Darwin is not dead!

Well, actually, he is. Sorry if I got anybody's hopes up out there.

I claim he is living, because I am FINALLY returning to resume work on this blog, so thus his discoveries live on in the text that I type.

(Truthfully, it was a New Year's Resolution - there is no time like May 21st to finally start achieving the goals!)

It seems important to resume given the current issues facing our society - systemic issues of under-education about important concepts: climate change & global warming, evolution, vaccinations, and how these mis-informed beliefs can yield dangerous political, environmental, and social consequences.

Knowledge is our power to confront oppression and injustice.

So without further ado, here is an-under-10-minute-version of what evolution is:

Evolution of Populations

One common misconception about evolution is that individual organisms evolve. It is true that natural selection acts on individuals: each organisms' traits affect its survival and reproductive success compared with other individuals.

But the evolutionary impact of natural selection is only apparent in the changes in a population of organisms over time.

For example, the medium ground finch (Geospiza fortis), a seed-eater that lives on the Galapagos Islands.

 In 1977, the population of birds was decimated by drought; of some 1,200 birds, only 180 survived. During the drought, small soft seeds were in short supply. Thus, the members of the population with larger and deeper beaks were better adapted to eat the more plentiful (but more difficult to open) large hard seeds. These birds were the ones that survived the drought and went on to reproduce, so that the next generation of G. fortis had a larger beak than it had before the drought.

The period of drought is marked by a dramatic change
in body and beak size & shape

The finch population had evolved by natural selection.

 However, it is important to understand that the individual finches did not evolve.

Each bird had a specific size beak which did not change during the drought. Rather, the proportion of large beaks in the population increased from generation to generation: the population evolved, not its members.

By focusing on evolutionary change in populations, we can define evolution on its smallest scales, called microevolution, as changes in allele frequencies in a population over generations.







Natural selection is not the only cause of microevolution. There are three main mechanisms that cause allele frequencies to change:

1. Natural Selection
2. Genetic Drift
3. Gene Flow

Natural Selection

Individuals in a population exhibit variations in their heritable traits, and those with traits that are better suited to their environment tend to produce more offspring than those with traits that are not as well suited.

In genetic terms, the selection results in alleles being passed to the next generation in proportions that difer from those in the present generation.

For example, the fruit fly D. melanogaster has an allele that confers resistance to several insecticides, including DDT. This allele has a frequency of 0% in laboratory strains of fruit flies established from collected wild flies from the 1930s. 

However, in strains established from flies collected after 1960, the allele frequency is 37%. It can be inferred that this allele arose by mutation between 1930 and 1960 as a response to the use of DDT as insecticide in farming.

As this example shows, an allele that confers insecticide resistance will increase in frequency in a population exposed to that insecticide. Such changes are not coincidental. 

By consistently favoring some alleles over others, natural selection can cause adaptive evolution.

Genetic Drift

If you flip a coin 1,000 times, a result of 700 heads and 300 tails might make you suspicious about the coin.

But if you flip a coin only 10 times, and outcome of 7 heads and 3 tails would not be surprising. the smaller the number of coin flips, the more likely it is that chance alone will cause a deviation from the predicted result. 

Chance events can also cause allele frequencies to fluctuate unpredictable from one generation to the next, especially in small populations - a process called genetic drift.

Figure 1 models how genetic drift might affect a small population of wildflowers. In this example, an allele is lost form the gene pool, but it is a matter of chance which allele is lost. Such unpredictable changes in allele frequencies can be caused by chance events associated with survival and reproduction. 

figure 1

Perhaps a large animal, like a cow in a field grazing, stepped on the three C(w) C(w) individuals in generation 2, killing them and increasing the chance that only the C(r) allele would be passed to the next generation. 

Allele frequencies can also be affected by chance events that occur during fertilization. for example, suppose two individuals of genotype C(r)C(w) had a small number of offspring. By chance alone, every egg and sperm pair that generated offspring could happen to have carried the C(r) allele and not the C(w) allele. Certain circumstances can result in genetic drift having a significant impact on a population. There are two different examples of this: the founder effect and the bottleneck effect.

