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By Root 293 0

female, known formally as the “mitochondrial coalescent” but dubbed “mitochondrial Eve,” gave rise to every living human today. Between 80,000 and 60,000 years ago, a large population from the center of Africa migrated to all areas of Africa, as well as the area of present-day Saudi Arabia. This migration may have taken two routes, a northern one up the Nile and around the Red Sea and a southern one across the narrow strait at Yemen which during the last ice age would have been only five kilometers across (Forster thinks the southern route was the more likely). Between 60,000 and 30,000 years ago there was a great migration to Southeast Asia, Northern Asia, and Europe. Between 30,000 and 20,000 years ago, people spread throughout most of the rest of the world, including Australia, and between 20,000 and 15,000 years ago they migrated into North America, making their way into South America between 15,000 and 2,000 years ago. The final migration over the past 2,000 years saw the settlement of the Pacific islands.

Creationists who take comfort in the “Eve” part of this account should know that other scientists believe that we arose from a single population, not one individual, and still other scientists opt for the multiregional theory of human origins, in which different human groups arose from different ancestral groups who migrated out of Africa at different times. And in any case, this is just the story of our most recent ancestors; our lineage goes back at least as far as six million years ago to the common ancestor of apes and humans.

What Direct Evidence Is There

for Natural Selection and Evolution?

Every year for the past three decades the husband and wife team of Peter and Rosemary Grant, both from Princeton University, have parked themselves on the Galápagos island of Daphne Major, a tiny volcanic plug 120 meters high and a kilometer long, to study the evolution of Darwin’s finches.

We now have extensive evidence from both fossils and genes that three million years ago a single group of finches flew out to the Galápagos during a time of very active plate tectonics and the creation of the island archipelago. When this founder population arrived, it encountered a permanent El Niño that made the islands warm and wet, which helped to trigger an explosion of speciation.

First came the warbler finch, then the tree finch (of which there are now five species), and then the ground finch (of which there are now six species). Following Ernst Mayr’s theory of allopatric speciation (in which a founder daughter population breaks away from the parental population), the first finches landed on San Cristóbal, then migrated to Española, then to Floreana, then to Santa Cruz, and finally made their way back to San Cristóbal. Along the journey the finches adapted to local conditions. Finches in highlands developed larger beaks to break hard beetles and seeds. Finches in lowlands evolved smaller beaks for eating small seeds and succulents. As an opportunistic species, some of these finches also ate sea turtle eggs and sucked the blood from blue-footed boobies. Different adaptations to different islands led to the origin of new species.

The Grants provide one of the strongest examples of observing evolution as it unfolds, which they did in tracking thirty years of environmental changes on Daphne Major and how the finch species responded. Arriving in 1973, the Grants immediately witnessed a drought that wiped out 85 percent of the population of two species of finches (the ground finch Geospiza fortis and the cactus finch Geospiza scandens). From 1975 to 1978 there was almost no rainfall and natural selection operated rapidly to change beak size. In 1983, an El Niño rainfall produced an abundance of plants and trees and cactus fruit, but two years later the island dried out and the large seeds were replaced by small seeds. Throughout this cycle, beak shape, beak size, and body size of the finches all changed in parallel.

What Is the Difference between

Natural Selection and Sexual Selection?

On the heels of Margulis’s pronouncement