Science With Mr. Milstid

So far, throughout this unit we’ve been discussing similarities and differences between organisms as it relates to classification.
But how did we get all those different organisms? How can there be so many different types of creatures on the planet?
The standard scientific explanation is: evolution by means of natural selection.
What is evolution?
Evolution is, simply, the process of gradual change over time.
This process is supported by several key pieces of evidence: Fossils & the Fossil Record, Common Characteristics, and DNA & Genetics.

Fossils: evidence of evolution
Sometimes, the remains or imprints of once-living organisms are found in layers of rock that make up the earth. These remains are called fossils.
Fossils can be created when an organism dies and its body is preserved, when an organism steps in mud and leaves a footprint that is preserved, etc., etc.
By looking at where fossils fall in the geologic column, scientists can classify them and get an idea of the basic age of a fossil. Through this process, scientists have been able to make a general timeline of the history of life on earth. This timeline allows scientists to look at different organisms that existed on earth, the order they existed in, and compare how they changed over time – providing evidence for evolution.

 


 
Comparative Anatomy: evidence of evolution
Another way scientists determine evolutionary ties is by examining similar traits and characteristics of different animals.
By looking at similar bone structure, for instance, scientists can see relationships that exist between animals that may not seem to be related.
For instance, The structure and order of bones of a human arm are similar to those of the front limbs of a cat, a dolphin, and a bat. These similarities suggest that cats, dolphins, bats, and humans had a common ancestor.



One excellent case study in this process is the analysis of the fossil remains of Pakicetus, a genus of extinct cetaceans found in the early Eocene in Pakistan (as presented in the video at the top of the post). Fossil remains of this creature suggest that it is a transitional species between extinct land mammals and modern ocean mammals such as whales.
The simulation below provides a wonderful investigation of this concept. Explore the simulation to help solve the mystery of whale evolution.

 


 
Common DNA: evidence of evolution
Yet another way scientists prove evolutionary ties is by examining an organism’s DNA (or genetic code).
Species that have many traits in common have similarities in their DNA; the more closely related two organisms’ DNA is, the more closely linked they are, evolutionarily.

 

 
Charles Darwin: Father of the Mechanics of Evolution
Though several other scientists at the time developed similar, parallel theories regarding evolution, Charles Darwin is regarded as the father of the mechanics of evolution. That is, he was the first to develop an explanation for how evolution really works.

When Darwin was a young man he traveled around the world on the H.M.S. Beagle (1831-1836), a research vessel. His job was to make observations on the plants and animals found in the places the ship docked.
While on the trip, Darwin saw many strange and new plants and animals and began to wonder how they could have come to be. He was particularly struck by the animals of the Galapagos Islands, where he found that each island had a different kind of tortoise, a different kind of finch, and a different kind of marine iguana.

There are thirteen species of Darwin’s finch, a small sparrow-like bird, in the Galapagos Islands. Each species has adapted – or evolved – depending on the type of food that it feeds on. This is shown by the different beak shapes.
For example, the large ground finch has developed a broad, wide beak, for cracking hard seeds. The cactus ground finch has a long, down curved beak, for reaching down into the cactus flowers upon which it feeds. Other types of finch feed on insects, some remove ticks from tortoises, and one even pecks at seabirds and feeds on their blood! Each finch species has evolved according to its particular food source.

 


 


* The simulation above matches finches with the food source to which they are adapted. Pay close attention to the shape and size of their beaks, and the food they eat. This is essentially what Darwin did in the Galapagos Islands.

 
Having witnessed the variation among species on the islands, Darwin formed his theory of evolution, in which he proposed that species evolve by means of natural selection.

Natural selection is fairly simple in process.
Essentially, organisms begin to develop adaptations to their environment. These are characteristics that help an organism survive and reproduce. They are caused by genetic variation, etc.
Over time, organisms that are more suited to their environment begin to become the dominant version of their species.
For example – organisms that have a color variation that blends in with their environment will tend to be eaten less by predators, as they are more difficult to see. Over time, more and more of these organisms will be left to breed, while the versions of their species with less advantageous color will become less common and breed less often. This increases the population of camouflaged organisms, and eventually, the entire species will be populated by this variation.

This is Outlines in Darwin’s 4 Part Theory of Natural Selection
1. Overproduction: Organisms produce more offspring than will survive.
2. Inherited Variation:Each individual offspring has different traits than the parents that it came from
3. Struggle to Survive: Some offspring may be killed by predators or be incapable of collecting enough food (etc.), and only the fittest will survive to breed.
4. Successful Reproduction: Only the organisms best adapted to their environment will reproduce and pass on their genes to a next generation of offspring.

A wonderful example of adaptation and variation is seen in the simulation below. It showcases a real-world example: the pepper-moth.

 


 

Causes of Adaptations:
• Resistance - Happens when organisms develop a resistance to an external poison or bacteria. Over time, the entire population is no longer affected.
  Example: Insecticides have been used so much that now more than 500 kinds of insects have developed resistance to certain insecticides.
• Competition –
  For Mates: many species have so much competition for mates that interesting adaptations result. Example, the females of many bird species prefer to mate with males that have colorful feathers, so more colorful birds will begin to be more common.
  For Food: organisms with adaptations that make it easier to eat/survive will pass on their adaptations to future generations.

The Complete Works of Darwin Online

 



The end result of natural selection/evolution is the development of a new species. This is called speciation.

The process of speciation is outlined below:
• Separation - Speciation often begins when a part of a population becomes separated from the rest.
• Adaptation - Populations constantly undergo natural selection. After two groups have separated, natural selection may act on each group in different ways.
• Division - Over many generations, two separated groups of a population may become very different until the point when they can no longer mate with one another. At this point, the two groups are no longer the same species.

Tags: Adaptation, Darwin, Evolution, Natural Selection, Speciation, Species
Posted in Biological Science