what are the basic events of evolution
Answers
Evolution is the process of change in all forms of life over generations, and evolutionary biology is the study of how evolution occurs. Biological populations evolve through genetic changes that correspond to changes in the organisms' observable traits. Genetic changes include mutations, which are caused by damage or replication errors in organisms' DNA. As the genetic variation of a population drifts randomly over generations, natural selection gradually leads traits to become more or less common based on the relative reproductive success of organisms with those traits.
The age of the Earth is about 4.54 billion years.[1][2][3] The earliest undisputed evidence of life on Earth dates at least from 3.5 billion years ago,[4][5][6] during the Eoarchean Era after geological crust started to solidify, following the earlier molten Hadean Eon. Microbial mat fossils in 3.48 billion-year-old sandstone have been found in Western Australia.[7][8][9] Other early physical evidence of life includes graphite, a biogenic substance, in 3.7 billion-year-old metasedimentary rocks in western Greenland[10] and, in 2015, "remains of biotic life" found in 4.1 billion-year-old rocks in Western Australia.[11][12] According to one of the researchers, "If life arose relatively quickly on Earth ... then it could be common in the universe."[11] It is estimated that more than 99 percent of all species, amounting to over five billion species,[13] that ever lived on Earth are extinct.[14][15] Estimates on the number of Earth's current species range from 10 million to 14 million,[16] of which about 1.2 million have been documented and over 86 percent have not yet been described.[17] More recently, in May 2016, scientists reported that 1 trillion species are estimated to be on Earth currently with only one-thousandth of one percent described.[18]
Evolution does not attempt to explain the origin of life (covered instead by abiogenesis), but it does explain how early lifeforms evolved into the complex ecosystem that we see today.[19] Based on the similarities between all present-day organisms, all life on Earth is assumed to have originated through common descent from a last universal ancestor from which all known species have diverged through the process of evolution.[20] All individuals have hereditary material in the form of genes received from their parents, which they pass on to any offspring. Among offspring there are variations of genes due to the introduction of new genes via random changes called mutations or via reshuffling of existing genes during sexual reproduction.[21][22] The offspring differs from the parent in minor random ways. If those differences are helpful, the offspring is more likely to survive and reproduce. This means that more offspring in the next generation will have that helpful difference and individuals will not have equal chances of reproductive success. In this way, traits that result in organisms being better adapted to their living conditions become more common in descendant populations.[21][22] These differences accumulate resulting in changes within the population. This process is responsible for the many diverse life forms in the world.
The forces of evolution are most evident when populations become isolated, either through geographic distance or by other mechanisms that prevent genetic exchange. Over time, isolated populations can branch off into new species.[23][24]
The majority of genetic mutations neither assist, change the appearance of, nor bring harm to individuals. Through the process of genetic drift, these mutated genes are neutrally sorted among populations and survive across generations by chance alone. In contrast to genetic drift, natural selection is not a random process because it acts on traits that are necessary for survival and reproduction.[25] Natural selection and random genetic drift are constant and dynamic parts of life and over time this has shaped the branching structure in the tree of life.[26]
The modern understanding of evolution began with the 1859 publication of Charles Darwin's On the Origin of Species. In addition, Gregor Mendel's work with plants helped to explain the hereditary patterns of genetics.[27] Fossil discoveries in paleontology, advances in population genetics and a global network of scientific research have provided further details into the mechanisms of evolution. Scientists now have a good understanding of the origin of new species (speciation) and have observed the speciation process in the laboratory and in the wild. Evolution is the principal scientific theory that biologists use to understand life and is used in many disciplines, including medicine, psychology, conservation biology, anthropology, forensics, agriculture and other social-cultural applications.