evolution – Page 3 – Montessori Muddle

Evolution in Action

A fascinating study of 56,000 generations of bacteria, in 12 different populations, carefully documents how a new ability evolved in one of the populations — the ability to use citrate for food in addition to glucose.

About the key step in the process:

“It wasn’t a typical mutation at all, where just one base-pair, one letter, in the genome is changed,” he said. “Instead, part of the genome was copied so that two chunks of DNA were stitched together in a new way. One chunk encoded a protein to get citrate [for food] into the cell, and the other chunk caused that protein to be expressed.”

— Evolution is as complicated as 1-2-3 from Michigan State University.

That was the second step in a three step process:

The first stage was potentiation, when the E. coli accumulated at least two mutations that set the stage for later events. The second step, actualization, is when the bacteria first began eating citrate, but only just barely nibbling at it. The final stage, refinement, involved mutations that greatly improved the initially weak function. This allowed the citrate eaters to wolf down their new food source and to become dominant in the population.

Note

I’ve been discussing different genres of scientific writing with my middle school class, so it’s interesting to point out that the article this post refers to is just a press release about the actual research paper. These are two very distinct types of scientific writing.

On the Origin of Species

Perhaps the key reason for the profound influence of Darwin’s “On the Origin of Species” is that it’s such a well written and well reasoned argument based on years of study. It is a wonderful example of how science should be done, and how it should be presented. In the past I’ve had my middle schoolers try to translate sections of Darwin’s writing into plainer, more modern English, with some very good results. They pick up a lot of vocabulary, and are introduced to longer, more complex sentences that are, however, clearly written.

Diagram and notes on the bird species P.Nanus from The Zoology of the Voyage of H.M.S. Beagle, Part 3: Birds by J. Gould and G.R. Gray (edited by C.Darwin). Image via Darwin Online.

The text of “On the Origin of Species” is available for free from the Gutenberg library. Images of the original document can be found (also for free) at the UK website, Darwin Online (which also includes the Darwin’s annotated copy). Darwin Online also hosts lot of Darwin’s other works, as well as notes of the other scientists on The Beagle, among which is included some wonderful scientific diagrams.

This year, I’m going to have the middle schoolers read the introduction, while the honors environmental science students will read selected chapters and present to the class — this will be their off-block assignment.

Cofsyphus_Darwini — Diagram of the fish Cofsyphus Darwini by L. Jenyns in The Zoology of the Voyage of H.M.S. Beagle, Part 4: Fish (edited by C.Darwin). Image via Darwin Online.. .

A Darwinian Debt

Evidence is mounting that fish populations won’t necessarily recover even if overfishing stops. Fishing may be such a powerful evolutionary force that we are running up a Darwinian debt for future generations.

— Loder (2006), Point of No Return in Conservation in Practice.

Darwinian Debt. That’s the elegant phrase Natasha Loder (2006) uses to describe the observation that human pressure on the environment — fishing in this particular example — has forced evolutionary changes that are not soon reversed.

Fishermen prefer to catch larger fish, depleting the population of older fish, and allowing smaller fish to successfully reproduce. Over a period of years this artificial selection — as opposed to natural selection — gives rise to new generations of fish that are permanently smaller than they used to be. And the fisheries find it hard to recover even after decades (Swain, 2007):

Populations where large fish were selectively harvested (as in most fisheries) displayed substantial declines in fecundity, egg volume, larval size at hatch, larval viability, larval growth rates, food consumption rate and conversion efficiency, vertebral number, and willingness to forage. These genetically based changes in numerous traits generally reduce the capacity for population recovery.

— Walsh et al., 2005, Maladaptive changes in multiple traits caused by fishing: impediments to population recovery in Ecology Letters.

Epigenetics: How our Environment Affects what our Genes Do.

The middle-school introduction to genetics tends to start with Mendel‘s pea experiments and end with Punnet Squares. The focus is on dominant and recessive genes and what’s expressed given various combinations.

However, the way genes behave are not quite that simple. Tim Spector’s new book, Identically Different, goes into the ways that people’s behavior and environment — the things they eat; the chemicals that surround them — affect the way their genes behave. Even identical twins can be profoundly different depending on things that happen in the womb.

Perhaps the most intriguingly argument is that the behavior of grandparents can affect their grandchildren. In the post World War II period in Britain food was scarce, and some people tended to episodes of starvation alternating with binge eating. Spector links this to an increase in the obesity of their grandkids.

The idea that your behavior can affect the expression of your kids’ genes is more akin to Lamark’s view of evolution than Darwin’s.

↬ The Dish ↬ BrianAppleyard,com.

DarwinTunes: Watching Music Evolve

Take randomly generated sound waves (using sine curves for example), mix them together to get beats, and then let people decide which ones sound best. Let the best ones mate — add in small mutations — and wait a few thousand generations for the sound patterns to evolve into music.

That’s what DarwinTunes does, and they let you participate in the artificial selection process (artificial as opposed to natural selection).

The details are included in their article: Evolution of music by public choice by MacCallum et al. (2012).

Humans Beings, Super-Predators

Usually, when new, more powerful predators evolve or come in from elsewhere, the local species can often adapt by themselves becoming better defended through a variety of means [larger sizes, thicker shells for example]; but this option seems to be closed when it comes to the evolution of humans as super-predators.

— Geerat Vermeij (2012), quoted in Walker (2012): Super-predatory humans on the BBC website.

Humans, using ingenuity and tools, have become an uniquely, irresistible predator species that the world has never seen before, and to which other species are finding it very difficult to adapt. That’s the premise of a paper by Geerat Vermeij that’s nicely summarized by Matt Walker on the BBC website.

Normally, predators and prey evolve and adapt to each other. Lions are better able to attack and kill smaller buffalo, which means the larger buffalo are more likely to survive, which results, over time, in the average size of the buffalo herds getting larger.

Humans, on the other hand, like to target the larger buffalo, creating a selective pressure the other way. Unfortunately, once the larger specimens are gone, humans will go after the smaller ones, and the intensity of the attacks have often been enough to drive entire species into extinction.

Though humans have been around for a couple hundred thousand years, we still have not seen our full impact on the environment. Which is somewhat interesting to consider.

Human Evolution: A Family Tree

The Smithsonian has an excellent, interactive, family tree for humanity that goes back 6 million years.

io9 has a neat image of key primate and homonid skulls that show the story of human evolution, and how we know about it.

Selective breeding of foxes

Silberfuchs_06 — A silver fox. Image by Zefram via Wikimedia Commons.

Evan Ratliff has an excellent article that ties well into our discussions of evolution. It’s on the breeding of foxes to make them want human companionship, much the same way wolves were domesticated.

… researchers … gathered up 130 foxes from fur farms. They then began breeding them with the goal of re-creating the evolution of wolves into dogs, a transformation that began more than 15,000 years ago.

— Ratliff (2011), in National Geographic, Taming the Wild

domestication-pigs — Wild boar (top) versus a domesticated pig (bottom). Note the floppier ears, a trait common to domesticated animals. Figure from Darwin (1968).

It worked remarkably well, and not just with foxes, but with rats and mink as well.

The scientist in charge, Dmitry Belyaev, was looking into something that Darwin observed in 1868: domesticated animals are smaller, with floppier ears and curlier tails, than their untamed ancestors.

In terms that we’ve studied, domesticated animals all have similar physical characteristics (phenotype) and Belyaev wanted to find the genotype. His theory is that there is:

… a collection of genes that conferred a propensity to tameness—a genotype that the foxes perhaps shared with any species that could be domesticated.

— Ratliff (2011), in National Geographic, Taming the Wild