[Taxacom] University of Cambridge evoutionary biogeography stuck in 1859

[John Grehan]

If the university of Cambridge is to believed, the key to understanding
evolutionary biogeography (i.e. the origin of allopatry) is reduced down to
a couple of simplistic experiments. As for Darwin, and indeed the great
majority of biogeographers, the existence of distributions as the test of
such notions does not exist. Geography is a stage, not a process.

https://www.darwinproject.ac.uk/learning/universities/getting-know-darwins-science/biogeography

*Observations aboard the Beagle*

During his five year journey around the world on *HMS Beagle*
<https://www.darwinproject.ac.uk/geology-beagle-voyage>, Charles Darwin
encountered many different landscapes and an enormous variety of flora and
fauna. Some of his most vivid experiences were on the islands of the coast
of South America, including the now-famous Galapagos archipelago. Darwin
was fascinated by the geographic relationship between the South American
coast and its nearby islands; he puzzled over why plants and animals on
nearby islands were similar to those on the mainland. Darwin was not
satisfied by the traditional explanation provided by many naturalists of
his day (including the famous Harvard naturalist Louis Agassiz
<http://www.darwinproject.ac.uk/namedef-43>), that each organism was
specially created for its geographic location. After his return from the
*Beagle*, he started to challenge the tenets of special creation theory.
Eventually, Darwin suggested that species were transported from the
mainland to the islands, where they continued to evolve.

*Seeds in salt water*

For his theory to work, Darwin had to prove that it was possible for
mainland species to be transported across oceans and to survive on nearby
islands. In the 1850s he embarked on a series of experiments to demonstrate
that a variety of cross-oceanic dispersal methods were possible. He
conducted several experiments to test whether the seeds of common garden
plants could be soaked in salt water, survive, and germinate. Many of
Darwin's seeds survived this salt-water test, which suggested to Darwin
that his theory of seed dispersal and subsequent evolution was plausible.
Darwin also hypothesized that snails could be transported from mainlands to
islands via birds. To test this theory Darwin tested whether pond snails
would adhere to ducks' feet that were dangled into ponds. Although these
experiments were simple, the results gave Darwin substantial evidence for
the role of evolution in the history and distribution of life on earth.
*EXPERIMENT*

Recreate Charles Darwin's seeds in salt-water experiment!

What you will need:

   - 5 different kinds of seeds. Our recommendations: common oats, corn,
   broccoli, radishes, falx seeds, spinach, common peas, capsicum and lettuce.
   These seed varieties were used by Darwin. Most of these seeds can be
   obtained from a neighborhood hardware store or seed catalogue.
   - small vials of salt water. Average salt content of sea water is 3%,
   but you can expand this lesson by varying the concentrations in the vials,
   and testing those as well
   - small pots to plant the seeds in

How to set up:

   - Have the class break up into several groups
   - Give one type of seed to each group
   - Have each group describe its seeds: colour, texture, size, etc. Have
   each group make predictions about how the salt water will affect the seeds.
   Have a class discussion about these predictions.
   - Place the seeds in small vials filled with salt water. Leave them for
   a week and have the students make observations at regular intervals
   - Plant the seeds in compost after one week. Have the students observe
   the planted seeds at regular intervals for 2 weeks. At the end of the 2
   weeks, have your students record the total number of seeds that germinated

Results and Discussion:

   - Have each group share the total number of seeds that germinated
   - Discuss why certain seeds might have germinated more than others
   - Have the students reflect on their initial predictions
   - Discuss why this experiment was significant for Darwin. Make the point
   that experiments in the present can provide empirical suggestions for
   events in the past

Here is an example of how this activity was performed at Harvard:

While studying biogeography, the class conducted two experiments that
provided first-hand knowledge of Darwin’s work. The first experiment
mimicked Darwin’s 1855 work on seeds and salt-water. The experiment is
delightfully simple: each student took four jars, filled them with salt
water, added one species of seed to each jar, and labelled the jars with
the seed type. The students then left the seeds in their jars for four
weeks. At the end of these four weeks, the students rinsed off their seeds
and planted them in soil with labels to indicate where they had planted
each species. Each week the class met, the students were able to check on
their seeds to see whether the plants had germinated. The results aligned
very well with Charles Darwin’s: those seeds that he had found to sprout
also sprouted, while those seeds that didn’t germinate in Darwin’s
experiment also failed to germinate in our own time. This experiment is a
beautifully simple illustration of biogeography: many seeds survive weeks
in salt-water and are still capable of germinating. Darwin saw this
experiment as an explanation of the means by which plants appear in
disparate locales.

The other experiment the class conducted also investigated the method by
which species appear in different geographic locations. To conduct this
experiment, each student was given a duck’s foot, string, and had access to
a pond. The ducks’ feet were obtained from a local butcher. Each student
tied a string around their duck’s foot and dangled it into the pond. The
class left the feet in the pond for two hours. After two hours, each
student should pull their duck’s foot out of the pond and see if any living
creatures have attached to it. This experiment demonstrates the manner in
which specimens can be transported by birds across both water and land.