First Essay: Human Evolution

There was a time not so long ago that people believed that evolution occurred through a “scala natura” a sort of staircase that showed the superiority of species. This staircase in actual was essentially the food chain and humans were placed at the top of this staircase, and considered the “fully evolved organism” of the animal kingdom. Another common misconception was that mankind along with all other life forms were created by a higher being and this higher being dictated how we looked, thought, evolved, and acted. Both these beliefs however were very wrong. As time passed new individuals arrived onto the scientific scene and brought with them an array of knowledge which would transform the way everyone viewed evolution.

”What is natural selection, and which individuals are the most “fit” in any species, including our own?”

First off natural selection is a term that was coined by a man named Charles Darwin (1809-1882). Darwin was a man obsessed with finding out the answer as to why some species could have such different and astounding traits than their cousins in different locations. On his voyage on the H.M.S Beagle Darwin was able to study and test several of his ideas which lead to the publication of his book entitled; “On the Origin of Species by Means of Natural Selection”. During this time Darwin created three postulates that summed up the process of natural selection:

• The ability of a population to expand is infinite, but the ability of any environment to support populations is always finite.
• Organisms within populations vary, and this variation affects the ability of individuals to survive and reproduce.
• The variations are transmitted from parents to offspring.

In any species there is a wide variety of differences that make each creature unique. These differences are the creature’s (or if you prefer organism’s) ability to adapt to the situations that surround it. A perfect example of natural selection at work would be the Ground Finches’ ability to survive a drought that occurred on Daphne Major in the Galapagos Island from 1976-1978. This drought alone caused the finches’ population to drop from a whooping one thousand two hundred to a mere one hundred-eighty. Despite this two year drought the ground finches did not go belly up.

The ground finches of Daphne Major lived off of the various seeds that could be found around the island. Because of their small beak size the finches tended to mostly eat off the soft easy access seeds, however as the drought progressed the soft seeds were quickly consumed and all that was left were the harder and more difficult seeds. As the finches began to drop off an adaptation came about. Within a few generations the ground finches began growing larger beak sizes that allowed them to crack open the harder shells and survive the drought. Finches with large beak sizes produced offspring with large beak sizes and so on, eventually only a small number of small beaked finches survived and the large beaked finches mainly dominated the population. It was the small beaked finches though that were more likely to survive their juvenile period due to the fact that they required less food to survive than the big beaked finches.

With these two extremes facing off against each other a middle ground had to be reached. Beak sizes shrank down to a size that was large enough to access the larger and harder seeds, yet at the same time the size was small enough that parents would be able to provide food and water to their offspring with minimal fuss. This process which produced a stabilized selection is what is referred to as equilibrium.

“How did the discovery of genetics clarify how new “variation” is introduced into a species? How did an understanding of how genes are passed along from one generation to the next populations lead to our understanding another powerful mechanism of evolution, albeit in the absence of natural selection?”

Now one of Darwin’s main errors in his book was that he could not provide a solution as to how new variation could be introduced into the population. For example by utilizing Darwin’s theories a tall person mating with a short person would create an offspring with medium height, eventually medium height would be the norm so to speak and tall and short would be eliminated from the gene pool. This is obviously not true, yet it does beg the question “how is new variation introduced to a species?”

Gregor Mendel, a Silesian monk, stepped back and took a simplified but very astute observation on this subject, his test pilots – mere pea plants. Mendel realized that by looking at complex organisms with many different solutions without even knowing how to construct the problem was futile and so he took a large population of pea plants and looked for just two things: smooth or wrinkled pods, and yellow or green peas. By doing this Mendel came to realize two wonderful things:

1. The observed characteristics of organisms are determined jointly by two particles, one inherited from the mother and one from the father.
2. Each of these two particles or genes is equally likely to b transmitted when gametes (eggs and sperm) are formed.

Mendel’s studies led to the discovery of recessive and dominate traits. While

observing his many pea plants Mendel noticed that pure green plants would produce pure green offspring when crossed with others of it’s kind, as did the yellow. He also noticed though that if you mixed one pure type green with one pure type yellow the first generation of offspring would produce pure yellow, but the second generation would produce 1 green for every yellow thus the discovery of recessive and dominate traits.

Mendel’s work although not acknowledged in his time was what truly changed our view of variation. With his discoveries it became apparent that through genes we could inherit all sorts of different traits, and should some sort of catastrophe occur there was a good chance that at least a handful of species could survive because of the different sorts of combinations each organism receives from their parental units, which in turns gives them many possibilities for adaptation.

Another way to introduce new variation into a population is via a method known as genetic drift.

Genetic drift is defined as: “a random change in gene frequencies due to sampling variation that occurs in any finite population” For an example of genetic drift at work one would only need to turn to the Amish of North America. The Amish form small communities that rarely allows outsiders to enter and even more rarely allows one of it’s own to leave the fold. One of the founding figures of these communities carried the gene for Ellis Van Crevald Syndrome which basically led to the recipient being born with six fingers instead of five. Now because most Amish can trace their family history back to the original settlers and have interbred numerous times they are all at high risk for this syndrome.

“Does natural selection and genetic drift always lead to the formation of new species? What is a species and what mechanisms lead to the appearance of new species? Are the differences between species always small?”

However genetic drift and natural selection do not always lead to the formation of a new species, rather it leaves the door open for nature to step in and rearrange the equation in order to find a solution. Sometimes mutations or adaptations are all that is needed for a species to survive the times and thus you have a variation of the original species. In order to better understand the differences one must of course know what a species is. A species is simply a group of organisms that can interbreed and produce viable offspring.

Now a fine example of adaptation rather than the creation of a new species entirely are the ground finches of Daphne Major. Rather than become entirely new birds altogether the finches beak size changed to adapt to the change in their environment, and once the event had passed because went back to its former size.