1.) The Founder Effect

When a few individuals become isolated from a larger population, this smaller group may establish a new population whose gene pool differs from the source population; this is called the founder effect.

The founder effect might occur, for example, when a few members of a population are blown by a storm to a new island. Genetic drift, in which chance events alter allele frequencies, will occur in such a case if the storm indiscriminately transports some individuals, but not others, from the source population.

This effect is probably responsible for the high frequency of inherited disorders among isolate human populations.

For example, in 1814, only fifteen British colonists founded a settlement on Tristan da Cunha, a group of islands in the Atlantic Ocean between Africa and South America.

One of the colonists apparently was carrying a recessive allele for retinitis pigmentosa, a type of progressive blindness that only afflicts homozygous individuals.

Of the founding colonists' 240 descendants, four had the blindness. In the present day, the frequency of retinitis pigmentosa is ten times higher on Tristan da Cunha than in the rest of the population on Earth.

2.) The Bottleneck Effect

A sudden change in the environment, such as a fire or flood, may drastically reduce the size of a population. A severe drop in population size can cause the bottleneck effect, so named because the population has passed through a "bottle-neck" that reduces its size.

By chance alone, certain alleles may be over-represented among the survivors, others may be underrepresented, and some may be absent altogether.

Ongoing genetic drift is likely to have substantial effects on the gene pool until the population becomes large enough that chance events have less impact.

But even a population that passes through a bottleneck eventually recovers its size, although it may have low levels of genetic variation for a long period of time - a legacy of the genetic drift that occurred when the population was small.

For example, the African Cheetah almost went extinct due to hunting for its exotic pelt. Radical protections were put in place and the population recovered, but because there were so few surviving individuals to begin re-establishing the population that the allele variations among the current population is very low.

Thus, if one Cheetah is susceptible to a certain disease, most likely all other members of the species are as well. Bottlenecks can have a lasting impact on the survivability of a species based on which alleles survived the event.

Summary

The examples discussed highlight four key points:

• Genetic drift is significant in small populations

• Genetic drift can cause allele frequencies to change at random

• Genetic drift can lead to a loss of genetic variation within populations

• Genetic drift can cause harmful alleles to become fixed

Gene Flow

Gene flow is the transfer of alleles into or out of a population due to the movement of fertile individuals or their gametes.

For example, suppose a hypothetical group of wildflowers on the top of a hill, all red ( C(r)C(r)) homozygous. 

At the bottom of the hill is a group of white wildflowers - C(w)C(w). 

A bee flies up the hill with pollen from the white flowers and introduces the C(w) allele to the red population. 

The introduction would modify the original population's gene frequencies in the next generation.

Because alleles are exchanged between populations, gene flow tends to reduce the genetic differences between populations. 

If it is extensive enough, gene flow can in fact result in two populations combining into a single population with a common gene pool.

Alleles transferred by gene flow can also affect how well populations are adapted to local environmental conditions.

For example, researchers, studying the songbird Parus major on the Dutch island of Vlieland observed survival differences between two populations on the island. 

Females born in the eastern population survived twice as well as females born in the central population, regardless of where the females eventually settled and raised offspring.

This finding suggests that females born in the eastern population are better adapted than females born in the central population.

However, extensive field studies proved that the two populations are interconnected with high levels of gene flow (mating), so there should be little genetic difference between them. 

Why then are eastern females better at surviving?

The answer lies in the unequal amounts of gene flow from the mainland. In a given year, 43% of the first-time breeders in the central population are immigrants from the mainland, compared with only 13% in the eastern population.

Birds with genotypes from the mainland apparently survive and reproduce poorly on Vlieland, and in the eastern population, selection reduces the frequency of these genotypes. 

But in the central population, gene flow from the mainland is so high that it overwhelms the effects of selection. 

As a result, females born in the central population have many immigrants genes, reducing their survivability. 

Gene flow can also transfer alleles that cause adaptive prowess.

For example, gene flow has resulted in the worldwide spread of several insecticide-resistance alleles in the mosquito Culex pipiens, a vector of West Nile virus and other diseases. 

