Here is an enlightening video series that explains evolution in simple terms. Part 5 is particularly interesting:
If you find that interesting, start the series with part 1: Facts Of Evolution – (Chapter 1 of 6)
A quote from Chapter 1:
Every living thing on earth is related to every other living thing on earth. A common misconception is that some modern species are descended from other modern species. This is rarely the case. Instead, closely related modern species descended from a common ancestor, that is neither one or the other. Humans did not come from chimps. Both humans and chimps came from a creature that had more primitive deatures than either modern humans or modern chimps.
If it is to be called Science, it must be testable. And for almost 150 years, the research community has done every test imaginable to examine evolution and common descent. And for 150 years, not a single test has ever failed to validate that all life on earth comes from one common ancestor.
In other words, evolution is a proven fact. The evidence is undeniable.
Where did life start? Why would life start? Why does life continue? How can life become more complex over time? Here is one way to think about it:
In their study, which is published in the International Journal of Astrobiology, the researchers considered a primordial pool that contained some basic compounds. By reacting with one another and coupling with an external energy source such as the Sun, the compounds formed a chemical system. The compounds continually engaged in chemical reactions, thriving the most when capturing and distributing more and more of the Sunâ€™s energy in the quest for a steady state. The evolutionary process was and still is non-deterministic, even chaotic, since the energy flows create energy differences that in turn affect the flows.
Due to random variations stemming from the chemical reactions, some novel compounds may have emerged in the primordial system. Some of these compounds (such as those involving carbon) might have been exceptionally good at creating energy flow, enabling the system to diminish energy differences very efficiently and reach a higher level of entropy.
The scientists give several examples of mechanisms associated with life that increase entropy. For instance, when systems (e.g. molecules) become entities of larger systems (e.g. cells) that participate in larger ranges of interactions to consume more free energy, entropy increases. Genetic code might have served as another primordial mechanism, acting as a catalyst that could increase energy flow toward greater entropy. Today, complex organisms have cellular metabolism, which is another mechanism that increases entropy, as it disperses energy throughout the organism and into the environment. The food chain in an ecosystem is another example of a mechanism for transferring energy on a larger scale.
In this sense, life is a very natural thing, which emerged simply to satisfy basic physical laws. Our â€œpurpose,â€ so to speak, is to redistribute energy on the Earth, which is in between a huge potential energy difference caused by the hot Sun and cold space. Organisms evolve via natural selection, but at the most basic level, natural selection is driven by the same thermodynamic principle: increasing entropy and decreasing energy differences. The natural processes from which life emerged, then, are the same processes that keep life going â€“ and they operate on all timescales.