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Chapter 11: EvolutionEvolution combines random events, possibilities, probabilities, populations, and traits.
Traits are characteristics seen in individuals and shared usually in a population of similar individuals. Some are visible like skin colour, size, and motion. Some are invisible but easily identifiable like blood type, pH, and temperature. Some are difficult to discern like resistance to infection, endurance, and vulnerability of body parts like the heart or to cancer.
Traits are affected by genes and life experiences. A child might be born with genes for tallness but malnutrition when young could prevent those genes from being fully expressed. The connections between genes and life experiences are complex and vary for each trait. Many traits depend on several genes.
Within the first hundred million years of life, living things developed a very reliable system of copying genes for the creation of growth and new individuals. The error rate for this system is very low, perhaps less than 1 error in a billion replications (a replication is the copying of a chromosome with its included set of genes, mostly made of DNA.
Most mistakes either make very little, if any, difference, or are harmful or even lethal. Fewer than 1% of errors are helpful, but those errors contribute to populations changing.
Populations contain individuals that are similar but usually have variations that might be visible or invisible due to differences in some of their genes.
These differences provide the population with the potential for resiliency in responding to changes in their circumstances. If a critical change leads to a circumstance where survival is easier with certain differences, individuals with those differences will have a better chance to survive the change and reproduce. Individuals with differences that are unlikely to survive the change will disappear from the population. Individuals cannot adapt genetically to changes. Populations adapt to changes.
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