Short answers, pulled from the story.
The term biology in its modern sense was introduced almost simultaneously by Thomas Beddoes in 1799, Karl Friedrich Burdach in 1800, Gottfried Reinhold Treviranus in 1802, and Jean-Baptiste Lamarck in 1802. Before this, the study of living things was divided among natural history, physiology, natural philosophy, and medicine.
Aristotle classified 540 animal species and personally dissected at least 50, making him the most influential scholar of the living world from classical antiquity. He pioneered systematic biological observation and introduced the concept of the scala naturae, or Great Chain of Being, which ranked creatures from plants to humans and dominated Western biological thought for nearly two thousand years.
The Neolithic Revolution, which occurred around 10,000 years ago, was when humans first deliberately cultivated plants for farming and domesticated livestock animals. It is considered the first major turning point in biological knowledge because it required and produced systematic understanding of plant and animal life.
James Watson and Francis Crick proposed the double helix structure of DNA in 1953, building on X-ray crystallography work by Maurice Wilkins and Rosalind Franklin. Their paper noted that the specific base-pairing they described immediately suggested a copying mechanism for the genetic material.
Mendel published his laws of inheritance in 1866, but the work was not recognized as significant for 35 years. It was only when Carl Correns and others rediscovered his findings around 1900 that the implications for genetics and evolutionary theory began to be understood.
Charles Darwin's On the Origin of Species, published in 1859, is often considered the central event in the history of modern biology. Darwin combined biogeographical evidence, uniformitarian geology, writings on population growth by Thomas Malthus, and his own morphological expertise to build the theory of evolution by natural selection, which most scientists accepted by the end of the 19th century.