My Personal Summary
This book presents evidence for why evolution is true.
The fossil record shows that current species evolved from older species and evolution by natural selection is the most likely explanation for this based on extensive evidence.
- “The idea of natural selection is not hard to grasp. If individuals within a species differ genetically from one another, and some of those differences affect an individual’s ability to survive and reproduce in its environment, then in the next generation the “good” genes that lead to higher survival and reproduction will have relatively more copies than the “not so good” genes. Over time, the population will gradually become more and more suited to its environment as helpful mutations arise and spread through the population, while deleterious ones are weeded out. Ultimately, this process produces organisms that are well adapted to their habitats and way of life.”
- The fossil record shows that current species evolved from older species.
- Examples of imperfect design (like the appendix in humans or weird shaped veins in giraffes) are evidence against an intelligent creator and evidence for evolution.
- The fact that most species on islands are ones that can travel great distances over seas and the fact that species most similar to them are located on nearby continents is evidence for evolution because why would an intelligent creator only put those species on islands?
- Three things are needed for natural selection to produce an adaptation:
- (1) There has to be variation in the population of a species – i.e. mice with different colored coats
- (2) The variation must be based on genetics so the genes can be passed on to offspring
- (3) The genetic variation must affect an individual’s probability of leaving offspring. When these conditions are present, then the individuals with genetic advantages that survive at higher rates pass on their genes to offspring. Natural selection is literally just the environment changing the overall gene pool of a species, i.e. mice with light coats survive better in sandy beach areas because they’re less seen by predators so over time the dark colored mice die out and fail to pass on their dark genes to offspring. This is evolution by natural selection.
- An example of evolution in the real-world: Finches on a certain island in the Galapagos experienced a drought one year and the only seeds available to eat happened to be larger ones that could only be broken and eaten by finches with larger beaks. Thus, many finches with smaller beaks starved and the next generation of finches on the island had beaks that were 10% larger than the previous generation. This change in beak size is an example of evolution in real time.
- Another example of evolution in the real-world: viruses often have mutations that cause them to be resistant to antibiotics. These viruses are able to replicate more often, which explains why antibiotics eventually become useless to treating viruses and new ones must be developed by pharmaceutical companies.
- New species evolve when one species is split by some geographic barrier (like a mountain range, landslide, glacial movements, rivers, etc.) and evolves in two different directions based on the environment they happen to be in. After hundreds of thousands of years of being separated, there are two separate species that, even if introduced together, could not interbreed because their genes have become too different.
- This splitting of species over millions of years has produced the ~10 million different species on earth today.