Week8 The Darwin's Finches

Hello, everyone.
In this week, I will introduce about the Darwin’s Finches which have different beak according to their food.






14 kinds of Darwin's Finches inhabit the Galapagos Islands which contain more than 10 islands and locate about 900km west from mainland of Ecuador. After Charles Robert Darwin treated Darwin's Finches as an object of the theory of evolution, it was investigated in detail for 20 years from 1973. They conducted follow-up survey about the kind, the figure and the food o more than 1000 Darwin's Finches which live one island continuously. Then, they discovered that the height of the beak changes little by little with individuals also in the same kind of the same group. For example, on the Daphne Island, the range of the height of a beak of Medium Ground Finch which is a kind of Darwin's Finches is 7 to 11 mm and the average is 9 mm generally.




The difference in the height of the beak between these individuals can be divided into an environment difference and the difference arising from heredity. I will talk about the difference arising from heredity. The difference in the beak between Finch's individuals is closely related to what kind of food the individual eats. As a result of researchers investigating, it is suitable for breaking hard food as an individual with a high beak. However, it is not suitable for eating a small seed as an individual with a large and high beak. The drought happened in the Galapagos Islands in 1977. Therefore, large and hard fruits, for example tribulus and cactus, and increased, and small and soft seeds have decreased. As a result of it, the individuals with a high beak survived more than the individual with low beak. And the surviving individual with high height of a beak bred. Then the children which were born after the drought also have high beak. Their beak become 1 mm higher on the average. The difference in the height of a beak made the difference of the probability of survival and, as a result, the natural selection that an individual with a high beak spread happened. (The natural selection was introduced in last week.) Several years later, the climate of Galapagos Islands has changed into heavy rain and high temperature by El Nino. Therefore, small and soft seeds have increased, and large and hard fruits have decreased. Then, a small individual with the beak with which the point sharpened came to increase because they were advantageous to eating a small seed. The natural selection was happened again.

The difference in the size of beak or body by Darwin’s Finches’ food is also happen by distribution of the animals and plants of each Island. Among Darwin’s Finches, there are a kind which eats seeds, a kind which eats the skin of iguana, a kind which eats insects and, surprisingly, a kind which suck blood of other birds. Darwin's finches can teach the mystery of natural selection.




That’s all in this week.
Next week, I will talk about the problems the Galapagos Islands have.
Thank you for your reading. See you then.