⬅ Previous Lesson Workshop Index Next Lesson ➡

Fossils, Evolution, & Diversity

Objective

In this lesson, you will review genetic diversity. Scientists, regardless of their specialization, need to possess a basic level of science literacy across all disciplines. This lesson provides an overview of the major concepts pertaining to fossils, evolution, and diversity that all students of the sciences should know. The chapters that follow will focus in greater detail on these ideas.

Previously Covered:

Genetic information is passed from generation to generation via DNA.
Genetic diversity is increased through sexual reproduction and changes in the genetic code, or mutations.
Genetic diversity is advantageous for species under changing environmental conditions.

Now we will see that genetic change is the mechanism of evolution.Fossils are the remains of once living things that were preserved in the Earth’s crust. Fossilization most often occurs when the remains of an organism become covered by sediments or volcanic ash. Metal ions and inorganic compounds in solution harden in the bones and tissues. As sediments build up, pressure is exerted on the hardening remains, solidifying them. Often the hard parts of a living organism leave an impression in the sedimentary rock that provides an imprint of their body structure. These imprints have provided valuable clues into the body styles of pre-existing plants and animals.The method by which fossils are formed also gives a clue to their relative ages. This was something determined by Charles Lyell, a geologist, and Georges Cuvier, an anatomist who studied fossils. By the early 1800s, geologists and naturalists had recognized that species change over time. Darwin did not come up with the idea of evolution. His major idea was simply an explanation for how evolution might have happened: the process of natural selection. In fact, Darwin and a fellow named Alfred Wallace developed the idea of evolution through natural selection at the same time. They presented their ideas together; however, it was Darwin’s book The Origin of Species that got all the attention.

Charles Lyell

Georges Cuvier

Alfred Wallace

Charles Darwin

The distribution of vertebrate fossils and species played a big part in Darwin’s work. The position of fossils in the geologic strata showed a progressive change from ancient to modern organisms. Fossils found in Australia resembled modern species in Australia; fossils in Africa more closely resembled modern African species. Darwin found this to be true for each of the continents he visited during the voyage of TheBeagle.

Fossil evidence for plate tectonics

Both Darwin and Wallace proposed that variation within a species of organisms was due to nature acting on certain characteristics to favor reproductive success for some individuals over others. Like Mendel, Darwin and Wallace knew about artificial selection, the intentional manipulation of inherited traits of plants and animals by people. They proposed that nature might act in the same way, and that over very long periods of time, species would be expected to change as a result.

Fossil trilobyte

To Darwin, survival of the fittest did not mean that the biggest and strongest organisms would live the longest. To Darwin, fitness was about reproductive success. What survived were not individuals, but characteristics that were passed from generation to generation. Characteristics that lead to greatest adaptation increase fitness. Darwin and Wallace figured out, unlike Jean Baptiste Lamarck before them, that it was species that change, not individuals.

Question

Besides Darwin, who also developed the idea of evolution through natural selection?

Jean Baptiste Lamarck
Charles Lyell
Alfred Wallace
George Cuvier

Reveal Answer

The correct answer is C. Wallace worked on the evolution theory at the same time as Darwin. Lamarck is considered the forerunner of evolution. Lyell was a geologist and Cuvier was an anatomist, who both studied and aged fossils.

Question

What was Darwin’s greatest contribution to evolutionary theory?

His comparative anatomy based on fossils
His description of extinction and speciation
His ideas about natural selection
His system for classifying organisms based on morphology

Reveal Answer

If you selected C, you are correct! Think natural selection when you think about Darwin. Ideas about evolution were around long before Darwin.

Pangaea

The phenomenon of continental drift also supports evolutionary theory. Earlier scientists had hypothesized about this idea, but it was Alfred Wegener (1915) who outlined the theory that Earth once had one land mass, named Pangaea. This land mass split and began to drift apart around 200 million years ago. The shape of the continents and current movement of tectonic plates supports the idea of continental drift. Species that evolved more than 200 million years ago, such as conifers and reptiles, have relatively similar fossils around the world; those that evolved later, such as mammals and flowering plants, are much more diverse across the globe.

Alfred Wegener

Today we know that the incredible diversity of life on Earth is the result of subtle changes in DNA over billions of years. The favored method for creating phylogenies is via studying conserved genes, those that code for basic life functions common to all organisms.

The way biologists keep track of all that diversity has changed over time. Long before Darwin’s time, humans classified living things based on their common characteristics. Aristotle classified organisms as plant or animal, and further subdivided those groups based on appearance or whether they were found on land, in water, or in the air!

By Darwin’s day, classification was most often based on morphology or comparative anatomy. As we learned more about heritability, reproductive modes and development became important taxonomic tools. Biochemical characteristics and modes of metabolism have often been used to classify bacteria. Today, phylogenies based on molecular genetics show us just how similar we are to all living things, despite the great diversity in life. Cladograms are a way of showing the degree of relatedness of organisms. All living things can be placed somewhere on a branch of the tree of life, as is demonstrated by the impressive Tree of Life Web Project.

Primate and insect cladograms

Today, living things are grouped into 3 domains: Archaea, Bacteria, and Eukarya. The two prokaryote domains, Archaea and Bacteria, are thought to have evolved from a common prokaryote ancestor, the first kind of living organism.

There are 6 kingdoms of organisms, the two prokaryotic domains and the eukaryotic protists, fungi, plants and animals. Modern eukaryotic cells are thought to have evolved from symbioses between early eukaryotes and bacteria, which became incorporated as mitochondria and chloroplasts.

Organisms are further classified into phylum, class, order, family, genus, and species – each of which has sub-groupings. For example, the classification for humans looks something like this:

Question

In which domain can a prokaryote be classified?

Chordata
Archaea
Animalia
Eukarya

Reveal Answer

If you chose B, you are correct! Choice A is a phylum, choice C is a kingdom, and choice D is domain, yet it is for eukaryotes.

By bringing together the concepts of heredity put forth by Mendel, ideas about natural selection developed by Darwin and Wallace, and our ever expanding knowledge of the genomes of living things, the modern tenets of biology point to an underling unity beneath the diversity of life on Earth today.

Summary

Fossils, anatomies of living things, embryonic development, and continental drift are among the evidence that supports the theory of evolution.
Although Darwin is commonly credited for the theory of evolution, there were several people who were instrumental in the development of the theory.
All living things fall into three domains and six kingdoms.

⬅ Previous Lesson Workshop Index Next Lesson ➡