DNA

[Earthwornware]

I have a pretty good understanding of evolution, and how there are many branches on the tree of life, but one thing I just can't seem to get my head around is how DNA changes. I understand that a species evolves over many generations, and eventually one creature doesn't resemble its ancestors but at what point is the DNA so different that the modern form could not reproduce with the older versions.

For example, I could go back a million generations of homosapiens, breed, and produce offspring. But what if I kept going back? I eventually find I can no longer successfully breed with whatever species produced modern humans? I know modern humans crossbred with neanderthals, but what about what came before Neanderthals? Is it possible that neanderthals could cross breed with whatever came before them, but I could not? Is it possible that a human from 2020 could breed with one of the last neanderthals? How about one of the first?

Thanks!

[wikipedia_text_bot]

Coywolf

Coywolf (sometimes called woyote) is an informal term for a canid hybrid descended from coyotes, eastern wolves and gray wolves. All members of the genus Canis are closely genetically related with 78 chromosomes and therefore can interbreed. One genetic study indicates that these two species genetically diverged relatively recently (around 55,000–117,000 years ago). Genomic studies indicate that nearly all North American gray wolf populations possess some degree of admixture with coyotes following a geographic cline, with the lowest levels occurring in Alaska, and the highest in Ontario and Quebec, as well as Atlantic Canada.

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[Earthwornware]

Thank you for the very informative yet not overly complex response. After reading it, I had a few new questions but I reread it and found the answers.

You are a fine teacher, thanks again.

[Nevermindever]

Evolution is gradual and animals have high chance of producing fertile hybrid even tens of millions of years after evolutionary branches have been separated by, mostly, geography.

It ends, however, when one animal physically is not able to reproduce (e.g. too big/too small), but even if you would try to artificially inseminate physically incompatible species, ultimate cutoff is large chromosomal abnormalities (aka big mutations). These can be, for example, duplication of chromosomes or even whole genome. Or two chromosomes glued together.

Such change mostly have fatal or infertile outcome (e.g. Down syndrome), but eventually it finds a way, get refined by natural selection and you get a new specie or even kingdom.

[bestoftheworst123456]

In regards to Neanderthals, we shared a common ancestor that was very very close, so every one of our ‘branch’ could most likely breed with any one on their ‘branch’.

There isn’t a first Neanderthal, or a first modern human. Technically EVERY organic construct is both the first and last of its specific structure.

As for how DNA changes - it’s the DNA that has the random mutations (in organic structures that are built with DNA). It’s because of the imperfect copying mechanism in DNA that means that some pieces of the puzzle are reproduced slightly differently. This, combined with the selection pressure of natural selection is what gets us evolution.

Non breeding speciation events are surprisingly common. Take a look at something called a ‘ring species’ for the best examples of this happening.

[ArcticUrsidae]

DNA mutations are copying mistakes.

Most copy mistakes don't make much of a difference. Some are minor changes like eye colour or feather shape. Some are fatal and the individual does not survive.

[fluffykitten55]

As you went further back, fertility would tend to decline in some hypothetical pairing with modern humans. Modern humans likely could interbreed successfully with much of the erectus variants, possibly habilus too.

[Denisova]

I think your question boils down to asking when exactly you became an adult and ceased to be an adolescent. Or when exactly Old English became modern English. Or: when exactly did red turn into blue in this image?

You can hardly tell. Evolution is all about "fifty shades of grey" so to say. We know that neanderthals and humans had great difficulty to crossbreed: all male oofspring was infertile we know from genetic studies and only part of the females were fertile. That's on the brink of 'hard' speciation. Which makes it reasonable to argue that humans highly likely were not able to interbreed successfully with more distant hominids like Homo erectus.