BBC4 recently screened a fascinating programme on the human body: Can Science Make Me Perfect?. Alice Roberts, Professor of Public Engagement in Science at the University of Birmingham and an excellent presenter (her Wiki page calls her "an English anatomist, osteoarchaeologist, physical anthropologist, palaeopathologist, television presenter and author.") was given the challenge of redesigning the human body to avoid its weaknesses and add some strengths. So she identified some major weaknesses and looked for solutions elsewhere in the animal world, plus considered what else might usefully be adopted.
Some of the proposed improvements were very subtle and would not be noticeable to the naked eye: for instance, we get heart attacks because we only have one major artery for each side of the heart, and these can get blocked. Some animals (including dogs) have a network of interconnecting blood vessels in and around the heart, so if one gets blocked, there are always alternative routes. Also, some animals have small "secondary hearts" to help with circulation - one of those in each thigh would greatly help with common circulation problems causing varicose veins etc. Another subtle one is a redesign of the throat area to provide a better separation between swallowing and breathing, to minimise the risk of choking (and snoring!). Also, our lungs are very inefficient compared with birds, who have a much better air-handling system, so that can be added to the list.
Other suggested changes are more obvious - and controversial: back problems bother many of us, so a redesign of the lower back to strengthen and support that area would help. Pregnancy and childbirth are highly problematic for humans because of our huge head - but marsupials get over this by giving birth to jelly-bean sized babies which grow to full size in an external pouch, so add that in. Most striking of all are the legs: ours were originally developed for tree-climbing and moving about on all fours and are badly designed for walking and running, causing us all sorts of problems in our complicated joints and tendons. Bird legs like those of an ostrich or emu are more specialised and allow the birds to maintain a high running speed for long periods with minimal stress and energy expenditure.
Finally some minor improvements: larger, steerable ears to enable us to focus our attention on what we want to hear even against a noisy background, and more efficiently designed eyes so we can see more clearly - including in the dark. One very useful change – the addition of melanin chromatophores to our skin, so that it quickly becomes dark brown in strong sunlight to protect us from burning and skin cancer, but lightens up in other circumstances to allow the formation of vitamin D (not mentioned was that this might well help to solve some persistent social problems).
As these ideas were developed, an anatomical artist was working on the design, with model-makers from the film world making a full-sized model of what she would look like with all of these changes. There is a a photo of the result (standing next to the original) here: https://static1.squarespace.com/static/58cebafa197aea5216423456/t/5b1eac7d1ae6cf3e98b23b35/1528736940398/MF5B9921.jpg taken from her website: https://www.alice-roberts.co.uk
A thought-provoking programme, which was instructive in explaining how the human body has evolved rather imperfectly. On the other hand, there would also be downsides to some of the changes proposed (e.g. babies develop more slowly out of the womb, so a marsupial mum's pouch would be occupied for years).
I would add a couple of suggestions to her list: the ability that some dogs apparently have to identify illnesses in people, including cancers, just by smell. Now that would really be useful – think of the savings in screening programmes! Even more so would be to acquire the ability of the naked mole rat to be highly resistant to cancers.