month.
Dr. William Lama has a PhD in physics from the University of Rochester. Taught physics in college and worked at Xerox as a principle scientist and engineering manager. Upon retiring, joined the PVIC docents; served on the board of the RPV Council of Home Owners Associations; served as a PV Library trustee for eight years; served on the PV school district Measure M oversight committee; was president of the Malaga Cove Homeowner's Association. Writes about science, technology and politics, mostly for his friends.
email: wlama2605@gmail.com