Evolution

The theory of evolution states that the changes that affect organisms over time are driven by modifications in physical and behavioral traits

Evolution is change in the heritable characteristics of biological populations over successive generations. Evolutionary processes give rise to biodiversity at every level of biological organisation, including the levels of species, individual organisms, and molecules.

Repeated formation of new species (speciation), change within species (an agenesis), and loss of species (extinction) throughout the evolutionary history of life on Earth are demonstrated by shared sets of morphological and biochemical traits, including shared DNA sequences. These shared traits are more similar among species that share a more recent common ancestor, and can be used to reconstruct a biological "tree of life" based on evolutionary relationships (phylogenetics), using both existing species and fossils. 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 both by speciation and by extinction.

In the mid-19th century, Charles Darwin formulated the scientific theory of evolution by natural selection, published in his book On the Origin of Species (1859). Evolution by natural selection is a process first demonstrated by the observation that often, more offspring are produced than can possibly survive. This is followed by three observable facts about living organisms:

1) traits vary among individuals with respect to 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 replaced by progeny of parents better adapted to survive and reproduce in the biophysical environment in which natural selection takes place.

All life on Earth shares a common ancestor known as the last universal common ancestor (LUCA), which lived approximately 3.5–3.8 billion years ago. A December 2017 report stated that 3.45 billion-year-old Australian rocks once contained microorganisms, the earliest direct evidence of life on Earth. Nonetheless, this should not be assumed to be the first living organism on Earth; a study in 2015 found "remains of biotic life" from 4.1 billion years ago in ancient rocks in Western Australia. In July 2016, scientists reported identifying a set of 355 genes from the LUCA of all organisms living on Earth. More than 99 percent of all species that ever lived on Earth are estimated to be extinct. Estimates of Earth's current species range from 10 to 14 million, of which about 1.9 million are estimated to have been named and 1.6 million documented in a central database to date. 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.