Modification of body parts

MODIFICATION OF BODY PARTS

CHARLES DARWIN AND HIS THEORY OF EVOLUTION

• Birth and Early Life

  • Charles Darwin was born in 1809.

  • At 22, he embarked on a voyage on the HMS Beagle as a naturalist, from 1831 to 1836, studying various plants, animals, and geological formations.

• Observations Leading to Theory

  • Noted variety in species, both living and extinct and slight differences between species, leading to the understanding of adaptations.

  • Developed his theory of evolution through natural selection and descent with modification in 1859 after extensive evidence study.

  • The concept where new species emerge from pre-existing species over time.

CONNECTIONS BETWEEN LIVING AND EXTINCT SPECIES

• Homologous Structures

  • Different animals with common basic structures, indicating a shared evolutionary lineage (homologous structures).

  • These structures may have been modified to serve different functions.

• Descent with Modification

  • Links living species with extinct species through shared characteristics, proving genetic connections.

ADAPTIVE RADIATION

• Adaptation to Environments

  • Members of a species adapt to different environments from an ancestral stock, helping them survive and reproduce.

  • Over time, this process results in the modification of body plans and spawning of new species.

DIVERGENT EVOLUTION

• Morphological Divergence

  • Development of distinct structural features in organisms from the same ancestral source termed divergent evolution, allowing species to exploit various ecological niches.

HOMOLOGIES

• Characteristics of Homologies

  • Similar fundamental structure, position, and development in organisms; may differ superficially and not all perform the same function.

  • Indicator of evolutionary relationships among species that diverged from common ancestors.

• Examples of Homologies

  • Forelimbs of mammals, such as birds, bats, and whales, modified for various movements and functions according to the organism's needs.

  • Adaptations noted in insect mouthparts and flower structures for pollination compatibility.

PENTADACTYL LIMB

• Definition and Origin

  • The pentadactyl limb, characterized by five digits (fingers/toes), exists in all vertebrate classes.

  • Can be traced back to amphibious fin fossils linked to early terrestrial life.

MAMMALIAN FORELIMB ADAPTATIONS

• General Characteristics

  • The pentadactyl forelimb showcases bone structural similarities despite different shapes across species.

  • Example: Similarities between the bone structures of whale flippers and human arms suggest a common ancestry, modified through natural selection.

• Primates' Adaptations

  • Primates showcase traits for manual dexterity (e.g., opposable thumbs for grasping).

  • An elongated phalange structure in tree-dwelling monkeys aids in swinging in their habitats.

COMPARING HUMANS AND AFRICAN APES

• Common Ancestry

  • Research indicates humans and African apes did not evolve directly from one another; rather, they share a common ancestor that diverged about 6 million years ago.

• Anatomical Similarities

  • Upright posture, absence of external tails, free arm rotation, opposable thumbs, stereoscopic vision, and sexual dimorphism are notable features among living hominins.

• Anatomical Differences

  • Structural differences linked to bipedalism in humans, while African apes exhibit tree-climbing abilities and knuckle-walking.

  • Key adaptations for humans include a shorter and broader pelvis, longer femurs, and a specialized foot structure supporting efficient upright locomotion.

EVOLUTIONARY ADAPTATIONS IN STRUCTURES

• Humans vs. African Apes

  • Differences include arm length, digit structure, and skeletal adaptations suited for habitual bipedalism in humans and quadrupedal knuckle-walking in apes.

• Brain and Cranium Variations

  • Humans possess a larger brain with advanced cognitive functions compared to African apes. Differences in skull morphology relate to dietary and locomotor adaptations.

ADAPTATIONS OF MAMMALIAN FORELIMB - EXAMPLES

• Ungulates

  • Hooved animals optimized for strength and endurance in quadrapedal locomotion.

• Moles

  • Have short forelimbs evolved into effective digging tools with specialized structures aiding in soil excavation.

• Whales

  • Flippers adapted from forelimbs for aquatic maneuverability, showcasing modified proportions for swimming.

• Bats

  • Adaptations for flight include elongated finger bones that form wing structures for gliding.

EVIDENCE FOR EVOLUTION: VESTIGIAL ORGANS

• Definition

  • Vestigial organs appear diminished or non-functional compared to their homologous structures in other species.

  • Their existence provides compelling evidence for shared ancestry among species exhibiting evolutionary changes over time.

• Examples

  • Human tailbone (coccyx), an appendix, and pelvic structures in dolphins serve as reminders of past functional forms.