Speciation Natural selection genetic drift and barriers to

Speciation Natural selection, genetic drift and barriers to gene flow can all lead to changes in the relative frequencies of alleles in a population, which can lead to speciation. Speciation is the formation of new species. A species is a group of organisms that breed with one another and produce fertile offspring.

Speciation The gene pools of two populations must become separated in order for them to become two separate species. As new species evolve, populations become reproductively isolated from each other. When the members of two populations cannot interbreed and produce fertile offspring, reproductive isolation has occurred.

Speciation Reproductive isolation can develop in a variety of ways, including: Behavioral Isolation Habitat Isolation Geographic Isolation Temporal Isolation Gametic Isolation Mechanical Isolation Reduced Hybrid Viability Hybrid Sterility

Speciation Behavioral Isolation occurs when two species attract mates by using different mating signals or courtship rituals.

Speciation Habitat Isolation occurs when two species live in the same geographical area, but do not meet because they live in different specific habitats in that area.

Speciation Geographic Isolation occurs when two species live in the different geographic areas, and never meet in the wild.

Speciation Temporal Isolation occurs when two species breed at different times. They could be separated by as little as a few hours, by seasons, or even by years.

Speciation Gametic Isolation occurs when two species cannot breed because their gametes (eggs and sperm) cannot interact, even when they come into contact with each other.

Speciation Mechanical Isolation occurs when two species cannot breed because they are anatomically (structurally) incompatible.

Speciation Reduced Hybrid Viability occurs when two species can breed, but the hybrid offspring produced do not live to reproductive age.

Speciation Hybrid Sterility occurs when two species can breed and the hybrid offspring survive, but these hybrids are sterile.

Evidence for Evolution Day 3

Hominid Evolution

Benchmarks SC. 912. L. 15. 10 Identify basic trends in hominid evolution from early ancestors six million years ago to modern humans, including brain size, jaw size, language, and manufacture of tools.

Objectives Identify early human ancestors in terms of their scientific names, place of origin, and evolutionary trends.

Essential Questions How do the defining characteristics of hominids differ among the variety of species within the group. How did characteristics such as brain size, jaw size, language, and the use of tools change over the 6 million year time period that hominids have existed? How have the changes that occurred in hominids’ brain size, jaw size, language, and tools over time lead to a more successful organism?

Hominid Evolution Between 6 and 7 million years ago, the hominoid line, or the great apes, gave rise to hominids. The hominid family includes modern humans. As hominids evolved, they began to walk upright and developed thumbs adapted for grasping. They also developed large brains.

Hominid Evolution

Hominid Evolution The skull, neck, spinal column, hipbones, and leg bones of early hominid species changed shape in ways that enabled later hominid species to walk upright. Evolution of this bipedal, or two-foot, locomotion freed both hands to use tools. Hominids evolved an opposable thumb that enabled grasping objects and using tools. Hominids displayed a remarkable increase in brain size, especially in an expanded cerebrum—the “thinking” area of the brain.

Hominid Evolution There as many as 20 separate hominid species. This diverse group of hominid fossils covers roughly 6 million years. All are relatives of modern humans, but not all are human ancestors. Questions remain about how fossil hominids are related to one another and to humans.

Hominid Evolution Researchers once thought that human evolution took place in steps, in which hominid species became gradually more humanlike. Today researchers believe Hominid evolution did not proceed by the simple, straight-line transformation of one species into another. Rather, a series of complex adaptive radiations produced a large number of species whose relationships are difficult to determine. Adaptive radiation is a process by which a several species evolve a single ancestral species.

Hominid Evolution The hominid fossil record dates back 7 million years, close to the time that DNA studies suggest for the split between hominids and the ancestors of modern chimpanzees. Millions of years ago

Hominid Evolution Other species in the genus Homo existed before Homo sapiens. The first fossils in the genus Homo are about 2. 5 million years old. These fossils were found with tools, so researchers called the species Homo habilis, which means “handy man. ”

Hominid Evolution 2 million years ago, a species called Homo ergaster appeared. It had a bigger brain and downward-facing nostrils that resembled those of modern humans. At some point, either H. ergaster or a related species named Homo erectus began migrating out of Africa through the Middle East.

Hominid Evolution The story of modern humans over the past 500, 000 years involves two main groups. The earliest of these species is called Homo neanderthalensis. Neanderthals lived in Europe and Asia 200, 000– 30, 000 years ago. They made stone tools and lived in organized social groups. The other group is Homo sapiens—people whose skeletons look like those of modern humans.

Hominid Evolution 50, 000– 40, 000 years ago some populations of H. sapiens seem to have changed their way of life: They made more sophisticated stone blades and elaborately worked tools from bones and antlers. They produced cave paintings. They buried their dead with elaborate rituals. About 40, 000 years ago, a group known as Cro-Magnons appeared in Europe. By 30, 000 years ago, shortly after the appearance of Cro. Magnons, Neanderthals had disappeared from Europe and the Middle East. For about 10, 000 years, our species has been Earth’s only hominid.

Hominid Evolution About 40, 000 years ago, a group known as Cro-Magnons appeared in Europe. By 30, 000 years ago, shortly after the appearance of Cro. Magnons, Neanderthals had disappeared from Europe and the Middle East. Cro-Magnons, the earliest members of our species, differed only slightly from modern humans. For about 10, 000 years, our species has been Earth’s only hominid.