Yes. The common ancestor of all animals lived more than 500 million years ago. So by comparing the genome sequences of lots of different animals (from different phyla) we can infer what the genome of the common ancestor would have been like. For example, which genes would or would not have been present in that common ancestor.
Yes, I think the common ancestor has explained that really well.
What sequencing more genomes gives us is an ability to look for similarities and differences between groups. So, for example, if you were to sequences us you could compare out genome with a shallow water fish such as Cod to see where we are similar and what differences allow us to live in the deep. Similarly you could compare genomes of a variety of deep sea fish to see if there are genes all of us use in a special way that lets us all live in the deep sea. You can also then compare back to further ancestors, just like the common starfish said, and see what genes we have in common with species 500 million years ago and see what we have changed!
Hi topquestionsfromchat. Interesting name. 🙂 You’ve already got 2 great answers to your question, and they are absolutely right. Comparing the genomes of different organisms allows you to study how similar or different they are and also, by taking rates of mutation into account, it can give you a sort of timeline for when changes took place.