Evidence and Theories of Evolution: Fossils, Embryos, Molecules

Evidence of Evolution

Paleontological Evidence

Intermediate fossils: Archaeopteryx and Tiktaalik.

Other fossil series: a series of fossil mollusks and the evolution of the horse demonstrate transitional forms and gradual change over time.

Morphological Evidence

Data: all vertebrates share a common pattern of limb types (e.g., chiridium) — Mennecke's observations highlight homologous structures across taxa.

Conclusion: morphological similarities support a common ancestor for vertebrates.

Vestigial Organs

Vestigial organs: structures that are functionally reduced or useless in the modern organism but were useful in ancestral species.

Conclusion: species that retain vestigial organs often inherited them from ancestors in which those organs had a function.

Embryological Evidence

Data: the embryos of different vertebrate types are often difficult to distinguish at early stages; they show common developmental patterns.

Conclusion: embryological similarity provides evidence for a common ancestor.

Molecular Evidence

Data: all living beings share the same basic molecules (DNA, RNA, proteins) and use the same genetic code.

Conclusion: molecular similarities indicate that all living organisms share a common ancestry.

Historical Theories of Evolution

Before the 18th Century

- Mythological explanations were common for the origin of the world.

- Judeo-Christian culture (Genesis): fixism and creationism held that species are immutable and the world was created by God (intelligent design).

In the Eighteenth Century

- The traditional ideas began to be questioned.

- Transformism (the idea that species change over time) emerged as an alternative view.

Lamarck's Theory

1809: Zoological Philosophy and Contributions

In 1809 Jean-Baptiste Lamarck published Philosophie Zoologique. It was the first coherent, detailed book on evolution. Lamarck rejected the concept of fixed species and emphasized the influence of the environment as a major factor in evolution.

Theory

1. The environment changes.
2. Organisms strive to adapt. When organisms are forced by environmental circumstances to use an organ continually, that organ becomes developed and strengthened; conversely, when an organ is no longer useful it weakens and deteriorates.
3. Inheritance of acquired characters: the development or deterioration of a particular organ (i.e., a character acquired during an individual's life) is preserved and transmitted to subsequent generations.

Criticisms

Lamarck's theory was considered too specific, based on few observations and lacking experimental support. The inheritance of acquired characteristics is now known to be generally unsupported as a primary mechanism of evolution.

Darwin and His Theory of Evolution

Voyage of the Beagle

Charles Darwin traveled for five years on the voyage of the Beagle, collecting observations and specimens that informed his later work.

Publication

In 1859 Darwin published On the Origin of Species.

Darwin's Contribution

1. He provided a meticulous compilation of observations and evidence for evolution.
2. He proposed a mechanism called natural selection as the primary process driving the evolution of species.

Artificial Selection

The artificial selection practiced by breeders and farmers was crucial to Darwin's understanding and development of the concept of natural selection.

Bases of Darwin's Theory

1. More individuals are born than can survive.
2. Individuals in a population are not identical: they show variations, and many of these variations are heritable. Some variations confer an advantage for survival.
3. Variations that confer advantages improve an individual's success in competition with others in the population.
4. The best-adapted individuals are more likely to survive and leave a larger number of offspring, causing advantageous traits to become more common in subsequent generations.