Understanding Species Evolution
What is a Species?
A species is defined as a group of organisms capable of interbreeding and producing fertile offspring.
How Does Evolution Occur?
Natural Selection
Charles Darwin proposed natural selection, or “survival of the fittest,” as the driving force behind evolution. For example, in a lion pride, the strongest cubs are more likely to survive and reproduce, passing on their advantageous traits. Over generations, these accumulated changes can lead to the emergence of a new species.
Jean-Baptiste Lamarck theorized that species evolve by acquiring new traits in response to environmental needs. He believed that disuse could lead to the loss of traits, like snakes losing their legs.
Darwinism and Genetics
Darwin’s theory lacked a mechanism for inheritance. Later, genetics provided this missing piece, leading to neo-Darwinism, which combines Darwinian evolution with genetic inheritance.
The Pace of Evolution
The formation of a new species typically takes about a million years.
Artificial Selection
Humans have influenced evolution through artificial selection, breeding plants and animals for desirable traits.
Evolutionary Radiations
Evolutionary radiations are periods of rapid species diversification and extinction. The breakup of the supercontinent Pangea, for instance, led to increased species diversity.
The Origin of Humankind
Around 8 million years ago, the African continent began to split, forming the Rift Valley. This geological event altered the climate, transforming forests into savannas. Primates, our ancestors, adapted to this change by adopting bipedalism, which offered advantages for foraging. Australopithecus, an early bipedal hominid, emerged around 4 million years ago.
Inheritance and Evolution
Living organisms, unlike inanimate matter, can reproduce. Offspring inherit traits from their parents.
Living things evolve through slight variations in these inherited traits. Natural selection favors the “fittest” individuals, while humans practice artificial selection by choosing desirable traits in plants and animals.
Mendel and Genes
Gregor Mendel’s work revolutionized our understanding of inheritance. He demonstrated that traits are passed down through discrete units, now known as genes, which retain their individuality across generations. Each trait is influenced by two versions of a gene, one from each parent.
In 1909, Wilhelm Johannsen coined the term “gene” for Mendel’s “hereditary factors.” A gene is a unit of hereditary information that controls a specific trait.