Each of these alleles has a unique genetic signature that allowed researchers to document that it arose by mutation in one or a few geographic locations. In their population of origin, these alleles increased because they provided insecticide resistance. These alleles were then transferred to new populations, where again, their frequencies increased as a result of natural selection.

Finally, gene flow has become an increasingly important agent of evolutionary change in human populations. Humans today move much more freely about the world that in the past. As a result, mating is more common between members of populations that previously had little to no contact, leading to an exchange of alleles and fewer genetic differences between those populations.

Concluding Thoughts

I have discussed the different forms of microevolution: natural selection, genetic drift, and gene flow. It has been shown how these forces cause evolutionary change that results in new species.

The next post will discuss why Natural selection is the only mechanism that consistently causes adaptive evolution.

The Scientific Evidence Supporting Evolution

This post will discuss the variety of scientific evidence supporting evolution.

In the Origin of Species, Darwin marshaled a broad range of evidence to support the concept of descent with modification. Still - as he acknowledged - there were many instances where evidence was lacking.

Original Origin of Species

In the last 150 years, many new discoveries have filled the gaps that Darwin identified. Significantly, the Theory of Evolution has not been weakened but instead strengthened by the genetic revolution. The discovery of DNA has lent itself to more detailed understanding of how descent with modification has occurred.

Let's consider the types of evolutionary evidence:

• Fossil Record (including Transitional Fossils)  - Both discussed on other pages (see links)
• Direct observation of evolution - also see "Before Our Very Eyes"
• Homology
• Biogeography

And now, let's examine more closely three of the four below:

Direct Observations of Evolutionary Change

Biologists have documented observed evolutionary change in thousands of scientific studies. Let's take a look at two examples in particular.

Natural Selection in Response to Introduced Plant Species

Herbivores often have adaptations that help them feed efficiently on their primary food sources. What happens when herbivores begin to feed on a plant species with different characteristics than their usual food source?

Corizus hyoscyami

An opportunity to study this question in nature is provided by soapberry bugs, which use their hollow, needle-like mouth part to feed on seeds located within the fruits of various plants. In southern Florida, the soapberry bug Jadera haematoloma feeds on the seeds of a native plant, the balloon vine (Cardiospermum corindum). But in central Florida, balloon vines have become rare, so instead soapberry bugs in that region now feed on the goldenrain tree (Koelreuteria elegans), a species recently introduced from Asia.

Soapberry bugs feed most effectively when their beak length closely matches the depth at which the seeds are found within the fruit. Goldenrain tree fruit consists of three flat lobes, and its seeds are much closer to the fruit surface than the seeds of the plump, round native balloon vine. Predictably, the beak lengths of soapberry bugs living in central Florida are evolving to be shorter. 

goldenrain tree

Researchers have also studied beak length evolution in bug populations that feed on a variety of plants in Louisiana, Oklahoma, and Australia. IN these locations, the fruit of the newly introduced plants is larger than the native plant. Thus, these populations have evolved a longer beak length. Given enough time, the soapberry bugs may evolve into two distinct species, those with shorter beaks, and those with longer beaks.

The Evolution of Drug-Resistant Bacteria

An example of ongoing natural selection that dramatically affects humans is the evolution of drug-resistant pathogens. This is a particular problem with bacteria and viruses because resistant strains of these pathogens can proliferate very quickly.

For example, the evolution of drug resistance by the bacterium Staphylococcus aureus. About one in three people harbor this species in their skin or nasal passages with no negative effects. However, certain genetic varieties (strains) of this species known as methicillin-resistant S. aureus (MRSA) are dangerous pathogens. The past few decades have seen an alarming increase in virulent forms of MRSA such as clone USA300, a strain that can cause "flesh-eating diesase" and potentially fatal infections. How did this strain of MRSA become so dangerous?

MRSA

In 1943, when penicillin became the first widely antibiotic, S. aureus had already developed a 20% resistance to the drug. The bacteria had mutated and developed an enzyme that it could use to destroy the penicillin. Researchers responded and developed antibiotics that were resistant to the new enzyme, but some S. aureus populations developed resistance to each new drug within a few years.

