The earliest of roots of science, which included medicine, can be traced to ancient Egypt and
Mesopotamia in around 3000 to 1200 BCE.[11][12] Their contributions later entered and shaped
Greek natural philosophy of classical antiquity.[11][12][13][14] Ancient Greek philosophers
such as Aristotle (384–322 BCE) contributed extensively to the development of biological
knowledge. His works such as History of Animals were especially important because they
revealed his naturalist leanings, and later more empirical works that focused on biological
causation and the diversity of life. Aristotle's successor at the Lyceum, Theophrastus, wrote a
series of books on botany that survived as the most important contribution of antiquity to the
plant sciences, even into the Middle Ages.[15]
Scholars of the medieval Islamic world who wrote on biology included al-Jahiz (781–869), Al-
Dīnawarī (828–896), who wrote on botany,[16] and Rhazes (865–925) who wrote on anatomy
and physiology. Medicine was especially well studied by Islamic scholars working in Greek
philosopher traditions, while natural history drew heavily on Aristotelian thought, especially in
upholding a fixed hierarchy of life.
Biology began to quickly develop and grow with Anton van Leeuwenhoek's dramatic
improvement of the microscope. It was then that scholars discovered spermatozoa, bacteria,
infusoria and the diversity of microscopic life. Investigations by Jan Swammerdam led to new
interest in entomology and helped to develop the basic techniques of microscopic dissection and
staining.[17]
Advances in microscopy also had a profound impact on biological thinking. In the early 19th
century, a number of biologists pointed to the central importance of the cell. Then, in 1838,
Schleiden and Schwann began promoting the now universal ideas that (1) the basic unit of
organisms is the cell and (2) that individual cells have all the characteristics of life, although they
opposed the idea that (3) all cells come from the division of other cells. However, Robert Remak
and Rudolf Virchow were able to reify the third tenet, and by the 1860s most biologists accepted
all three tenets which consolidated into cell theory.[18][19]
Meanwhile, taxonomy and classification became the focus of natural historians. Carl Linnaeus
published a basic taxonomy for the natural world in 1735 (variations of which have been in use
ever since), and in the 1750s introduced scientific names for all his species.[20] Georges-Louis
Leclerc, Comte de Buffon, treated species as artificial categories and living forms as malleable—
even suggesting the possibility of common descent. Although he was opposed to evolution,
Buffon is a key figure in the history of evolutionary thought; his work influenced the
evolutionary theories of both Lamarck and Darwin.[21]
In 1842, Charles Darwin penned his first sketch of On the Origin of Species.[22]
Serious evolutionary thinking originated with the works of Jean-Baptiste Lamarck, who was the
first to present a coherent theory of evolution.[23] He posited that evolution was the result of
environmental stress on properties of animals, meaning that the more frequently and rigorously
an organ was used, the more complex and efficient it would become, thus adapting the animal to
its environment. Lamarck believed that these acquired traits could then be passed on to the
animal's offspring, who would further develop and perfect them.[24] However, it was the British
naturalist Charles Darwin, combining the biogeographical approach of Humboldt, the
uniformitarian geology of Lyell, Malthus's writings on population growth, and his own
morphological expertise and extensive natural observations, who forged a more successful
evolutionary theory based on natural selection; similar reasoning and evidence led Alfred Russel
Wallace to independently reach the same conclusions.[25][26] Darwin's theory of evolution by
natural selection quickly spread through the scientific community and soon became a central
axiom of the rapidly developing science of biology.
The basis for modern genetics began with the work of Gregor Mendel, who presented his paper,
"Versuche über Pflanzenhybriden" ("Experiments on Plant Hybridization"), in 1865,[27] which
outlined the principles of biological inheritance, serving as the basis for modern genetics.[28]
However, the significance of his work was not realized until the early 20th century when
evolution became a unified theory as the modern synthesis reconciled Darwinian evolution with
classical genetics.[29] In the 1940s and early 1950s, a series of experiments by Alfred Hershey
and Martha Chase pointed to DNA as the component of chromosomes that held the trait-carrying
units that had become known as genes. A focus on new kinds of model organisms such as viruses
and bacteria, along with the discovery of the double-helical structure of DNA by James Watson
and Francis Crick in 1953, marked the transition to the era of molecular genetics. From the 1950s
onwards, biology has been vastly extended in the molecular domain. The genetic code was
cracked by Har Gobind Khorana, Robert W. Holley and Marshall Warren Nirenberg after DNA
was understood to contain codons. Finally, the Human Genome Project was launched in 1990
with the goal of mapping the general human genome. This project was essentially completed in
2003,[30] with further analysis still being published. The Human Genome Project was the first
step in a globalized effort to incorporate accumulated knowledge of biology into a functional,
molecular definition of the human body and the bodies of other organisms.
