Extinction is often caused by a change in environmental conditions. When conditions change, some species possess adaptations that allow them to survive and reproduce, while others do not. If the environment changes slowly enough, species will sometimes evolve the necessary adaptations, over many generations. If conditions change more quickly than a species can evolve, however, and if members of that species lack the traits they need to survive in the new environment, the likely result will be extinction.
2. Does evolution proceed toward increasing complexity?
In the approximately 3.8 billion years since life originated on Earth, evolution has resulted in many complex organisms and structures. The human brain and stereoscopic eyes are just two examples. At the same time, simpler organisms like algae, bacteria, yeast, and fungi, which arose several billion years ago, not only persist but thrive. The presence of single-celled organisms alongside complex organisms like humans testifies to the fact that evolution within a given lineage does not necessarily advance toward increasing complexity. When more complex organs are advantageous, complex organs have arisen. Single-celled organisms, however, fill many roles, or niches, much better than any multicellular organism could, and so they remain in a relatively stable state of adaptation.
3. If fish became amphibians through the process of evolution, then why do fish still exist?
Fossil evidence clearly shows that amphibians descended from one group of ancient fishes whose thick, bony fins gradually evolved into limb-like appendages. Other species gave rise to the kinds of fish that inhabit oceans, lakes, and streams around the world today. Fish, like all living creatures, continue to evolve. This evolution is not toward a life on land, but instead toward successful use of the underwater environment. There are countless ecological opportunities under water, which is why fish still exist. When the earliest ancestors of modern amphibians left the water, they found many new opportunities on land. As amphibians and other land creatures diversified, however, fewer and fewer opportunities existed for newcomers.
4. Could apes ever evolve into some other humanlike creature?
It is possible that in many millions of years present day apes could evolve into some other humanlike species. It is, however, very improbable. First of all, humans did not evolve from any of the species we know as apes today. At some point 5 to 8 million years ago, the common ancestor of humans and modern apes diverged to form the two separate lineages we know today. The species at the end of these lineages are a result of a very specific combination of selection pressures and genetic mutations over millions of years. This same combination is highly unlikely to occur ever again.
5. Are humans influencing the process of evolution?
Most scientists would agree unequivocally that humans have greatly affected the process of evolution, from the rise of antibiotic and pesticide resistance to the largely human-caused increase in the extinction rate. Our effect on the process of evolution even extends to our own species’ evolution. Technology and culture have protected us to a great extent from the selective pressures that drive evolution, allowing many people — especially those in developed nations who, without medical intervention, would not live to reproductive age — to pass their genes on to the next generation. Other scientists note that technology and culture have changed but not eliminated the role of natural selection on our species. We now adapt to crowding, pollution, and new disease rather than the necessity to escape from large predators. Humans will change in the future, but are unlikely to evolve into a new, separate species because no human group is truly isolated anymore, given our transportation systems. Without genetic isolation, there is no further opportunity for speciation among humans.
6. If humans evolved from apes then why are there still apes?
Humans did not evolve from present-day apes. Rather, humans and apes share a common ancestor that gave rise to both. This common ancestor, although not identical to modern apes, was almost certainly more apelike than humanlike in appearance and behavior. At some point — scientists estimate that between 5 and 8 million years ago — this species diverged into two distinct lineages, one of which were the hominids, or humanlike species, and the other ultimately evolved into the African great ape species living today.