In 1959, doctors began using the extremely powerful methicillin, but within two years, methicillin-resistant strains appeared. How did these strains emerge?

Methicillin works by deactivating a protein that bacteria use to synthesize their cell walls. However, S. aureus populations exhibited variations in how strongly their members were affected by the drug. In particular, some individuals were able to synthesize their cell walls using a different protein that was not affected by methicillin. These individuals survived the methicillin treatments and reproduced at higher rates. Over time, these resistant strains became increasingly common leading to the spread of MRSA.

Although initially MRSA could be controlled by antibiotics that worked differently than methicillin, it has become increasingly difficult because some MRSA strains are resistant to multiple antibiotics. This is presumably because bacteria can exchange genes with members of their own and other species.Thus, the current multi-drug resistant forms may have emerged over time as MRSA strains that were resistant to different antibiotics exchanged genes.

Understanding the Implications

These two examples highlight two key points about natural selection. First natural selection is not a process of editing, not a creative mechanism. A drug does not create resistant pathogens; it selects for resistant individuals that are already present in the population. Second, natural selection depends on time and place. It favors those characteristics in a genetically variable population that provide advantage in the current local environment. What is beneficial in one situation may be useless or even harmful in another. Beak lengths arise that match the size of the typical fruit eaten by a particular soapberry bug population. However, a beak length suitable and beneficial for fruit of one size can be a disadvantageous when the bug is feeding on fruit of another size.

Homology

Another type of evidence for evolution comes from analyzing similarities among different organisms. As discussed, evolution is a process of descent with modification: Characteristics present in an ancestral organism are altered (by natural selection) in its descendants over time as they face different environmental conditions. As a result, related species can have characteristics that have an underlying similarity yet function differently. Similarity resulting from common ancestry is known as homology.

Anatomical and Molecular Homologies

The view of evolution as a remodeling process leads to the prediction that closely related species should share similar features - and they do. Of course, closely related species share the features use to determine their relationship, but they also share many other features. Some of these shared features make little sense except in the context of evolution.

For example, the forelimbs of all mammals, including humans, cats, whales, bats, and many others, show the same arrangement of bones from the shoulder to the tips of the digits, even though these appendages have very different functions: lifting, walking, running, swimming, or flying. 

Such striking anatomical resemblances would be highly unlikely if these structures had arise anew in each species. Rather, the underlying skeletons of the arms, forelegs, flippers and wings of different mammals are homologous structures that represent variations on a structural theme that was present in their common ancestor.

Comparing early stages of development in different animal species reveals additional anatomical homologies not visible in adult organisms. 

For example, at some point in their development, all vertebrate embryos have a tail located posterior to the anus as well as structures called pharyngeal pouches (gills). 

These homologous throat pouches ultimately develop into structures with very different functions, such as gills in fishes and parts of the ears in humans and other mammals.

Perhaps the most interesting homologies concern the "left over" structures of marginal, if any importance to the organism. These vestigial structures are remnants of features that served a function in the organism's ancestors.

For example, the skeletons of some snakes retain vestiges of the pelvis and leg bones of walking ancestors. Another example is provided by eye remnants that are buried under the scales of blind species of cave fishes. We would not expect to see these vestigial structures if snakes and blind cave fishes had origins separate from other vertebrate animals, or if they had been created. 

Here are a few more examples of vestigial organs:

vestigial human appendix

Vestigial wisdom teeth

Blind mole rat has flaps of skin that seal its eyes

Vestigial pelvis in whales

Similarities among organisms can also be observed at the molecular level. All forms of life use the same genetic language of DNA and RNA, and the genetic code is essentially universal. thus it is likely that all species descended from a common ancestors that used this code. But molecular homologies go beyond a shared code. 

For example, organisms as dissimilar as humans and bacteria share genes inherited from a very, very distant common ancestor. Some of these homologous genes have acquired new functions, while others, such as those coding for the ribosomal subunits used in protein synthesis, have retained their original functions. It is also common for organisms to have genes that have lost their function even though the homologous genes in the related species may be fully functional.

