With this in mind, be wary of one trick creationists play when hearing this. They'll say they admit that there are genetic changes within species, but God created all unique species in their 'kind' and no single species ever evolved into another distinct species. Here is an example of the kind of thing they say, from the execrable Answers In Genesis site:
"As creationists, we must frequently remind detractors that we do not deny that species vary, change, and even appear over time. The biodiversity represented in the 8.7 million or so species in the world is a testament, not to random chance processes, but to the genetic variability and potential for diversification within the created kinds."
Let's not focus on the long-standing misunderstanding about evolution being "random chance processes" (it is not), as I've covered that in other blog posts, but instead focus on the attempt to mislead by denying that creatures can evolve into different species. The first thing to point out here is that just as God gave Adam the dignity of naming the animals - which is not a literal story, of course, but a story that conveys the sovereignty and responsibility God has given humans over the planet. It is also humans who get to name creatures according to markers, and it is those markers that we've called 'species', based on our empirical observations in biological evolution.
We have classified two organisms as being different species if they will not or cannot produce fertile offspring together. That is how we've defined species - it has nothing to do with how different things look. Two organisms can look very similar and be a different species, and they can look quite different and still be the same species. Speciation is usually the consequence of gradual change in isolation from the species from which it departed. So as the progeny of each generation accumulates more and more slight genetic differences, at some point there is enough distinction so that some of them will not or cannot produce fertile offspring. At that point, it is not hard to understand that the future generations of these two different species will be growing farther and farther apart in whatever changes happen in them because they will not interbreed.
At this point you have two separate branches on the family tree that constitute two different species. Some species adapt to live so closely together that they cannot survive without one another. We, for example, cannot live without bacteria in our guts. There are also conditions under which two species have merged, and the genome of one has been almost completely transferred into the other, such as when bacterial consortia are found. A consortium is a group of different bacteria where the waste product of one, be it ammonia or oxygen or hydrogen sulphite, etc, is the food of another. The material coming into the consortium is recycled, often leaving a very efficient colony. The transfer of materials between consortia members is limited by the surface area that they can share. If only one member could get inside another then the whole process would be even more efficient. This has happened at least twice in the history of life (although probably much more often), including in our lineage. Once one species is inside the other, a strange situation occurs. Both have separate genomes that compete with one another, yet they still rely on one another. It is like a battle between co-dependent friends.
As natural selection tends towards survivability on a fitness landscape, and as interbreeding has now ceased, new species will gradually become more and more genetically different over time from the creatures with which they were once more closely related. It is perhaps difficult to imagine how those gradual changes could produce so many diverse creatures in the animal kingdom, and why it can be hard for creationists to believe humans are genetically related to chimpanzees, elephants, cats and fish. But if you think of the rich diversity of domesticated dogs in just a few thousand years of artificial selection in dog breeding, and a few tens of thousand of years since their descent from grey wolves, then it should be possible to contemplate how much diversity of change can occur with the animal kingdom over millions and billions of years.
This is a passage from Francis Collins’ brilliant book The Language of God, in which he sums up the sheer magnitude of time that we are considering:
“If the 4.6 billion years of the earth’s existence from initial formation to today were compressed into a twenty-four hour day with the earth being formed at 12:01am - life would appear at about 3:30am. After a long day of slow progression to multicellular organisms, the Cambrian explosion would finally occur at about 9pm. Later that evening dinosaurs would roam the earth. Their extinction would occur at 11:40pm, at which point the mammals would begin to expand. The divergence of branches leading to chimps and humans would occur with only one minute and seventeen seconds remaining in the day, and anatomically modern humans would appear with just three seconds left. It is not surprising that many of us have a great deal of difficulty contemplating evolutionary time.”
The human genome project has provided for us accurate information about the whole history of evolution through analysis of DNA and the chain of events which led to ourselves and other primates. Scientists are even very sure that they know at which point in the tree of evolution the chromosomal fusion occurred in our ancestors for Homo-sapiens to evolve.
I am certain that most of the Christian objections to the long history of evolution on our planet are psychological objections; after all, we are so used to seeing that if the devotional aspect of our inner-self has planted a tree of Divine hope in our hearts, the harsh realities of a long protracted ‘tooth and claw’ evolutionary process tend to wave a threatening axe in front of the tree. But it is not so.
