Evolution is a Fact #28 - Something Darwin Didn't Say

cofty

One of my friends posted an inspirational picture on Facebook this morning. Even before I checked I knew that it was a fictional quote. It was written by somebody who has not grasped a basic fact about evolution.

Darwin Did Not Say This...

It is a common misunderstanding that evolution favours individuals who are able to adapt to their environment. This is simply not true. Individuals are either suited to the challenges of their environment or they die.

Evolution is something that happens to populations not to individuals.

To put it more technically, evolution is about the change in frequency of alleles (alternative versions of a gene) in a gene-pool.

This is nicely illustrated by a seven year field study of the predation of feral pigeon's that was conducted by Alberto Palleroni and his team of Harvard University.

They tagged 5,235 pigeons around Davis, California and observed 1,485 attacks by five adult peregrines over the period of their research. They noted which of six plumage types the pigeon displayed and whether the attack was successful.

The data showed that one plumage type, that was shared by 20% of the population, accounted for only 2% of all the falcon's kills. These lucky pigeons were the group that had a white rump. When a peregrine chooses its target it visually locks onto a victim and goes into a dive that can reach speeds up to 200 mph. The pigeons respond by dipping a wing and going into a roll. It seems that the flashing white patch makes it almost impossible for the falcon to track his prey.

The researchers tested their hypothesis by capturing 756 pigeons and switching tail feathers. They removed white feathers from the favoured pigeons and glued them onto the blue-barred pigeons. Having released the birds and observed their fate they discovered that the capture rates were reversed as expected.

During the seven years of the study Palleroni noted a steady rise in the percentage of white-rumped pigeons in the local population. The population of pigeons were evolving in response to the strong selection pressure of fast and hungry peregrines.

The important point to note is that no individual pigeon "adapted" to their environment. The ones that lacked the white patch got eaten if they were targeted by a falcon. 20% of pigeons were simply fortunate enough to possess a slight quirk in their genome that caused some of their feathers to be white rather than blue. These individuals leave slightly more offspring each season than pigeons who lack the gene for a patch of white feathers so that over a number of year the population of pigeons evolve.

Biologists have developed formulae to calculate the power of natural selection. Let's take a theoretical population of 1,000 individuals. Eight of them possess a trait that confers an advantage such that they leave 110 offspring compared to 100 from from those who don't. The advantageous trait will spread to 90% of the population in just 300 generations.

It is worth remembering that "fitness" is relative to the specific environment of a population. Suppose a new predator arrives who is not distracted by the white feathers - in fact he is attracted by it - then the pigeons who lack the white rump will be "more fit" and their presence will increase in the gene pool.

Evolution is a Fact - Index #1-20
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Evolution is a Fact #21 - Footprints in the Sand
Footprints at Laetoli show our Australopithecus afarensis ancestors were bipedal 3.6 million years ago.

Evolution is a Fact #22 - The Hillocks of Hiss
A vestigial feature if the human ear shared by 10% of the population demonstrates our evolutionary history.

Evolution is a Fact #23 - Faunal Succession
The consistent sequence of fossils found in the rocks can only be explained by evolution.

Evolution is a Fact #24 - The Origin of Your Inner Ear
How the bones that reptiles eat with became the bones that we hear with.

Evolution is a Fact #25 - Deep Time
Scottish geologist Andrew Hutton discovered the proof of earth's great antiquity.

Evolution is a Fact #26 - Colour Vision
How gene duplication - new "information" -and mutation equipped us with trichromatic vision.

Evolution is a Fact #27 - Monkeys, Typewriters, Shakespeare, 747s etc.
Evolution is a combination of random mutations and non-random selection.

slimboyfat

It is a common misunderstanding that evolution favours individuals who are able to adapt to their environment.

Is it? Many plants and animals are able to adapt to their environment and it is a selective advantage for them.

http://www.eeb.cornell.edu/agrawal/pdfs/whitman-and-agrawal-2009-Ch_1-Phenotypic-Plasticity-of-Insects.pdf

Phenotypic plasticity, through its ecological effects, can facilitate evolutionary change and speciation. Plasticity is important because it is an encompassing model to understand life on earth, it can increase fitness, generate novelity, and facilitate evolution, it structures ecological communities, and it has numerous practical applications.

DATA-DOG

I get it, I think. When a scientist speaks of fitness, he or she does not mean how many push-ups I can do, but whether or not I am fit for my environmental demands at a crucial moment, like predation.

