There are almost as many ways to approach problems scientifically as there are problems. One consistent element, however, is a clear and concise statement of your hypothesis. Articulating a hypothesis as concisely and precisely as possible often sheds light on how you might make the observations or collect the necessary data to test it. This step can help you take a big idea or issue and break it down to a more manageable, answerable question. For example, let’s consider a problem that conservation biologists wonder (and worry) about: the impacts of human activities on plant populations.
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What’s an example of an overly broad research question?
Can humans unwittingly cause evolutionary changes in plants just by making use of them? Researchers addressed this big question with a simple but powerful investigation of a medicinal plant, the Tibetan snow lotus, Saussurea laniceps—a rare plant that lives in rocky habitats high in the eastern Himalayas.
In traditional Chinese and Tibetan medicine, snow lotus flowers are used to treat headaches and high blood pressure. The flowers are also valued as souvenirs. As a consequence, snow lotus flowers are highly sought after. But they’re not picked at random: larger flowers (found on taller plants), which are believed to be more potent, are strongly preferred by the human harvesters. It’s this fact that made it possible for the researchers to tackle the research question noted above.
What’s a more manageable version of the research question?
Is human harvesting of the snow lotus causing evolutionary change to the plants?
How might we recast the question as a testable hypothesis?
Because humans like to pick the tallest of the wild-
Human harvesting of the tallest snow lotus plants is causing the evolution of smaller plants.
How could the researchers determine whether the plants are becoming shorter over time?
This was their first step: they simply measured the snow lotus plants from recent collections sold in China.
Is there a “control group” with which to compare today’s plants?
Here’s where the researchers got clever. They came up with two different, but equally valuable, control groups. For the first, they headed to herbaria. These are the repositories of specimens acquired by explorers and collectors that serve as a tool for cataloging plant biodiversity around the world. The researchers measured snow lotus plants from eight herbaria and from numerous field collections, noting the date that each plant had been collected. What did their comparison reveal?
Prior to 1920, the average snow lotus plant height was 22 cm; the average snow lotus plant height collected after 2000 was just 14 cm. Without question, the more recently the plant had been collected, the smaller it was. (When they statistically evaluated the relationship between the year of collection and the plant height, they found a significant negative correlation: r2 = 0.44; p < 0.0001; N = 218.) From these collections, the researchers also measured snow lotus plants from a closely related species that is not generally picked. Over the course of 120 years, there was no decline in the average plant height for this relative. Snow lotus plants are getting smaller only for the species that is harvested by humans.
Could another comparison be made?
To further test their hypothesis, the researchers were able to make another, possibly even better, comparison. They compared the snow lotus size at a heavily harvested site with plants growing in protected, sacred Tibetan areas, where flower harvesting is not permitted. Here’s what they found:
| Protected Areas | Heavily Harvested Areas | |
|---|---|---|
| Plant height (average ± SE) | 22.7 ± 2.0 cm | 13.4 ± 0.4 cm |
The plants were about 40% shorter in the heavily harvested sites than in the protected areas!
Did the researchers prove their point? And does it matter?
The evidence strongly supports the researchers’ hypothesis. Humans have inadvertently imposed directional selection on the snow lotus. The researchers noted, too, that the intensity of the selection seems to have increased since the 1970s, as better roads have increased access to the habitat of the snow lotus and greater interest in alternative medicines has created a larger market for them.
Because smaller snow lotus plants produce fewer seeds, the fitness of the heavily harvested populations may be reduced. If this is the case, the conservation status of the plant may be threatened. Moreover, the case of the snow lotus may be just one example. If the phenomenon of humans unconsciously acting as a selective force when harvesting desirable species is more general, the implications for the conservation of species could be great.
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Can you think of other naturally occurring species that humans value and may harvest in ways that lead to inadvertent evolution?
Humans value the Tibetan snow lotus flower for medicinal and other purposes. Because people prefer to harvest the largest snow lotus plants, there has been selection for smaller plants. Data from herbaria collections and from snow lotus populations in protected areas reveal a significant negative trend in height over the past hundred years.
Explain the process used by scientists to investigate the research question: “Is human harvesting of the snow lotus causing evolutionary change to the plants?”