 Like vestigial structures, is appears that such inactive vestigial genes may be present simply because a common ancestor had them.

Homologies and "Tree Thinking"

Some homologous characteristics, such as the genetic code, are shared by all species because they date to the deep ancestral past. In contrast, homologous characteristics that evolved more recently are shared only within smaller groups of organisms. 

Map of Biological Domains and Kingdoms

Consider the tetrapods, the vertebrate group that consists of amphibians, mammals, and reptiles. All tetrapods have limbs with digits, whereas other vertebrates do not. Thus, homologous characteristics form a nested pattern: All life shares the deepest layer, and each successive smaller group adds its own homologies to those it shares with larger groups. 

Example of Nesting

This nested pattern is exactly what we would expect to result from descent with modification from a common ancestor.

Convergent Evolution

Although organisms that are closely related share characteristics because of common descent, distantly related organisms can resemble one another for a different reasons: convergent evolution, the independent evolution of similar features in different lineages.

For example, marsupial mammals are distinct from another group of mammals the eutherians - few of which live in Australia. Eutherians complete their embryonic development in the uterus, whereas marsupials are born as embryos and complete their development in an external pouch.

Some Australian marsupials have eutherian look-alikes with superficially similar adaptations. For instance, a forest-dwellling Australian marsupial called the sugar glider is superficially very similar to flying squirrels, the gliding eutherians that live in the North American forests. But the sugar glider has many other characteristics that make it a marsupial, much more closely related to kangaroos and other marsupials than to flying squirrels or other eutherians. 

Once again, an understanding of evolution can explain these observations. although they evelved independently from different ancestors, these two mammals have adapted to similar environments in similar ways. 

Biogeography

Another type of evidence for evolution comes from biogeography, the geographic distribution of species. The distribution of organisms is influences by many factors, including continental drift, the slow movement of Earth's continents over time. 

About 250 million years ago, these movements united all of Earth's landmasses into a single large continent called Pangaea. Roughly 200 million years ago, Pangaea began to break apart; by 20 million years ago, the continents we know today were within a few hundred kilometers of their present locations.

We can use evolution and continental drift to predict where fossils of different groups of organisms might be found.

Horse Evolution

For example, scientists have constructed evolutionary trees for horses based on anatomical data. these trees and the ages of fossils of horse ancestors suggest that present-day horse species originated 5 million years ago in North America. At that time, North and South America were close to their present locations, but they were not yet connected, making it difficult for horses to travel between them. Thus, we would predict that the oldest horse fossils should be found only on the continent on which horses originated - North America. this prediction and others like it for various other groups have proven true, continuing to supply more evidence for evolution.

An understanding of evolution also helps understand biogeographic data. For example, islands generally have many species of plants and animals that are endemic (found nowhere else in the world) Yet as Darwin described in The Origin of Species, most island species are closely related to species from the nearest mainland or a neighboring island. He explained this observation by suggesting that islands are colonized by those same species. these colonists eventually give ries to new species as they adapt to their new environment. An example of this is currently occurring in the 35 year old Pan Mrcrau experiment.

Such a process also explains why two islands with similar environments in distant parts of the world tend to be populated not by species that are closely related to each other, but rather by species related to those of the nearest mainland, where the environment is often quite different.

Concluding Thoughts


Clearly, the pattern of evolution - the observation that life has evolved over time - has been documented directly and is supported by a great deal of evidence. In addition, Darwin's explanation of the process of evolution - that natural selection is the primary cause of the observed pattern of evolutionary change - helps to make sense of massive amounts of data. The effects  of natural selection can be observed and tested in nature.

The next blog post will contain information regarding micro evolution of populations and a discussion of the Hardy-Winberg equation.

The Darwinian Revolution

Aristotle

A Brief History Concerning Evolutionary Thought

Darwin's idea of descent with modification actually has deep historical roots.


Long before Darwin was born, many Greek philosophers suggested that life might have changed gradually over time.