However, mutations, adaptations, natural selection, genetic drift can cause populations of organisms to evolve through time into a new species; this is what is known as microevolution. Microevolution affects the morphology, physiology, and behavior of particular species in particular environments. Macroevolution however is made up of species, genre families, and higher groupings. As you can tell the differences between species are not always large or vast, nor are they small either.

Now take for example the chordates on our planet, they evolved from the juvenile stage of a sea squirt. There was a mutation in the reproductive system of some of these tunicates which caused the juvenile to fail to develop into the adult stationary barnacle form. Somehow the mutation did not affect the reproductive organs of the juvenile, who then mated with others who carried that same mutation as well. Eventually this created the first population of organisms (species) with spinal chords.

What is cladogenesis? How does an evolutionary or phylogenetic tree that is built using the concept of cladogenesis, differ from the staircase leading to humans? What are common ancestors and how do cladists use shared derived rather than primitive traits to reconstruct the relatedness of animals and the common ancestor? What two approaches are used to reconstruct what the “common ancestors” in human evolution were like in terms of morphology and behavior? What has to be true of behavioral traits for them to be included on a cladogram? Does speaking English, manufacturing automobiles, or flying rocket ships to the moon belong on a phylogenetic tree? Give an example of human behaviors that do belong on a phylogenetic tree.

Many look at a cladogram and argue that there is absolutely no way that humans could have evolved from a monkey. In a way they are right, we didn’t evolve from a monkey, they’re a whole separate clade from us; actually we evolved from the apes. However the reasons people think that we could not have evolved from apes/monkeys is for very unscientific and egotistical purposes.

It is argued that a “monkey” could never do calculus (without us training it), could never create a language and could never even understand the concepts of fine art. These traits, albeit true, are not what make up a clade. Cladists look at the traits that count that allows us to trace our lineage back to our common grandfather species that birthed us all. An example of such a trait would be bipedal movement, a flat and wide sternum opposed to a narrow and pronounced one, or even the presence of toe bones in a foot rather than phalanges.

The previous abilities mentioned are merely learned behavior where as the later traits are derived and primitive traits that allow cladists to link together the missing pieces of the evolution chart. Now there are two methods that are used to reconstruct the common ancestors these are; cladogenesis and anagenesis.

Anagenesis takes a slowly evolving line and painstakingly reconstructs it from the first bipedal apes (Australopithecus) to modern Homo (humans). Essentially it seeks to find the “missing links” in the fossil record, which is quite a bit. Anagenesis then assumes that these links are in fact small stages that humans passed through in order to reach their current form. Darwin himself was an anagenesis believer.

Cladogenesis however doesn’t spend time looking for “missing links” or even small intermediate stages. Cladogenesis looks for the grandfather species that split off into two or more species that birthed our species, the “common ancestor”. This is the view that accepts that major morphological and physiological changes between both the parent and daughter species can occur over a short span of time. Refer back to the tunicates (sea quirts); their new species was created in just a few generations. In comparison to other events of nature and the longtime periods that it can take some organisms, the sea squirts evolved over night.

Cladists look at primitive and derived traits, but what are these? Primitive traits are traits inherited from a distant ancestor and are shared by a large number of organisms (clades). Now a derived trait is a trait that first appeared or is unique to a common ancestor of a particular clade. Phalanges are a primitive trait because they are shared with several clades, however they’re non existence on the feet of a human is derived because no other primate clade shares that trait and it first appeared in our clade.

What implications does the 21^st century view of evolution have for viewing humans as part of nature, and populations of humans relative to one another? For example, are some human populations more evolved than others? Are the technologically more advanced societies necessarily the ones whose physical traits will dominate our species in the future? Are rich people biologically superior to poor people? Are Christians biologically superior to Buddhists? Have homo sapiens stopped evolving? Are we the end product of evolution to which all other animal and plant life must be sacrificed?

Now just because we have become highly evolved does not mean we are the be-all in the evolutionary chart. We can not compare with the likes of tigris and arachnids and so on because they are a totally different species than us. Even Lemurs and Lorises can not be compared to us because although they share a common ancestor with us they are not from our clade.

A major problem that arose during the 1920’s and onward was the creation of Social Darwinism. Social Darwinism was in fact attributed to the cause of both world wars, and even had one of our own presidents vehemently opposing it. Social Darwinism is the belief that one population of humans is superior or more highly evolved to another due to race, color of skin, income, religion, and technology. Needless to say Social Darwinism is wrong was really just a pretty name for racism.

No one population of humans is superior to another for each has a variety of traits that are unique to their population that allows them to adapt and survive. If humans are to survive they must have a wide variation in order to meet the many challenges that nature can produce, a prime example of this would be the Black Death (bubonic plague). This plague raged through Europe during the middle ages and wiped out large numbers of people rich and poor, however humans began to develop immunity to the plague and thus survived. This survival can be attributed to the variation that could be found in the human population at that time. Without variation humans would have ceased to exist a long time ago.

This is not to say that we have stopped evolving, although we can not see the changes with our own eyes everyday humans evolve a step further. New genes are produced that carry the immunity for diseases that ravage our population. An example of this is none other than myself.

I was bitten by a mosquito back in early August that carried the West Nile Virus. Other than a slight rash and raising of the bite on my arm, a small brown spot that began to look like a sort of birth mark, and a few dizzy spells and headaches I suffered none of the more violent symptoms and did not require any medical treatment. Although I was not completely immune to its effects my system was able to fight off the stronger aspects of the virus without medical aid. This is an example of how we still continue to evolve even to this day.

When we finally do stop evolving it will because no room for variation exists within us any longer and that will be a sad day indeed, because extinction is right around the corner.