The pioneers of cell theory got its third rule wrong
In 1838 Schleiden and Schwann championed two ideas every biology student now learns: organisms are built from cells, and each cell has all the features of life. But they rejected the third pillar, that cells arise only from other cells, still clinging to spontaneous generation. Robert Remak and Rudolf Virchow had to finish the job.
Biology is the science of living things, from molecules to whole ecosystems. It rests on five big themes: the cell as life's basic unit, genes as the basis of inheritance, evolution as the source of diversity, energy transformation to power living processes, and homeostasis, the upkeep of a stable internal state. The word joins the Greek bios, life, with logia, study, and appeared in a 1766 volume by Michael Christoph Hanow before several scholars adopted it independently around 1800, Lamarck among them.
The roots go back to ancient Egypt and Mesopotamia. Aristotle studied causation and the variety of life, while his successor Theophrastus founded the scientific study of plants. Writers in the medieval Islamic world, including al-Jahiz, carried the work forward. Then Anton van Leeuwenhoek's far better microscopes revealed bacteria, sperm cells and a teeming unseen world, and by the 1860s the full three-part cell theory had won general acceptance.
Classification and evolution came next. Carl Linnaeus published a taxonomy in 1735, and Buffon even hinted at common descent. Charles Darwin, drawing on Humboldt, Lyell and Malthus alongside his own observations, built a theory of evolution by natural selection, which Alfred Russel Wallace reached independently. Gregor Mendel's 1865 work on inheritance was overlooked until the early twentieth century, when the modern synthesis merged it with Darwin's ideas.
The molecular age followed. Alfred Hershey and Martha Chase ran experiments indicating that genes ride on DNA, and James Watson and Francis Crick described its double helix in 1953. Researchers then cracked the genetic code, and the Human Genome Project began in 1990. One striking later discovery is deep homology: the eyes of insects, vertebrates and cephalopod molluscs, long assumed to have evolved separately, are steered by similar genes. Theodosius Dobzhansky famously argued that no part of biology makes sense unless viewed through evolution.
Source: Biology
