Evolution, Biodiversity, and Human Origins: Core Principles

Core Concepts in Biology

Biodiversity

Species that inhabit or have ever inhabited the Earth.

Adaptation

The accumulation of changes in a living being to suit the environment in which it lives.

Types of Adaptation

• Structural: Affects organs and allows for specific functions, e.g., birds' beaks.
• Physiological: Affects the organism's function and metabolism.
• Behavioral: Actions that provide advantages, e.g., migration.

Evolutionary Theories

Biodiversity and Evolution

Slow changes in living beings over millions of years.

Fixism (Georges Cuvier)

Organisms were created through divine creation and became extinct due to catastrophes. This theory posited that species could not change, a view contrasted by later evolutionary theories.

Lamarckism (Jean-Baptiste de Lamarck)

Species transform over time through the inheritance of acquired characteristics. Key ideas include:

• Nature tends towards perfection.
• Environmental pressure leads to the development or elimination of organs.
• Changes in an organism appear in its immediate offspring.

Natural Selection (Charles Darwin)

Key principles include:

• Variability between individuals, where some traits are more advantageous for survival.
• The struggle for existence between organisms in a population.
• Survival of the fittest.
• The origin of species as a result of organisms' adaptation to their environment.

Modern Synthetic Theory of Evolution

Key tenets:

• The evolutionary unit is the population, not the individual.
• Natural selection acts on genetic variability.
• Changes in populations lead to the creation of new species.

Speciation and Evolutionary Evidence

Speciation

The process through which new species are generated from a population of a particular species, often involving geographical isolation.

Evidence of Evolution

• Paleontological Evidence: Fossils of organisms that preceded current life forms show increasing complexity and structures from previous organisms.
• Biogeographical Evidence: The geographical distribution of species.
• Comparative Anatomy: The internal anatomy of different species reveals similarities and differences that indicate evolutionary relationships.
• Embryological Evidence: Embryos of different species show similarities during early development.
• Biochemical Evidence: Cellular structures and metabolic pathways are similar across diverse organisms, indicating common ancestry.

Hominid Characteristics

• Bipedalism: Characterized by an S-shaped spine, a wide and short pelvis, a more robust femur, and improved balance, allowing for upright walking.
• Free Hands: Development of opposable thumbs, leading to the freedom of hands for tool use, manipulation, and carrying objects.
• Brain Development: Significant increase in cranium size and complexity of the brain, leading to enhanced intelligence, abstract thought, and problem-solving abilities.
• Language: The development of complex vocalizations and symbolic communication, facilitating social interaction, cooperation, and the transmission of knowledge across generations.
• Neoteny: Human beings are born in a relatively immature state, requiring a prolonged period of development, which allows for greater brain growth and learning postnatally.

Key Hominid Species

• Australopithecus: Approximately 1.10m tall, 40 kg. Walked upright. Lived 3.5 to 2.5 million years ago.
• Homo habilis: Approximately 1.59m tall, 50 kg. Known as 'handy man' for using early stone tools; may have had rudimentary speech. Lived 2.3 to 1.8 million years ago.
• Homo erectus: Approximately 1.60m tall, 60 kg. 'Upright man' who discovered fire, hunted in groups, and migrated out of Africa. Lived 1.9 million to 400,000 years ago.
• Homo neanderthalensis: Approximately 1.65m tall, 80 kg. Adapted to cold climates, practiced burials, and used specialized tools. Lived 150,000 to 35,000 years ago.
• Homo sapiens sapiens: Approximately 1.70m tall, 70 kg. Modern humans, characterized by complex art, sophisticated tools (including bone), and global distribution. Appeared around 120,000 years ago to present.

Origin of Life: Miller-Urey Experiment (1953)

This experiment aimed to reproduce the conditions of Earth's early atmosphere, which was thought to be reducing (lacking free oxygen) and containing water vapor (H₂O), hydrogen (H₂), methane (CH₄), and ammonia (NH₃).

Experimental Steps:

1. These gases were introduced into a sealed, sterile chamber.
2. Electric currents were passed through the chamber using electrodes to simulate energy from lightning storms.
3. The resulting chemical products were cooled, condensed, and collected in a container that mimicked the primitive ocean.
4. After a week, samples from this 'primitive ocean' were extracted and analyzed, revealing the formation of organic compounds, including amino acids (the building blocks of proteins), from simple inorganic precursors.

Origin of Eukaryotic Cells: Endosymbiotic Theory

The endosymbiotic theory proposes how eukaryotic cells (cells with a nucleus and other membrane-bound organelles) evolved from simpler prokaryotic organisms. It suggests that some organelles, such as mitochondria (sites of cellular respiration) and chloroplasts (sites of photosynthesis), were once free-living prokaryotic bacteria that were engulfed by larger host cells, eventually forming a symbiotic relationship.