But Aristotle viewed species as fixed, and his opinion influenced much of Western science.



During his observations of nature, Aristotle recognized certain affinities among organisms. He decided that life-forms might possibly be arranged on a type of ladder or scale of increasing complexity, later called scala naturae ("scale of nature"). Each life form is perfect and permanent and has an allotted rung on the ladder. (fig 1)

figure 1

Aristotle's ideas were mostly consistent with the Old Testament account of creation. In the 1700s, scientists would interpret the remarkable match of each organism to its specific environment as evidence of design and a creator, with each species having a specific purpose.

Linnaeus

Carolus Linnaeus, a Swedish physician and botanist who attempted to classify life's diversity, held this opinion and did his work "for the greater glory of God." Linnaeus developed the classification system binomial nomenclature that is still used today. In contrast to Aristotle's scala naturae, Linnaeus adopted a classification system where he grouped similar species into increasingly general categories.

Linnaeus did not attribute the resemblances among species to evolutionary kinship, but rather to the pattern of their creation.

Nearly a century later, Darwin argued that classification should be based instead on evolutionary relationships.




Why did Darwin suggest this?

Darwin drew from the work of scientists studying fossils in the new field of Paleontology, developed largely by French scientist Georges Curvier in the 1700-1800s. While examining the layers of the earth near Paris, Curvier noticed that the older the stratum of earth, the more dissimilar its fossils were to current life-forms. Additionally, he discovered that from one layer to the next, some new species appeared while other disappeared. He inferred that extinctions are probably a common occurrence in the history of life.

In 1795, Scottish geologist James Hutton proposed that Earth's geologic features could be explained by gradual mechanisms still operating today. For example, valleys may be formed by rivers wearing through rocks and sediment - such as the Grand Canyon.

How did all of this impact Darwin and his creation of evolutionary theory?

Darwin agreed that if geologic change results from slow, continuous actions rather than sudden events, then earth must be much, much older than the widely accepted age at the time of a few thousand years. He then reasoned that perhaps similarly slow and subtle processes could produce substantial biological change. Darwin was not the first to apply this idea of gradualism to evolution, however.

During the 18th century, multiple naturalists (including Darwin's grandfather, Erasmus Darwin) suggested that life changes in response to environmental change. But only one of Charles Darwin's predecessors proposed a mechanism for how life changes over time: French biologist Jean Baptiste de Lamarck.

In 1809, the year Charles Darwin was born, Lamarck published his hypothesis. He compared living species with fossil forms and found what appeared to be several lines of descent, each in a flawless chronological series of older to younger fossils culminating with a currently living species. He explained these findings using two principles that were widely accepted at the time:

• use and disuse; the idea that parts of the body that are used extensively become larger and stronger while those that are not used deteriorate (vestigial organs)

Examples:

pelvic bones in whales

gills in human and bird fetuses

the appendix in humans

• inheritance of acquired characteristics; an organism can pass these modifications along to its offspring (through what we now know is DNA - genetic code/instructions for life)

DNA

Darwin's Beginnings

Darwin was born in 1809 in England. As a boy, he had a consuming interest in nature. When not reading nature books, he was fishing, hunting, and collecting insects. Darwin's father, a physician, sent his son to medical school in Edinburgh. But Charles found medicine boring and surgery horrifying and transferred to Cambridge University, intending to become a clergyman.

While at Cambridge, Darwin became the protege of the Reverend John Henslow, a botany professor. After Darwin graduated, Henslow recommended him to Captain Robert FitzRoy, who was preparing the survey ship the HMS Beagle for a long voyage around the world.

The Voyage of the Beagle

In December 1831, Darwin embarked on the Beagle with the primary mission being a voyage to chart poorly known stretches of the South American coastline. While the crew surveyed the coast, Darwin spent most of his time on shore, observing and collecting thousands upon thousands of South American plants and animals. He noticed the characteristics of plants and animals that made them well suited to each diverse environment.

His most well-known work is his study of the finches of the islands he visited who trace their origins to South America. Further discussion of Darwin's finches will be covered in a later post.

