Evolution: Fossils and Homologous Structures

• Individuals within a species exhibit variation; those with advantageous traits are more likely to survive and reproduce.

Fossil Record

• Indicates types of plants and animals that existed in the past.
• Scientists compare fossilized body structures and movement traces to understand how organisms changed.
• Scientists analyze structural similarities in fossils from different species to determine evolutionary relationships.
• The discovery of transitional fossils enhances understanding of the evolutionary process.
• Gaps in the fossil record occur due to missing transitional fossils.
• Transitional fossils showcase the transformation from ancestral forms to descendant species' forms.
• The fossil record tracks human evolution from apes and identifies divergence points between humans and chimpanzees.

Homologous Structures

• Structures inherited from a common ancestor, but have different functions.
• Examples include the humerus, radius, ulna, carpals, metacarpals, and phalanges.
• Provides evidence for organism evolution from a common ancestor.

Analogous Structures

• Body parts with similar functions, but not the same structure.
• Organisms with analogous structures do not share a common ancestry.

Vestigial Structures

• Structures that were once useful, but no longer serve a purpose in the organism.
• Can negatively impact an organism by requiring energy and space, potentially posing health risks.

Embryological Development

• Embryo: An organism in its earliest stages of development, before hatching or birth.
• Vertebrate embryos (fish, amphibians, reptiles, birds, and mammals) initially share features like gill slits, tails, and segmented muscles, indicating shared ancestry.
• The phylotypic stage demonstrates similarities among vertebrate embryos, supporting shared ancestry, but embryos develop into distinct adult forms.
• Specialized traits develop later in evolution.
• Haeckel's law suggests that embryonic development mirrors species' evolutionary history.

DNA

• Scientists compare DNA codes to determine animal relatedness.
• Closely related species have highly similar DNA.
• Humans and chimpanzees share approximately 98% of their DNA.
• Hox genes regulate body plans in embryos across species, indicating a shared evolutionary blueprint.
• All multicellular animals pass through the blastula stage, suggesting a common origin.
• Molecular clocks use DNA mutation rates to estimate species divergence times.
• Mutations, which are random DNA changes accumulating over generations, help measure evolutionary time.
• Observed lineages: Humans, Mammals, Reptile-like, Amphibian-like, fish-like, segmented worms

Antibiotic Resistance

• Illustrates evolution through natural selection, as bacteria evolve to survive antibiotics due to rapid reproduction and genetic variation.

Cladogram

• Visually represents evolutionary relationships among species using a branching diagram.
• Branching points (nodes) represent common ancestors.
• Branches signify species or groups of species evolving from ancestors.
• Clade: A group of species sharing a common ancestor & all descendants.
• A clade is represented by each branch and includes the sub-branches.
• Shared traits evolve over time towards the branch tips called derived traits.
• Reading from left to right or bottom to top indicates evolutionary progression, with older species towards the bottom or left and newer species at the top or right.

Homologous Structures Summary

• Homologous structures are body parts that appear in different species but have a similar underlying structure.
• Forelimbs of humans, bats, and whales are examples

Analogous Structures Summary

• Analogous structures perform similar functions in different species but do not share a common evolutionary origin.
• Wings of birds and insects arise from convergent evolution.
• Convergent evolution occurs when species in similar environments face similar selective pressures.

Vestigial Structures Summary

• Vestigial structures are body parts or organs that have lost their original function through evolution.
• Examples include the human appendix or the pelvic bones in whales.

Embryological Development Summary

• Vertebrates show similar early features like gill slits, tails, and segmented muscles.
• Similarity in early development reveals shared ancestry, adapting to environments.
• Embryos transform into distinct adult forms, evolution shapes species at every stage.

Fossil Record Summary

• The fossil record shows history of the gradual changes in species over millions of years.
• Fossils of extinct species provide evidence of organisms and how they evolved.
• Scientists can trace evolution of traits and organisms to understand how life adapts.