Question

SHARK HUMAN Adult shark 29 days 49 days 56 das Extemal carotid Ductus arterosus Aorta Figure 2.18 shows the arrangement of branching blood vessels in adult sharks and humarn embryos at various stages of development At which of the stage of human development pictured does the pattern of blood vessels look most similar to the pattern found in sharks? 1. If scientists were only to examine human embryos at 56 days, would the homologies be apparent? 2. 3. Why are these homologies only present in the earlier embryos? 4. Why does this homology indicate fishes and humans share a common ancestor?

Answer 1

ANS 1) In the holoblastic pattern of cleavage where the entire egg is divided into smaller cells, as it is in frogs and mammals

ANS 2) In the human being only the first 56 days of development are covered and embryo is usually called fetus. So, the homologies is not apparent or learly visible it will be visible only after 4-5 weeks of pregnancy.

ANS 3) Homologies present in earlier embryo are the ones similarities which are seen previous to adulthood. They too serve as proof that the species in query is related to some other species, even supposing those similar organs or anatomical structures are simplest located in embryos

ANS 4) Embryonic homology indicate that fishes and humans share a common ancestor because 1)like fish, human embryos have gill arches bony loops in the embryo’s neck, 2)In human embryos, the gonads form deep in the chest just like in fish.

In homology, the homologous systems did in fact evolve from a current not unusual ancestor. organisms with homologous systems are extra closely related to every different at the tree of lifestyles than those with analogous structures.But, they're still carefully related to a latest commonplace ancestor and have most likely passed through divergent evolution wherein closely related species come to be much less similar in shape and characteristic because of the adaptations they accumulate for the duration of the natural choice manner,migration to new climates, competition for niches with other species, and even microevolutionary adjustments like dna mutations can make a contribution to divergent evolution.