Evolution is any change across successive
generations in the inherited characteristics of biological populations.
Evolutionary processes give rise to diversity at every level of
biological organisation, including species, individual organisms and
molecules such as DNA and proteins.
Life on Earth originated and then evolved
from a universal common ancestor approximately 3.7 billion years ago.
Repeated speciation and the divergence of life can be inferred from
shared sets of biochemical and morphological traits, or by shared DNA
sequences.
These homologous traits and sequences are
more similar among species that share a more recent common ancestor,
and can be used to reconstruct evolutionary histories, using both
existing species and the fossil record.
Existing patterns of biodiversity have
been shaped both by speciation and by extinction. Charles Darwin was
the first to formulate a scientific argument for the theory of evolution
by means of natural selection.
Evolution by natural selection is a process that is inferred from three facts about populations:
1) more offspring are produced than can possibly survive,
2) traits vary among individuals, leading to differential rates of survival and reproduction, and
3) trait differences are heritable.
Thus, when members of a population die
they are replaced by the progeny of parents that were better adapted to
survive and reproduce in the environment in which natural selection took
place.
This process creates and preserves traits
that are seemingly fitted for the functional roles they perform.
Natural selection is the only known cause of adaptation, but not the
only known cause of evolution.
Other, nonadaptive causes of evolution
include mutation and genetic drift. In the early 20th century,
genetics was integrated with Darwin’s theory of evolution by natural
selection through the discipline of population genetics.
The importance of natural selection as a
cause of evolution was accepted into other branches of biology.
Moreover, previously held notions about evolution, such as orthogenesis
and “progress” became obsolete.
Scientists continue to study various
aspects of evolution by forming and testing hypotheses, constructing
scientific theories, using observational data, and performing
experiments in both the field and the laboratory.
Biologists agree that descent with
modification is one of the most reliably established facts in science.
Discoveries in evolutionary biology have made a significant impact not
just within the traditional branches of biology, but also in other
academic disciplines (e.g., anthropology and psychology) and on society
at large.
