Darwin's Theory of Evolution
Darwin's Theory of Evolution
Theory of Evolution
natural selection: those whose traits were less suited to the environment would die. Nature (the environment) selects individuals which use resources most efficiently; explanation of how species naturally change over time / "principle by which each slight variation [of a trait], if useful, is preserved"
Mutations: in DNA can change genes and produce variations in traits. Darwin was convinced that small, heritable variations in traits were common among individuals within a species and that these variations occur by chance.
Darwin reasoned that populations of all species have the capacity to grow. / Species produce more offspring than can survive. However, his observations showed that most populations remained stable due to environmental limits. For population sizes to remain stable, many offspring must die; "overproduction of offspring" / "struggle for existence"
adaptations happen over many generations within one lineage of organisms which result in a new species. overproduction of offspring, and differential survival and reproduction; in chance variation the proportion of individuals with a favorable trait (or favorable phenotype) will increase.
Differential survival and reproduction: long-necked giraffes could feed from taller trees = more likely to survive and produce more offspring. Short-necked giraffes had more competition for food and were more likely to starve before reproduction; Darwin showed that evolution is not goal-directed. Instead, the environment reinforces variations which occur by chance.
Charles Darwin's 1859 book On the Origin of Species
mutations in DNA can change genes and produce variations in traits: sexual reproduction increased variation
Adaptations relate to every aspect of life: food, water, oxygen, nutrients, shelter, growth, response, reproduction, movement, behavior, and ability to learn: increase chance of survival for at least some
. Biologist E.O. Wilson believes adaptations reach every aspect of human life - that social, political, and even religious behaviors are rooted in our genes.
Influences on Darwin
Charles Lyell (author of Principles of Geology) challenged belief that Earth was young; small changes over long periods of time built today’s landscapes and Earth must be far older than most people believed
inheritance of acquired characteristics: early giraffes stretched their necks to reach tall trees and then passed the longer necks on to their calves
Darwin’s idea that individuals in a population compete for resources came from reading Thomas Malthus; he described a human “struggle for existence”, due to exponential population growth and limited food:
Jean Baptiste Lamarck believed organisms improve traits through increased use and then pass the improved feature on to their offspring
Alfred Russel Wallace: sent a paper with concepts nearly identical to Darwin’s ideas about evolution + natural selection
Malthus did "On Population" essay
Darwin became a naturalist: boarded the H.M.S. Beagle (5 years)
Before Darwin, most people believed that all species were created at the same time and remained unchanged throughout history
Charles Robert Darwin (12 February 1809 - 19 April 1882) took him 23 years to publish
Darwin argued present life has arisen gradually from past life forms.