Revolver is the seventh studio album by the English rock band the Beatles. It was released on 5 August 1966, accompanied by the double A-side single "Eleanor Rigby" / "Yellow Submarine". The album was the Beatles' final recording project before their retirement as live performers and marked the group's most overt use of studio technology to date, building on the advances of their late 1965 release Rubber Soul. It has since become regarded as one of the greatest albums in the history of popular music, with recognition centred on its range of musical styles, diverse sounds, and lyrical content.
The Beatles recorded Revolver following a three-month break from professional commitments at the start of 1966, and during a period when London was feted as the era's cultural capital. The songs reflect the group's interest in the drug LSD, Eastern philosophy and the avant-garde, lyrically addressing themes such as death and transcendence from material concerns. With no thoughts of reproducing their new material in concert, the band made liberal use of studio techniques such as automatic double tracking, varispeed, reversed tapes and close audio miking, in addition to employing instrumentation outside of their standard live set-up. Among its innovative tracks are the psychedelic "Tomorrow Never Knows", recorded using tape loops controlled on several machines simultaneously; "Eleanor Rigby", a meditation on loneliness featuring a string octet as its only musical backing; and "Love You To", a foray into Hindustani classical music. The sessions also produced a non-album single, "Paperback Writer" backed with "Rain".
In the United Kingdom, the album's fourteen tracks were gradually distributed to radio stations in the weeks before its release. In North America, Revolver was reduced to eleven songs by Capitol Records, with the omitted three instead appearing on the June 1966 LP Yesterday and Today. The release there coincided with the Beatles' final concert tour and the controversy surrounding John Lennon's remark that the band had become "more popular than Jesus". The album topped the Record Retailer chart in the UK for seven weeks and the US Billboard Top LPs list for six weeks. Critical reaction was highly favourable in the UK, but less so in the US.
Revolver is credited with expanding the scope of pop music and its changes in studio practice were soon adopted throughout the recording industry. It was influential in advancing principles espoused by the 1960s counterculture and in inspiring the development of genres such as psychedelic rock, electronica, progressive rock and world music. The album cover, designed by Klaus Voormann, combined Aubrey Beardsley-inspired line drawing with photo collage and won the 1967 Grammy Award for Best Album Cover, Graphic Arts. Aided by the 1987 international CD release, which standardised its content to the original Parlophone version, Revolver has surpassed Sgt. Pepper's Lonely Hearts Club Band in many critics' estimation as the Beatles' best album. It was ranked first in Colin Larkin's book All-Time Top 1000 Albums and third in Rolling Stone magazine's list of the "500 Greatest Albums of All Time". It has been certified platinum by the BPI for sales since 1994 and 5× platinum by the RIAA.
Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes that are passed on from parent to offspring during reproduction. Different characteristics tend to exist within any given population as a result of mutation, genetic recombination and other sources of genetic variation. Evolution occurs when evolutionary processes such as natural selection (including sexual selection) and genetic drift act on this variation, resulting in certain characteristics becoming more common or rare within a population. It is this process of evolution that has given rise to biodiversity at every level of biological organisation, including the levels of species, individual organisms and molecules.
The scientific theory of evolution by natural selection was proposed by Charles Darwin and Alfred Russel Wallace in the mid-19th century and was set out in detail in Darwin's book On the Origin of Species (1859). Evolution by natural selection was first demonstrated by the observation that more offspring are often produced than can possibly survive. This is followed by three observable facts about living organisms: 1) traits vary among individuals with respect to their morphology, physiology and behaviour (phenotypic variation), 2) different traits confer different rates of survival and reproduction (differential fitness) and 3) traits can be passed from generation to generation (heritability of fitness). Thus, in successive generations members of a population are more likely to be replaced by the progenies of parents with favourable characteristics that have enabled them to survive and reproduce in their respective environments. In the early 20th century, other competing ideas of evolution such as mutationism and orthogenesis were refuted as the modern synthesis reconciled Darwinian evolution with classical genetics, which established adaptive evolution as being caused by natural selection acting on Mendelian genetic variation.
All life on Earth shares a last universal common ancestor (LUCA) that lived approximately 3.5–3.8 billion years ago. The fossil record includes a progression from early biogenic graphite, to microbial mat fossils, to fossilised multicellular organisms. Existing patterns of biodiversity have been shaped by repeated formations of new species (speciation), changes within species (anagenesis) and loss of species (extinction) throughout the evolutionary history of life on Earth. Morphological and biochemical traits are more similar among species that share a more recent common ancestor, and can be used to reconstruct phylogenetic trees.
Evolutionary biologists have continued to study various aspects of evolution by forming and testing hypotheses as well as constructing theories based on evidence from the field or laboratory and on data generated by the methods of mathematical and theoretical biology. Their discoveries have influenced not just the development of biology but numerous other scientific and industrial fields, including agriculture, medicine and computer science.