July 18, 1635

Microscope manufactured by Christopher Cock of London for Robert Hooke. Hooke is believed to have used this microscope for the observations that formed the basis of Micrographia.

On this date, the English natural philosopher, inventor, architect, and mathematician Robert Hooke was born at Freshwater on the Isle of Wight. Hooke is most famous in biology for his book Micrographia, published in 1665. He devised the compound microscope and illumination system shown above, one of the best such microscopes of his time. With it Hooke observed organisms as diverse as insects, sponges, bryozoans, foraminifera, and bird feathers. Micrographia was an accurate and detailed record of his observations, illustrated with magnificent drawings. It was a best-seller of its day. Interestingly, it was in Micrographia that Hooke gave the word “cell” its meaning in biology by describing a slice of cork he examined under the microscope:

…I could exceedingly plainly perceive it to be all perforated and porous, much like a Honey-comb, but that the pores of it were not regular…these pores, or cells,…were indeed the first microscopical pores I ever saw, and perhaps, that were ever seen, for I had not met with any Writer or Person, that had made any mention of them before this…

Hooke had discovered plant cells — more precisely, what Hooke saw were the cell walls in cork tissue, which reminded him of the cells of a monastery.

In addition, Hooke is famous in paleontology. In the seventeenth century, a number of hypotheses had been proposed for the origin of fossils. One widely accepted explanation, going back to Aristotle, stated that fossils were formed and grew within the Earth. A shaping force, or “extraordinary Plastick virtue,” could thus create stones that looked like living beings but were not. However, Hooke examined fossils with a microscope — the first person to do so — and noted close similarities between the structures of petrified wood and fossil shells on the one hand, and living wood and living mollusk shells on the other. He concluded in Micrographica that such fossils were actually the remains of once-living organisms:

this petrify’d Wood having lain in some place where it was well soak’d with petrifying water (that is, such water as is well impregnated with stony and earthy particles) did by degrees separate abundance of stony particles from the permeating water, which stony particles, being by means of the fluid vehicle convey’d, not onely into the Microscopical pores…but also into the pores or Interstitia…of that part of the Wood, which through the Microscope, appears most solid…

Furthermore, in his Discourse of Earthquakes, published two years after his death, Hooke correctly concluded that many fossils represented organisms that no longer existed on Earth:

There have been many other Species of Creatures in former Ages, of which we can find none at present; and that ’tis not unlikely also but that there may be divers new kinds now, which have not been from the beginning.

Thus, Hooke realized, two and a half centuries before Darwin, that the fossil record documents changes among the organisms on the planet, and that species have both appeared and gone extinct throughout the history of life on Earth.

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