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A look at the historical context of Charles Darwin's voyage and his findings in the Galapagos.
Imagine visiting five neighboring islands and finding that the same type of bird has a completely different beak on every single one. Why would nature 'design' them that way, and what does it reveal about our own history?
In 1831, Charles Darwin set sail on the HMS Beagle for a five-year journey. His most famous stop was the Galapagos Islands. Darwin noticed that although the islands were close together, they had different environments. He observed that finches had beak shapes specifically suited to their food source: blunt beaks for cracking seeds and sharp beaks for eating insects. Similarly, giant tortoises had shells that differed by island. On islands with low vegetation, tortoises had 'domed' shells. On islands with tall cacti, they had 'saddle-back' shells, allowing their necks to reach higher. These adaptations suggested that species were not fixed, but changed over time to fit their surroundings.
Quick Check
What was the primary difference Darwin noticed among the finches on different islands?
Answer
The shape and size of their beaks, which corresponded to the specific food sources available on each island.
Darwin didn't develop his theory in a vacuum. He was heavily influenced by two thinkers. First, Charles Lyell, a geologist, argued that the Earth was millions of years old and changed slowly through natural processes. This gave Darwin the 'deep time' needed for evolution to occur. Second, Thomas Malthus, an economist, observed that human populations grow faster than food supplies, leading to a 'struggle for existence.' Darwin realized this applied to all nature: if more individuals are born than can survive, only those with the best traits win the competition for resources.
Consider a single pair of elephants. If every offspring survived and reproduced, in 750 years there would be (19 million) elephants. 1. Identify the starting population: 2 elephants. 2. Observe the potential growth: Exponential increase. 3. Identify the reality: Resources (food/water) are limited. 4. Conclusion: Most offspring do not survive, leading to a 'struggle for existence.'
Quick Check
How did Lyell's geological theories help Darwin's biological theory?
Answer
Lyell provided the evidence that Earth is very old, which meant there was enough time for species to change gradually over many generations.
In 1859, Darwin published *On the Origin of Species*. He proposed the mechanism of Natural Selection. He argued that individuals with favorable variations are more likely to survive and reproduce. They pass these traits to their offspring. Over many generations, these small changes accumulate, leading to the emergence of new species. Darwin called this 'descent with modification.' He avoided the word 'evolution' in early editions, preferring to describe how nature 'selects' the best-adapted individuals, much like a farmer selects the best cows for breeding.
Imagine a population of beetles where some are green and some are brown. 1. Variation: A mutation makes some beetles brown () while others remain green (). 2. Selection Pressure: Birds eat the green beetles because they are easier to see on brown bark. 3. Differential Reproduction: Brown beetles survive more often and have more 'brown' babies. 4. Evolution: Over time, the frequency of the brown trait increases in the population until most beetles are brown.
Which observation in the Galapagos most surprised Darwin?
If a population grows at a rate of but food only grows at , what is the result according to Malthus?
Darwin published 'On the Origin of Species' immediately after returning from his voyage in 1836.
Review Tomorrow
In 24 hours, try to explain to a friend how a bird's beak is like a specialized tool and which two scientists helped Darwin realize that nature is a competition over a very long time.
Practice Activity
Look at three different dogs in your neighborhood. Identify one 'variation' (like ear shape or coat thickness) and brainstorm what kind of environment that trait would be an 'adaptation' for.