My enviromental demands require that I work very hard. If I couldn't meet those demands because of physical limitations, I would have to seek other employment; in the distant past, that may have equated to death with no opportunity to pass on my genes.

Doctors have told me that I have the constitution of a Mack truck, so my ancestors must have been pretty tough and so were yours. Otherwise, we wouldn't be here. Our ancestors were fit for survival.

Let's say there was a major natural disaster and only those who were actually physically fit were going to survive, because survival required 14hrs running/work to escape the danger; would "fitness" then be considered "fitness"?? On the other hand, if something happened and I had to do a lot of math in my head or die..... no D-dog babies. 😔

DD

Ruby456

Patrick Bateson also discusses phentoypic plasticity and its implications

cofty

Data-Dog - Yes that's right.

Remember too that it's not all-or-nothing. If a genetic variation results in just 1 extra viable offspring per 100, then 90% of the population will share that gene within 3,000 generations.

All the other individuals will still be breeding successfully. In any given generation it would likely be impossible to detect the slight advantage by observation but the maths of natural selection is quietly doing its stuff.

SBF - Did you read the paper you posted a link to? If you did you would see the difference between phenotypic plasticity, which involves no change in the genome, and evolution which does. Shall I explain further?

Phenotypic plasticity is amazing - perhaps I will do a thread on it.

Clearview

Another awesome thread, thanks cofty :)

slimboyfat

Ruby evolution seems to be a much more complicated and multifaceted phenomenon than many popular accounts present. I really enjoyed Dawkins' The Blind Watchmaker and it was easy to understand especially for someone whose only exposure had been the blue Creation book. However it seems that Dawkins' tendency for reductionism results in a limited view of evolution focussing on selection at the level of genes. This necessarily involves excluding the role of adaption to environment and selection at different levels including group selection. Just as in a broader philosophical sense Dawkins also seeks to reduce reality to physical matter and nothing else. But reality rather appears to be, as Raymond Tallis says, irreducibly relational. Selection cannot be reduced to a single driving factor, and reality is a complex interaction of the physical and conscious experience. So it's interesting that it's his same tendency for reductionism that produces a view of evolution that has been criticised by evolutionary biologists such as Stephen Jay Gould as myopic that also produces Dawkins' strident materialism and atheism.

Yes Cofty in particular the following section that begins:

How Phenotypic Plasticity Contributes to Speciation
A remarkable claim is that phenotypic plasticity stimulates evolution and contributes to speciation. But how can environment-induced changes to the phenotypes of individuals influence evolution? Isn’t this Lamarckian, the assimilation of environmentally acquired traits into the genome? Surprisingly, phenotypic plasticity theory suggests that environment- induced changes to individuals can become absorbed into the genome (Jablonka et al. 1998, ten Cate 2000), but via traditional Medelian processes (West-Eberhard 2003, Schlichting 2004, Pigliucci et al. 2006). There are different hypothetical pathways for this to occur (e.g., Grether 2005, Rodríguez et al. 2007), but one possible pathway would be the following...

Ruby456

yup - I agree cofty's threads are pretty awesome - they make a person think

cofty

SBF - Did you read the paper you posted a link to? If you did you would see the difference between phenotypic plasticity, which involves no change in the genome, and evolution which does. Shall I explain further?

I don't think the paper is arguing that the genome needs to change cofty, But that what we thought of as noise, plasticity of phenotype, can feed back into the genome and stimulate parts that were perhaps seemingly idle (where is that good beer ad when you need it) we don't use most of it anyway. In other words it may be as sbf highlights above in the emboldened bit ...

sbf please correct me if I am wrong

I think the paper needs to be read at least four times

cofty

SBF & Ruby thank you for your input regarding phenotypic plasticity.

Life never fails to amaze.

The main point of the OP still stands as a corrective to a common misunderstanding - the ingenuity of some insects notwithstanding.

Evolution is something that happens across generations to local populations. Random mutations that contribute to an individual's "fitness" spread through the species with surprising speed.

shepherdless

Further to what Ruby says, if SBF (in his second post) is suggesting that phenotypic plasticity involves a change to a genome, I disagree. When read carefully and in context, particularly the next page, the paper doesn't say that at all.

Otherwise it appears to me Cofty and SBF are a little at cross purposes.

Anyway, an interesting yet complicated subject. I had not read about phenotypic plasticity before today.

Evolution is a Fact #28 - Something Darwin Didn't Say

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