Evolutionary Theory and Evidence: Patterns, Processes, and Scientific Reasoning in Biology

Introduction to Biology and Scientific Reasoning

Definition and Scope of Biology

Biology is the scientific study of life, focusing on understanding the diversity and unity of living organisms. Biologists seek observations and ideas that unify our understanding of life’s complexity.

• Observation: Gathering information about the natural world.

• Pattern: Recognizable regularities or trends in nature.

• Process: Mechanisms that produce observed patterns.

Scientific Method in Biology

The scientific method involves systematic observation, hypothesis formation, and testing to explain natural phenomena.

• Hypothesis: Proposed explanation for a specific observation, often involving a process.

• Prediction: Statement about what would be expected if the hypothesis is correct.

• Theory: Broad explanation supported by a large body of evidence; often composed of patterns and processes.

Theory of Evolution by Natural Selection

Components of Evolutionary Theory

Evolution via natural selection (ENS) explains how organisms adapt to their environment, resulting in increased fitness.

• Adaptation: Trait that increases an organism’s fitness (ability to survive and reproduce).

• Fitness: The reproductive success of an organism in its environment.

• Natural Selection: The process by which heritable traits that confer a reproductive advantage become more common in a population over time.

Examples of Evolutionary Hypotheses

• Food Competition Hypothesis: Giraffes compete for access to food; long necks allow access to higher foliage.

• Mate Competition Hypothesis: Long necks increase access to females through fighting; males with longer necks win more fights.

• Prediction: During dry seasons, giraffes feed higher in trees; males with long necks win more fights than short-necked males.

Historical Theories of Species Origin

Theory of Special Creation

This theory posits that each species was created independently by a divine creator for a specific location and habitat.

• Pattern: Species are independent and unchanging.

• Process: Creation by divine or supernatural agency.

• Typological Thinking: Species are unchanging; variation is unimportant.

Evolutionary Theories

• Lamarckian Evolution: Species change over time; inheritance of acquired characteristics.

• Process: Individuals’ phenotypes (observable traits) change and are inherited by offspring.

Darwin’s Theory of Evolution

Key Patterns and Processes

Darwin’s revolutionary idea challenged the theory of special creation, proposing that species change through time and are related by common descent.

• Pattern:

  • Species change through time.

  • Species near one another in time or space are more similar.

  • Species are related by ancestry due to common descent.

• Process: Natural selection occurs when heritable variation in traits leads to improved reproductive success for some individuals (differential reproductive success).

• Key Insights:

  • Population thinking: Individuals in a population vary.

  • Evolution occurs because individuals with certain traits leave more offspring than others.

  • Descent with modification produces new, modified species from ancestral species.

• Predictions:

  • Species change over time.

  • Species are related by common ancestry.

Evidence for Evolution

Fossil Record

Fossils are traces of organisms that lived in the past. The fossil record is the totality of all fossils found and described.

• Relative Dating: Determining the age of fossils based on their position in sedimentary layers (lower strata = older fossils).

• Radiometric Dating: Uses isotopes to determine the absolute age of fossils by measuring the conversion of unstable parent atoms into daughter atoms.

Key Equations:

• $\text{Absolute Age} = \text{Time since formation based on isotope decay}$

Based on radiometric dating:

• Earth is approximately $4.6$ billion years old.

• Life began between $3.4$ and $3.8$ billion years ago.

Transitional Features

Transitional fossils show intermediate forms between ancestral and derived species, providing strong evidence of change over time.

• Example: Fossil record of gradual change from aquatic form to four-limbed terrestrial form.

• Law of succession: Fossil species are often similar to living species in the same geographic area.

Vestigial Traits

Vestigial traits are reduced or incompletely developed structures that have no or limited function but are related to functioning structures in other species.

• Examples: Goosebumps in humans, reduced wings in flightless birds.

Species Related by Common Ancestry

Biogeography

Biogeography is the study of the geographic distribution of species.

• Example: Galápagos Islands—distinct species on different islands, but striking similarities among species, supporting Darwin’s hypothesis of common ancestry.

Homologies

Homologies are similarities in species that exist due to descent from a common ancestor.

• Genetic Homology: Similarity in DNA nucleotide or amino acid sequences.

• Developmental Homology: Similar embryonic traits, such as pharyngeal pouches.

• Structural Homology: Similar anatomical structures.

Key Point: Homologies provide evidence for common ancestry and evolutionary relationships among species.

Additional info:

• Examples of rapid evolution include bacteria/insects evolving drug/insecticide resistance, bird migration changes, and floral blooming shifts due to climate change.

• Theodore Dobzhansky is referenced as a key evolutionary biologist ("Nothing in biology makes sense except in the light of evolution").