A4.1 Evolution & Speciation
Definition of Evolution
Evolution can be defined as the change in the heritable characteristics of a population. A population is a group of the same species. Acquired characteristics are not inherited and do not lead to evolution.
Example
A tennis player who has developed strong muscles in their right arm through training would not pass that muscle strength on to their children.
Since evolution involves changes in heritable traits, it reflects changes in genes. There is a clear pattern: the more closely related two species are—based on morphology and other characteristics—the fewer differences they have in the base sequences of their genetic material.
Selective breeding as evolution evidence
Humans have selectively bred animals for thousands of years to enhance desirable traits, a process known as artificial selection. This has led to significant changes in species over relatively short periods of time. The fact that humans have driven noticeable evolutionary changes in just 12,000 years supports the idea that natural evolution, acting over billions of years, can similarly shape organisms—even without human involvement.
Homologous vs Analogous Structures
Homologues structure: Same structure, different function. Provides evidence of divergent evolution.
Example: Pentadactyl limbs
Analogous structure: Same function, different structure. Provides evidence of convergent evolution
Example: Human vs Octopus eye.
Example
Homologous Structures: Pentadactyl Limbs
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Analogous Structures: Human vs Octopus Eyes
Speciation by Isolation [Super Important]
Speciation is the process in which a new species emerges from a pre-existing one. It’s a process that occurs on the duration of generations, and its effects can only be seen when a long time passes. It occurs when a species is reproductively isolated (Geographical, Behavioral or temporal isolations.) These reproductively isolated species will no longer have mixed gene pools (gene pool will diverge) , which will result in a change in allele frequence due to being exposed to different selection pressure (forces species to mutate). When a long enough time passes, these species will have developed so many different traits, and if they were to interbreed, they would produce and sterile offspring. Since their offspring is not fertile, then they are not the same species, meaning that speciation has occurred.
The most common type of reproductive isolation is; Geographical isolation due to abiotic barriers. This type of speciation is called allopatric.
There is also another speciation type called sympatric; this is due to behavioral/temporal isolations, so the organisms don’t have to be separated geographically.
Behavioral: The organisms mating habits do not match
Temporal: The organisms mating time/seasons do not match
Differential Selection
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Directional Selection (One Extreme phenotypes are favored for survival)
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Stabilizing Selection (The Average phenotype is favored for survival)
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Disruptive selection ( The extremes phenotypes are favored for survival)
Refers to when different environmental pressures lead to distinct adaptations in isolated populations.
There is three type of differential selections:
Adaptive Radiation
Adaptive radiation is when one species quickly evolves into many new species, each adapted to a different environmental niche.
Higher Level
Example
A single species of finch arrived on the islands. Over time, they evolved into many different species with different beak shapes, depending on what food was available — like seeds, insects, or cactus.
Hybridization
If organisms cross breed (Interspecific hybridization), they will produce hybrids that are sterile, these hybrids have useful traits, but in evolutionary terms, the resources (Sperm and egg) expended on sterile organisms are considered wasted. This occurs when there is genetic incompatibility, such as the offspring inheriting an odd number of chromosomes, which causes abnormal meiosis.
Higher Level
Hybridization
Polyploidy's the inheritance of more than two sets of homologous chromosome; it occurs as an error in cell division. This error can lead to an abrupt speciation (sudden). Polyploid embryos are typically non-viable for humans, but they are quite common in plants, making them more ripen and delicious. Polyploid organisms cannot reproduce to diploid, this raises an interesting question: are polyploid individuals perhaps new species?
