Origin and Evolution of Life: From Cells to Humans
Modern Theories on the Origin of Life
Chemical Evolution
The primitive atmosphere’s chemical compounds facilitated the synthesis of simple organic compounds essential for life. This early atmosphere lacked free oxygen. Gases reacted through intense radiation, forming small organic molecules. Rain washed these chemicals into the oceans, creating the “primeval soup.” These molecules reacted with water, forming biological building blocks. These interacted, forming giant molecules. Microstructures emerged in the primeval soup, grouping polymers and initiating biological evolution.
Mineral Genesis
Biological polymers likely synthesized on clay surfaces in the primeval soup, as water molecules hindered solidification.
Hydrothermal Vents
Life may have begun in deep ocean hydrothermal vents. These vents offered dissolved gases from volcanic eruptions and high temperatures (over 200°C). Pyrite provided scaffolding for organic polymer formation.
The RNA World
RNA, capable of storage and catalysis, is believed to be the first biomolecule. It formed in oceans rich in amino acids and proteins. DNA later replaced RNA due to its greater stability.
Cellular Evolution: The First Cell
(See diagram)
All organisms are related, descending from ancestral cells. The appearance of a biological membrane was crucial. This membrane separated the internal environment, enabling primitive metabolism, energy acquisition, reproduction, and response to environmental changes. The first cells were likely anaerobic fermentative heterotrophs, obtaining energy directly from their environment. They evolved into cyanobacteria, developing photosynthesis to convert solar energy into carbohydrates, releasing oxygen. This transformed the atmosphere, making it oxidizing. Many anaerobic organisms perished, while others adapted to use oxygen in metabolic reactions. Aerobic heterotrophic bacteria evolved, using atmospheric oxygen for energy through cellular respiration, releasing carbon dioxide.
Evolution of Living Beings
Fixism proposes that species remain unchanged since creation. Catastrophism suggests geological cataclysms destroy species, leading to new creations. Lamarck’s hypothesis of transformations posits gradual evolution between species. Darwin’s theory of evolution connects all living beings through adaptive divergence from preceding species.
Darwin’s theory is based on:
- High Reproductive Capacity: More offspring are born than survive, but populations remain stable due to limited resources. Individuals compete for food and reproduction.
- Stock Variability: Individuals have heritable characteristics. Some have better survival and mating chances due to competition.
- Natural Selection: Only the fittest survive, reproduce, and transmit advantageous traits to offspring.
- Species Evolution: Surviving individuals transmit changes, leading to new species over generations.
Scientific Evidence of Evolution
Classical Evidence
- Morphological: Comparative anatomy reveals similarities and differences in organs across species.
- Homologous structures result from divergent evolution from a common ancestor (e.g., vertebrate limbs).
- Analogous structures develop similar functions through adaptation (e.g., butterfly and bird wings).
- Paleontological: Fossils (mineralized remains) reveal past life forms and their evolutionary relationships with current species.
- Embryological: Embryonic development similarities in vertebrates suggest common ancestry. Haeckel’s recapitulation principle states embryonic development mirrors evolutionary development.
- Taxonomic: Classification groups organisms with similar characteristics, reflecting common evolutionary processes.
Recent Evidence
- Comparative Biochemistry and Cell Biology: Chemical unity (e.g., genetic code, ATP, metabolic processes) indicates common ancestry.
- Protein and RNA Sequences: Similarities in gene or protein sequences reflect evolutionary closeness.
- DNA Hybridization: DNA’s ability to renature and reassemble reveals evolutionary relationships.
- Banded Chromosome Study: Longitudinal differentiation of chromosomes provides insights.
- Immune Analysis: Antibody responses vary based on evolutionary distance.
Biodiversity: The Result of Evolution
A species is a group of morphologically similar organisms that can reproduce, producing fertile offspring, and are reproductively isolated. Speciation occurs when populations become reproductively isolated, often due to geographic isolation, leading to new species.
Classification of Living Things
Taxonomy classifies living things. The binomial system names species with two Latin words (e.g., Homo sapiens, where Homo is the genus).
Origin of the Human Species
The Primate Order
Primates are mammals originating about 75 million years ago. Key features include:
- Highly mobile forelimbs with opposable thumbs.
- Stereoscopic vision due to forward-facing eyes.
- Unspecialized digestive systems for varied diets.
- Limited offspring with high maternal dependency.
The Process of Humanization
Hominid evolution is linked to climate change, forcing primates from arboreal life. Bipedalism offered advantages: better vision over savannah grasses and freed hands. Lower limbs lengthened, pelvis widened, and the big toe lost opposability. Hands gained mobility and precision. Diet diversified, including meat, reducing tooth wear. Encephalization (brain size relative to body size) increased due to a richer diet, social activities, brain growth during gestation, and extended childhood.
- Orrorin tugenesis: Oldest bipedal hominid (6 million years ago).
- Australopithecus: Bipedal, arboreal (4-2 million years ago).
- Paranthropus: Africa (2-1 million years ago).
- Homo habilis: Africa (2.5 million years ago), first toolmakers.
- Homo ergaster: Africa, Europe, Asia (1.9 million years ago).
- Homo erectus: Europe, Asia (1.6 million – 100,000 years ago), used fire.
- Homo antecessor: Atapuerca (1 million years ago).
- Homo neanderthalensis: Europe (200,000 years ago), hunters/gatherers.
- Homo sapiens: Africa (200,000 years ago), present.
Kittens and Monet. Oh the Monet!