Spontaneous generation

After earlier uncertainty, Leeuwenhoek resisted the idea of spontaneous generation for over three decades.

  • 1679 June 13 (Letter L-088) to Lambert van Velthuysen

Nor can I understand how any little animal can originate without fertilization.

  • 1680 June 14 (Letter L-108) to Thomas Gale

He demonstrated that no living little animals originate in an infusion of pepper kept in an hermetically closed tube.

  • 1680 November 12 (Letter L-111) to Robert Hooke (my emphasis)

We can now be assured sufficiently that no animals, however small they may be, take their origin in putrefaction, but exclusively in procreation. For seeing that animals, from the largest down to the little despised animal, the flea, have little animals in their semen, seeing also that some of the vessels of the lungs of horses and cows consist of rings and that these rings also occur on the flea's veins, why cannot we come to the conclusion that as well as the male sperm of that large animal the horse and similar animals, and of all manner of little animals, the flea included, is furnished with animalcules (and other intestines, for I have often been astonished when I beheld the numerous vessels in a flea), why, I say should not the male sperm of the smallest animals, smaller than a flea, nay even the very smallest little animals have the perfection that we find in a flea.

  • 1686 May 14 (Letter L-175) to Members of the Royal Society

For I am unshakebly convinced that no live animals, whether worms, flies, fleas, lice - nay, not even mites - can be generated from the sap or the leaves of any tree or plant, or from any decayed or putrified matter, or from sweat. To satisfy myself in this respect I took some veal, more than two years ago, and put it into several glass tubes which I closed by the heat of fire, and left them standing in the sun in front of the windows as well as in other places, which caused the flesh to change partly into a watery fluid. I examined this meat and this fluid many times with the very greatest care, now and then opening the glass tubes and closing them again, and keeping a record of this. But never have I been able to discover any living creature in it.

I am quite aware that there are many people who firmly believe, and maintain not only that vermin can develop from decayed matter, but even that lice may originate from sweat. When, some time ago, a certain eminent and learned gentleman wanted to affirm this to me, saying that he had seen several instances of it, I replied that this was pure imagination. I was absolutely certain that it was just as impossible for a louse or a flea to come into being without procreation as it was for a horse or an ox, or some such animal to be born from the decay and corruption of a dung heap. Although we provide our body with clean linen more than once a week, and imagine that we do not associate with people who have lice, yet we can get such vermin from our maidservants, or from those who make our beds, and who have the said vermin, and might very easily pass some of it on to the bed linen. The gentleman in question was satisfied with this last remark, and I heard afterwards that he had dismissed one of his maids, because she was full of lice.

  • 1687 August 6 (Letter L-190) to Members of the Royal Society

Some persons have been doing their utmost to make me believe that the calander and the wolf (... both well-known everywhere in this country among corn merchants and bakers) are generated without reproduction.

The principal reasons that those people adduced were these:

The wheat, having been carried to a new loft, where no wheat has ever lain before, gets the calander growing inside it, and this must happen without any propagation.

On the other hand, they say:

We may open up a lot of wheat that is quite sound and uninjured, without there being the slightest tiny hole on the outside, and there will be an adult, living calander sitting inside it.

I have tried to convince them by reasoning, and I said, among other things, that we might easily, without knowing it, carry this vermin from one loft to another.

For, only let a worker who stirs the corn, leave a corn loft where there is calander, and the same may very easily carry a few wheat grains with the calander inside, or the calander itself, along with him, either on his clothes or his boots, without knowing it, to a loft where no calander had been before.

And on the other hand, the ship, waggon or cart, in which the corn was transported, may be infested with calanders, because of having previously carried grain in which there had been calanders. From those few transmitted calanders, the calander may be generated by propagation.

I might add several more of my notes, which I kept while shutting up and observing the calanders, to this letter. But I believe that what I have related here is sufficient to prove to Your Honours, and to all learned intellects, that the calanders cannot originate in any other way than through propagation. Namely, a calander mates, lays eggs, and worms come forth from those eggs, and those worms turn into calanders.

But whether this will be sufficient for the corn dealers, bakers, millers, and those who cannot see past the end of their nose, and from whom I have had to put up with so much contradiction concerning reproduction, I am still inclined to doubt.

  • 1687 October 17 (Letter L-193) to Members of the Royal Society

He found the origin of the maggots that grew into flies.

  • 1692 March 7 (Letter L-216) to Members of the Royal Society

I did, in the summer of the year 1690, request a corn-merchant to collect me a little box with wheat, in which the Wolf [corn-moth] was, in order, if it were possible, to convince those people who are taken in by a prejudice, namely that the Wolf is not produced by anything but a putrefaction, and as others say, by a mist, in what way the worm that is called the Wolf, propagates.

  • 1693 October 15 (Letter L-228) to Members of the Royal Society

Leeuwenhoek responded to Kircherus's Onderaartsche Werelt: "It has been found by research that Fleas also originate from piss, mixed with dust from the floor, as well as from their own excrements."

Now I entirely deny that fleas could be formed from dust and piss, and I assert that in my view this is impossible.

  • 1695 May 23 (Letter L-255) to Maarten Etienne van Velden

Leeuwenhoek asserted the impossibility of small flies being generated from the bodies of big dead caterpillars.

For every Creature must reproduce its own kind, except when two different Animals copulate, in which case a Creature is bound to be generated which resembles neither its Father nor its Mother

  • 1695 July 10 (Letter L-260) to Frederik Adriaan van Reede van Renswoude

To refute the origins of aphids in putrefaction, he described their life cycle.

  • 1695 July 12 (Letter L-261) to Maarten Etienne van Velden

Following up on his earlier letter to Van Velden, Leeuwenhoek described the role of caterpillars in the life cycle of butterflies and moths.

  • 1711 September 22 (Letter L-481) to Members of the Royal Society

To refute the origins of mites in putrefaction, he described their life cycle.

  • 1716 June 12 (Letter L-535) to Antony Cink:

Now when we view the admirable structure that is enclosed in a little grain of barley, shall we then continue to believe that any growth at all, however slight, can originate through putrefaction of the barley, even if a full load of barley lies piled up? And so I am also firmly convinced that from decay or putrefaction of any substance whatsoever not the tiniest living creature, or seed-bearing plant can spring forth, as several times has been said by me.