Our bodies are continuing to change shape and size and diet, fitness, environment and medicine all play a part. "Males and females deposit fat in different places in the body – women around the hips and the bust, whereas males more on the stomach. That is part of why breasts have increased in size – because it is a depot for fat. "There is another thing we suggest – in the last 20 to 30, maybe 50 years, there was an introduction to our environment of additional oestrogen-like substances. Therefore, more males now develop a female pattern of fat distribution whereas females exaggerate typically female fat distribution on buttocks and breasts and hips." The increase in oestrogen-like substances is both dietary and environmental, Henneberg explains. "For example soy, which is contained in a lot of products in our diet, contains very well known oestrogen-like substances," he says.

"It is also environmental – some of the plastics used to produced water bottles contain oestrogen-like substances that get into the water circulation and earlier on, the female contraceptive pills were producing higher levels of oestrogen in urine which got into sewers and circulated in water." As well as our busts, our bodies have changed dramatically over time and our changing diet is not the only cause. How our bodies have changed Four million years ago our ancestors were about 1.2 metres tall. Now, the average Australian male is 175.6 centimetres tall and the average female 161.8 centimetres. Interestingly, while we were growing taller, our body weight decreased between 4 million and 10,000 years ago.

"Our trunk reduced in size while our legs became bigger," Henneberg explains. "It is very significant because, compared with our ancestors, we only have 60 per cent of gut size. Our guts, and our whole trunk, became smaller and this is the result of us moving our diets to richer foods – foods of better quality. We had less gut size to digest food because we cooked food and prepared food before we ate it." Then, at the end of the Ice Age up until the 20th century, there was a reduction in body height and body weight. "Ten thousand years ago, we were as tall as we are now, then body height reduced during the Middle Ages to 10 centimetres less and it only came back in the last 100 years," Henneberg says. Why? Agriculture. "We moved from the hunting and gathering which produced a protein rich-diet to a carbohydrate diet with very little protein, plus there were periodic famines which meant shorter and smaller people were advantaged because they needed less food so they could survive better," Henneberg says. "The last 100 years was a return to the body height we lost over the last 10,000 years. With improved living conditions and nutrition, we gained a few centimetres."

How our bodies are changing According to Henneberg humans have now reached our genetic potential for height and it is unlikely we will grow much taller (he adds that biomechanically, growing taller than two metres puts strain on the heart). While our vertical growth spurt may have stopped, our horizontal growth spurt continues exponentially. In 1980, 10 per cent of Australian adults were obese while 60 per cent were within a healthy weight range. Today, more than 60 per cent of us are overweight or obese. "Body weight is expanding because first of all there is the lifestyle – we eat too much and we don't exercise physically enough but that's not the whole story," Henneberg says.

He explains that he and colleagues have been working to show that the growing obesity epidemic is also the result of an increase in gene mutations affecting metabolism. The reason for this increase, Henneberg suggests in new research is that medical intervention has replaced natural selection. "Most of natural selection operates as a janitor and cleans mutations away as they occur to maintain the state of our gene pool," he says. Gene mutation – a chemical process – is not uncommon, Henneberg says, but before modern medicine, our bodies could not fix the problems they caused. "We have, by good medical care, by saving the lives of infants and children and young people, reduced most of natural selection that previously eliminated some of the faulty genes," he says. "One hundred years ago a person with type 1 diabetes could not survive much beyond age 20. Now all those people are very good members of society and families... so now there is less elimination of the faults through natural selection and there is more food so they combine to produce more overweight people." For this reason, Henneberg anticipates that we will continue to expand – our collective waistline and our collective bust sizes.

"The prediction is our bodies will remain about as tall as they are but the fat deposits will change," he says. "The positive news is that with awareness, people are trying to improve their diet. We have to improve what we eat and a bit more physical effort. As usual it is up to us."