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The theory of evolution by natural selection explains how species change over time. The core mechanism: within any population, individuals vary in traits. Some traits improve survival and reproduction in the current environment. Those individuals pass more genes to the next generation. Over many generations, the population shifts.
This isn't random chance. Natural selection is a sorting mechanism — it consistently favours traits that improve fitness in a given environment. But which traits help depends entirely on the environment. In a changing environment, evolution can happen surprisingly fast.
Evolution is supported by multiple independent lines of evidence: the fossil record showing gradual changes over time, genetic analysis showing shared ancestry, direct observation of evolution happening (bacteria developing antibiotic resistance, for example), and comparative anatomy showing homologous structures across species.
Humans share about 99% of our DNA with chimpanzees, about 85% with mice, and even about 60% with banana plants — we're not descended from chimps but share a common ancestor from about 6-7 million years ago.
by triciaprescod64597
The human brain contains roughly 86 billion neurons connected by about 100 trillion synapses — connections between neurons. Information travels as electrical impulses along neurons and chemical signals across synapses.
Different regions specialise in different functions. The prefrontal cortex handles planning, decision-making, and personality. The hippocampus forms and retrieves memories. The amygdala processes emotions, particularly fear. The cerebellum coordinates movement and balance. The brainstem controls basic survival functions like breathing and heart rate.
Memory isn't stored in one location but distributed across networks. Long-term memories form through synaptic strengthening — when neurons repeatedly fire together, their connections strengthen, which is why practice and repetition improve memory. Sleep is critical for consolidating memories from short-term to long-term storage.
The brain is remarkably plastic, especially in youth. It reorganises in response to experience and learning. Neuroplasticity continues in adulthood, though more slowly. This is why learning new skills at any age remains beneficial and why stroke rehabilitation can be effective.
by asanteowusu38006
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