Chapter 3: Genes Build Brains

• Introduction
• Evolution is random, not directed.
• Humans are what has survived, not the pinnacle.
• Other results were possible, we just happened to survive.
• How Much Variation can Occur?
• Basic Genetics
• Basic unit of a strand of DNA is a base pair.
• A group of 3 adjacent base pairs form a codon.
• Each codon maps to one of 20 amino acids.
• A string of codons (with a start and stop codon) make up a gene.
• A gene codes to a protein.
• Most of the DNA occurs outside genes (introns)
• There are around 25,000 genes in the human genome.
• Odd factoid
• Human and chimpanzee genomes differ by only about 3%.
• But one human being's genome may differ from another's by up to 12%.
• Which genes are varying is more important than the number of genes.
• Blueprint Systems
• Compares computer code to genes.
• Computer code is very brittle, i.e. changing a bit in a program could seriously impair the program
• Genes are more resilient
• Bundling Genes
• Variation is random, but it is constrained
• Genes are a sort of constrained language
• Makes them more resilient but also limits them
• Genes only code to viable combinations, not all combinations.
• Large Brains are Expensive
• Nervous tissue requires twice as many calories as others
• Note that 50% of that must come from carbohydrates
• Requires large animal at birth
• Increases risk to the mother
• If it is expensive, why do humans have them?
• Common theory is that intelligence is strongly selected for.
• Theory in this book
• Larger brain was an "accident"
• Larger brain had additional utility
• Then the species adapted to having larger and larger brains.