Darwin's Focus on Adaptation

Darwin proposed the mechanism of natural selection to explain the observable patterns of evolution he found on his voyage. He related it to artificial selection, the process by which humans have sculpted crops, livestock, and pets so that the possess desired traits.

Examples of micro-evolution in artificial selection:

Dog breeding

artificially selected for different characteristics; produces different varieties and eventually species

Darwin argued that a similar process occurs in nature. He based this argument on two observations, from which he then drew two inferences.

Observation #1: Members of a population often vary in their inherited traits

variety of beetle phenotypes

Observation #2: all species can produce more offspring than their environment can support, and many of these offspring fail to survive and reproduce.

the weakest do not survive

Inference #1: Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals.

well-adapted animals produce many offspring

Inference #2: This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over many generations.

Blue-footed Boobies breed for the bluest feet

Darwin saw an important connection between natural selection and the capacity of organisms to "overproduce". He made the connection after reading an essay by economist Thoma Malthus, who argued that much of human suffering - disease, famine, war - was the inescapable consequences of the human populations's potential to increase faster than food supplies and other resources. Darwin realized that the capacity to overreproduce was a characteristic of all species. Of all the many eggs laid and young born, only a tiny fraction complete their development to leave offspring of their own.

the evolution of the modern horse by natural selection

An organisms' heritable traits influence not only its own performance, but also how well its offspring can cope with environmental challenges. For example, an organism might be faster due to a trait that then gives it an advantage at escaping predators. That organism is more likely to survive to adulthood and reproduce to produce more organisms that run faster, and so on and so forth.



How rapidly can these changes occur? Darwin reasoned that if artificial selection can bring about dramatic change in a relatively short period of time, then natural selection should be capable of substantial modification of species over many hundreds of generations Even if the advantages of the traits are very slight, the variations will gradually accumulate and compound, and less favorable variations will diminish over time this process will increase the frequency of individuals with favorable adaptations and hence refine the match between organisms and their environment.


In the next blog entry, the direct observations of evolutionary change will be discussed.

Endless Forms Most Beautiful: An Introduction to Evolution

Along the coastal portion of the Namib desert in southwestern Africa, lives a beetle, Onymacris unguicularis. In this harsh climate, unguicularis must stand on its head to obtain water from fog blowing across the dunes. Small drops of moisture collect on the beetle's abdomen and run down into its mouth from this position.

This interesting evolutionary adaptation is merely one example of the brilliance of nature and the ability of species to adapt to survive even in extreme environments. It shows the diversity that results from the variety of climates that exist on the planet. The "headstander" beetle is in fact a member of an amazingly diverse group - over 350,000 types of beetle. Beetles actually account for 1 in every 5 known species. All of these beetles share similar features; three pairs of legs, two pairs of wings, and a hard exoskeleton. But they also differ from one another.

The headstander beetle and its relatives illustrate three key observations about life:

• the radical ways in which organisms are suited directly to their individual environments
• the unity of life (many shared characteristics)
• the diversity of life (millions of species, for example, of insects)

Over one hundred and fifty years ago, Charles Darwin wrote a hypothesis for these three broad observations. He first published his ideas in his book The Origin of Species. This sparked a revolution in evolutionary biology, and a quest by all scientists across disciplines to either bolster or reject this radical hypothesis.

What ensued was a massive accumulation of evidence for the process of evolution, and no evidence contradicting it. 

Darwin's original hypothesis has now graduated into the ranks of scientific theory, surrounded by others such as the Theory of Gravity, Heliocentric Theory, and The Germ Theory of Disease.

It is essential the evolution be understood, because it continues to have an impact on our lives; the food we eat (GMOs), our rapidly changing climate (whether from planetary forces or human causation), and our health (with the use of pharmaceuticals and drug-resistant bacteria). Evolution is critical to modern medicine, chemistry, physics, and of course biology.

It is the purpose of this blog to fully educate on exactly what evolution is and what it isn't.

To set the stage, the next post will discuss Darwin's lifelong quest to explain the adaptations, unity and diversity of what he called life's "endless forms most beautiful."