Ernst Mayr, Biologist Extraordinaire
An appreciation of Harvard's visionary of modern evolutionary synthesis
Nature Not Books
Like Darwin, Mayr was always fascinated by live animals in nature.
He was particularly compelled by the question: How do species
originate? Some three years before he died, he told me about his
delight when the University of Berlin called him back to celebrate
the 75th anniversary of receipt of his doctorate degree. I asked him
if I might accompany him to attend the scientific program. "Oh,
you don't want to do that," he remarked. "There will be no
science, just endless and boring talks by administrators."
We had been discussing modes of speciation, and I had shown him our
10-minute film on Mixotricha paradoxa, an Australian
termite protist, in his daughter Susanne Harrison's kitchen in
Bedford. I had explained "symbiogenesis" as a mode of
speciation. "I get it, I get it," he said, first
pensively, then excitedly as he watched the five or more integrated
microbial symbionts that comprise a single Mixotricha
protist swim away as a single individual.
I tried to distinguish "symbiosis" from
"symbiogenesis" for him. "Oh, you don't have to tell
me what 'symbiosis' is!" he exclaimed, a little impatiently.
"I studied symbiosis with Paul Buchner in Greifswald, who was a
young instructor there" for a very short time before he moved
on, eventually to Italy. Buchner, author of the seminal work
Endosymbiose der Tiere mit pflanzlichen Mikroorganismen
(1953), was the founder of modern symbiosis research.
Mayr took seriously Louis Agassiz's admonition. He studied
"Nature not Books" between 1928 and 1930 when he collected
more than 3,000 birds in the South Pacific, mainly the Solomon
Islands and New Guinea. He learned to live off the land. After
removal of the skin and feathers in the preparation of "study
skins" and taxidermic samples for species identification,
morphological analysis and shipment to museum collections, nothing
would be wasted: The innards went to pot for dinner. That Ernst Mayr
ate more birds of paradise than any other modern ornithologist is a
Mayr's work in the field, especially with avian diversity, led him
to his most familiar contribution to science, documented in his two
dozen single-authored or edited books and more than 600 scientific
publications. He framed the animal species concept. Members of the
same species can mate and breed to produce fertile offspring. Even
plants and animals that greatly resemble each other are not to be
assigned to the same species if they are not interfertile. On the
other hand, animals that look very different from each other (such
as Great Danes and Yorkshire terriers) if they produce fertile
offspring do belong to the same species.
He told me about the wood duck and the green-headed mallards
illustrated on his conservation-society shower curtain—that
they were perfectly fertile, and a mating between these birds
resulted in normal numbers of healthy chicks. He said that
nevertheless he agreed that the two very different-looking ducks
must be assigned, as they are, to two different species. Why?
Because, he insisted, even when they live on the same pond, such as
the duck pond here in Amherst, they only mate with their own kind.
His definition of species, he insisted, is "organisms are
members of the same species that, in nature, mate to
produce fertile offspring."
He always emphasized the importance of the environment. Speciation
could almost always be associated with geographical isolation. When
members of the same species are separated for long times by
environmental barriers (such as newly formed volcanic mountains,
islands, rivers or climatic change), the barriers lead to impeded
mating. It is these isolated populations that tend to form new
species. The importance of geographical details in the origin and
evolution of species was always emphasized. "I don't need to
measure the pH and see that it is lower than six in that
soil," he would say. "When sphagnum and cranberries grow
in the bog there, we know what the pH must be." A
proud naturalist, Mayr was a superb writer who communicated
primarily by handwritten notes. He was the last of the
neo-Darwinians to revere nature, work inside her and with her. His
life always extended beyond the computer and mathematical models.